Ahmed Z. Obeidat, MD, PhD

Sir Augustus d’Este (1794-1848) described the circumstances preceding his development of neurological symptoms as follows:¹ “I travelled from Ramsgate to the Highlands of Scotland for the purpose of passing some days with a Relation for whom I had the affection of a Son. On my arrival I found him dead. Shortly after the funeral I was obliged to have my letters read to me, and their answers written for me, as my eyes were so attacked that when fixed upon minute objects indistinctness of vision was the consequence: Soon after I went to Ireland, and without any thing having been done to my eyes, they completely recovered their strength and distinctness of vision…" He then described a clinical course of relapsing-remitting neurologic symptoms merging into a progressive stage of unrelenting illness, most fitting with what we know today as multiple sclerosis (MS).¹ Why did Sir Augustus d'Este connect the event of the unexpected death to the onset of a lifelong neurologic disease?

Jean-Martin Charcot first described MS in a way close to what we know it as today. Charcot considered stress a factor in MS. He linked grief, vexation, and adverse changes in social circumstances to the onset of MS at that time.² I, as a practicing MS specialist, am surprised neither by Sir Augustus d'Este's diary nor by Charcot's earlier assessments of MS triggers.³ As I write this narrative, I think of the many times I heard from people diagnosed with MS. "It happened to me because of stress" is a statement not estranged from my daily clinical practice

MS as a multifactorial disease

It is tempting to make a case for emotional stress as a cause of MS, but one must remember that MS is a very complex disease with unclear etiologies. MS, a treatable but not yet curable disease, is the interplay between the genetics of the host and numerous environmental factors that exploit a susceptible immune system leading to unrelenting immune dysregulation.⁴ Recent studies have brought some pieces of this intricate puzzle together. The role of Epstein-Barr virus (EBV) in the pathogenesis of MS is being dissected.⁵ The possible synergy between vitamin D deficiency, EBV, and certain genetic variations is being studied.⁶ The roles of smoking, environmental toxins, obesity, diet, Western lifestyle, and the gut microbiome are some of the top areas of clinical, translational, and basic research.^7-11 But what about emotional stress? Where does it fit, if anywhere, in the current research paradigm?

Emotional stress and MS—Causality or not?

In the scientific method, several criteria must be proven for an element to be suspected in the etiology of a disease.¹² First, the suspect element must be present before the disease starts—i.e., a temporal association. Second, there must be a plausible biological explanation of how the suspect element acts in the disease's causation. Third, other variables that could confound the picture must be controlled for or dismissed. It is clear that no single factor is the cause of MS. By now, MS is agreed upon as a disease caused by multiple factors, some of which remain to be unraveled.⁹ The term "cause" has been utilized more recently by many authors when referring to EBV in relation to MS development, reasoning that in one study, in a small number of individuals with MS, EBV infection preceded the MS clinical diagnosis.¹³ Thus, the temporal association was provided. But does MS start at the onset of clinical symptoms?

For Sir Augustus d'Este, the disease may have started years before he visited the Highlands of Scotland, but only at that visit did MS become clinically apparent. So, the emotional trauma may have acted as a "trigger" for an MS flare-up rather than being a "cause" of MS. This might be a more plausible explanation of the association between emotional trauma and MS development. However, MS pathogenesis is complex, and one could argue that the disease starts many years before the first clinical symptoms that lead to diagnosis.

The MS prodrome has been demonstrated by several studies that suggest that MS may start many years before the clinical diagnosis.¹⁴ Radiologically isolated syndrome (RIS) further argues that MS may be clinically dormant for years, and clinical symptoms may not appear until later in the disease process.¹⁵ One may think that immune attacks on the optic nerves, spinal cord, or areas of the brainstem might be readily symptomatic compared to attacks on other structures of the central nervous system (e.g., periventricular or juxtacortical brain areas) that may be clinically silent. So, while for Sir Augustus d'Este it seemed that the disease started at the time of his visit to the Highlands of Scotland, it is equally plausible that it started years before the first clinical attack. Nevertheless, how could emotional stress play a role in the pathophysiology of MS?

Stress and the Immune System

At times of chronic stress, one may become more susceptible to infections. Reactivation of certain viruses can lead to oral ulcers, increased common cold symptoms, or other illnesses. For example, stress can reactivate herpes simplex type 1 and interestingly, EBV.^16,17 In MS, the immune system is dysregulated and has an autoimmune component. The effect of acute emotional stress differs from that of chronic stress.¹⁸ Several studies have examined the immune responses to both forms of stress.^19-21

Interestingly, acute stress activates cell-mediated immunity, increases immune cell trafficking to areas of injury, and, importantly, increases blood-brain barrier (BBB) permeability by activating resident mast cells in the brain and other areas, including the optic nerves.^22,23 Mast cell activation leads to BBB disruption, which is a key early step in the pathogenesis of MS. Thus, it is plausible that the proinflammatory changes associated with acute stress could be implicated in the pathogenesis of MS. This contrasts with chronic stress, which attenuates various immune responses, including suppressing cell-mediated immunity, but also dysregulate the immune system.

One could establish a biological plausibility for stress playing a role in the proinflammatory responses in MS. Whether it is causal or not, scientists can further explore the potential biologic explanations. While studying the association between acute stress and MS development or disease activity is difficult, several groups have examined the potential association. Many studies, however, have limitations due to the difficult nature of studying such an association, especially in quantifying or defining acute stress in general.

A limited number of studies on MS and stress: What do we know? And what are the challenges?

Rare studies have reported a potential association between MS development and stressful life events, while others reported no association.^24-26 Also, some studies observed an increase in MS relapses or the development of new magnetic resonance imaging (MRI) lesions following stressful life events or wartime, while others failed to show such an association.^26-30 There are few studies directly addressing the potential association between acute emotional stress and MS. The results of published studies are variable, and limitations are numerous. Limitations include the difficulty in measuring acute emotional stress, difficulty in its prediction, and ethical challenges of experimental design and recruiting participants. So, studies have focused on observational aspects, retrospective reviews, and surveys of memories prone to various biases. Rarely was the design of these clinical studies prospective. A few prospective studies reported an association between stressful life events and increased MS relapses and increased number of brain lesions.^27,31,32 Rare clinical trials have attempted to test stress reduction strategies and reported on the modest improvement of patient-reported outcomes and, in one study, a modest improvement in new MRI lesions.^33-35

Overall, several lines of evidence support a potential association between acute emotional stress and MS. Yet, the association is challenging to study, and future research might focus on stress-mitigation strategies and improving coping mechanisms in persons living with MS. It is important to note that it will be very difficult to design prospective studies to examine the potential association between acute emotional trauma and the development of de novo MS. Such studies will require a large number of participants (e.g., hundreds of thousands), long durations of follow-up (e.g., decades), and ways to classify repeated stressful events. An alternative approach is to ask persons newly diagnosed with MS at the time of initial diagnosis about any temporal association between their first symptom and stressful life events. However, this approach would provide some information on any association between the two, but not on causality of the disease itself.

Conclusion

The potential association between acute emotional stress and MS dates to the times of early descriptions of MS. Yet, research has been very limited and challenging. To date, the potential association remains elusive. Lines of evidence, while with limitations, have provided possible biologic explanations for the relationship between MS symptom onset and acute emotional stress. Although avoiding acute emotional stress is nearly impossible, incorporating global stress-coping strategies in early childhood education and secondary education might theoretically have potential beneficial effects on the subsequent risk of MS development or symptom flare-up, depending on a variety of factors.

But for now, when patients and colleagues ask me, “Can acute emotional stress be a ‘trigger’ for MS symptomology?,” my answer will remain, “Potentially, until proven otherwise.”

Sir Augustus d’Este (1794-1848) described the circumstances preceding his development of neurological symptoms as follows:¹ “I travelled from Ramsgate to the Highlands of Scotland for the purpose of passing some days with a Relation for whom I had the affection of a Son. On my arrival I found him dead. Shortly after the funeral I was obliged to have my letters read to me, and their answers written for me, as my eyes were so attacked that when fixed upon minute objects indistinctness of vision was the consequence: Soon after I went to Ireland, and without any thing having been done to my eyes, they completely recovered their strength and distinctness of vision…" He then described a clinical course of relapsing-remitting neurologic symptoms merging into a progressive stage of unrelenting illness, most fitting with what we know today as multiple sclerosis (MS).¹ Why did Sir Augustus d'Este connect the event of the unexpected death to the onset of a lifelong neurologic disease?

Jean-Martin Charcot first described MS in a way close to what we know it as today. Charcot considered stress a factor in MS. He linked grief, vexation, and adverse changes in social circumstances to the onset of MS at that time.² I, as a practicing MS specialist, am surprised neither by Sir Augustus d'Este's diary nor by Charcot's earlier assessments of MS triggers.³ As I write this narrative, I think of the many times I heard from people diagnosed with MS. "It happened to me because of stress" is a statement not estranged from my daily clinical practice

MS as a multifactorial disease

It is tempting to make a case for emotional stress as a cause of MS, but one must remember that MS is a very complex disease with unclear etiologies. MS, a treatable but not yet curable disease, is the interplay between the genetics of the host and numerous environmental factors that exploit a susceptible immune system leading to unrelenting immune dysregulation.⁴ Recent studies have brought some pieces of this intricate puzzle together. The role of Epstein-Barr virus (EBV) in the pathogenesis of MS is being dissected.⁵ The possible synergy between vitamin D deficiency, EBV, and certain genetic variations is being studied.⁶ The roles of smoking, environmental toxins, obesity, diet, Western lifestyle, and the gut microbiome are some of the top areas of clinical, translational, and basic research.^7-11 But what about emotional stress? Where does it fit, if anywhere, in the current research paradigm?

Emotional stress and MS—Causality or not?

In the scientific method, several criteria must be proven for an element to be suspected in the etiology of a disease.¹² First, the suspect element must be present before the disease starts—i.e., a temporal association. Second, there must be a plausible biological explanation of how the suspect element acts in the disease's causation. Third, other variables that could confound the picture must be controlled for or dismissed. It is clear that no single factor is the cause of MS. By now, MS is agreed upon as a disease caused by multiple factors, some of which remain to be unraveled.⁹ The term "cause" has been utilized more recently by many authors when referring to EBV in relation to MS development, reasoning that in one study, in a small number of individuals with MS, EBV infection preceded the MS clinical diagnosis.¹³ Thus, the temporal association was provided. But does MS start at the onset of clinical symptoms?

For Sir Augustus d'Este, the disease may have started years before he visited the Highlands of Scotland, but only at that visit did MS become clinically apparent. So, the emotional trauma may have acted as a "trigger" for an MS flare-up rather than being a "cause" of MS. This might be a more plausible explanation of the association between emotional trauma and MS development. However, MS pathogenesis is complex, and one could argue that the disease starts many years before the first clinical symptoms that lead to diagnosis.

The MS prodrome has been demonstrated by several studies that suggest that MS may start many years before the clinical diagnosis.¹⁴ Radiologically isolated syndrome (RIS) further argues that MS may be clinically dormant for years, and clinical symptoms may not appear until later in the disease process.¹⁵ One may think that immune attacks on the optic nerves, spinal cord, or areas of the brainstem might be readily symptomatic compared to attacks on other structures of the central nervous system (e.g., periventricular or juxtacortical brain areas) that may be clinically silent. So, while for Sir Augustus d'Este it seemed that the disease started at the time of his visit to the Highlands of Scotland, it is equally plausible that it started years before the first clinical attack. Nevertheless, how could emotional stress play a role in the pathophysiology of MS?

Stress and the Immune System

At times of chronic stress, one may become more susceptible to infections. Reactivation of certain viruses can lead to oral ulcers, increased common cold symptoms, or other illnesses. For example, stress can reactivate herpes simplex type 1 and interestingly, EBV.^16,17 In MS, the immune system is dysregulated and has an autoimmune component. The effect of acute emotional stress differs from that of chronic stress.¹⁸ Several studies have examined the immune responses to both forms of stress.^19-21

Interestingly, acute stress activates cell-mediated immunity, increases immune cell trafficking to areas of injury, and, importantly, increases blood-brain barrier (BBB) permeability by activating resident mast cells in the brain and other areas, including the optic nerves.^22,23 Mast cell activation leads to BBB disruption, which is a key early step in the pathogenesis of MS. Thus, it is plausible that the proinflammatory changes associated with acute stress could be implicated in the pathogenesis of MS. This contrasts with chronic stress, which attenuates various immune responses, including suppressing cell-mediated immunity, but also dysregulate the immune system.

One could establish a biological plausibility for stress playing a role in the proinflammatory responses in MS. Whether it is causal or not, scientists can further explore the potential biologic explanations. While studying the association between acute stress and MS development or disease activity is difficult, several groups have examined the potential association. Many studies, however, have limitations due to the difficult nature of studying such an association, especially in quantifying or defining acute stress in general.

A limited number of studies on MS and stress: What do we know? And what are the challenges?

Rare studies have reported a potential association between MS development and stressful life events, while others reported no association.^24-26 Also, some studies observed an increase in MS relapses or the development of new magnetic resonance imaging (MRI) lesions following stressful life events or wartime, while others failed to show such an association.^26-30 There are few studies directly addressing the potential association between acute emotional stress and MS. The results of published studies are variable, and limitations are numerous. Limitations include the difficulty in measuring acute emotional stress, difficulty in its prediction, and ethical challenges of experimental design and recruiting participants. So, studies have focused on observational aspects, retrospective reviews, and surveys of memories prone to various biases. Rarely was the design of these clinical studies prospective. A few prospective studies reported an association between stressful life events and increased MS relapses and increased number of brain lesions.^27,31,32 Rare clinical trials have attempted to test stress reduction strategies and reported on the modest improvement of patient-reported outcomes and, in one study, a modest improvement in new MRI lesions.^33-35

Overall, several lines of evidence support a potential association between acute emotional stress and MS. Yet, the association is challenging to study, and future research might focus on stress-mitigation strategies and improving coping mechanisms in persons living with MS. It is important to note that it will be very difficult to design prospective studies to examine the potential association between acute emotional trauma and the development of de novo MS. Such studies will require a large number of participants (e.g., hundreds of thousands), long durations of follow-up (e.g., decades), and ways to classify repeated stressful events. An alternative approach is to ask persons newly diagnosed with MS at the time of initial diagnosis about any temporal association between their first symptom and stressful life events. However, this approach would provide some information on any association between the two, but not on causality of the disease itself.

Conclusion

The potential association between acute emotional stress and MS dates to the times of early descriptions of MS. Yet, research has been very limited and challenging. To date, the potential association remains elusive. Lines of evidence, while with limitations, have provided possible biologic explanations for the relationship between MS symptom onset and acute emotional stress. Although avoiding acute emotional stress is nearly impossible, incorporating global stress-coping strategies in early childhood education and secondary education might theoretically have potential beneficial effects on the subsequent risk of MS development or symptom flare-up, depending on a variety of factors.

But for now, when patients and colleagues ask me, “Can acute emotional stress be a ‘trigger’ for MS symptomology?,” my answer will remain, “Potentially, until proven otherwise.”

Sir Augustus d’Este (1794-1848) described the circumstances preceding his development of neurological symptoms as follows:¹ “I travelled from Ramsgate to the Highlands of Scotland for the purpose of passing some days with a Relation for whom I had the affection of a Son. On my arrival I found him dead. Shortly after the funeral I was obliged to have my letters read to me, and their answers written for me, as my eyes were so attacked that when fixed upon minute objects indistinctness of vision was the consequence: Soon after I went to Ireland, and without any thing having been done to my eyes, they completely recovered their strength and distinctness of vision…" He then described a clinical course of relapsing-remitting neurologic symptoms merging into a progressive stage of unrelenting illness, most fitting with what we know today as multiple sclerosis (MS).¹ Why did Sir Augustus d'Este connect the event of the unexpected death to the onset of a lifelong neurologic disease?

Jean-Martin Charcot first described MS in a way close to what we know it as today. Charcot considered stress a factor in MS. He linked grief, vexation, and adverse changes in social circumstances to the onset of MS at that time.² I, as a practicing MS specialist, am surprised neither by Sir Augustus d'Este's diary nor by Charcot's earlier assessments of MS triggers.³ As I write this narrative, I think of the many times I heard from people diagnosed with MS. "It happened to me because of stress" is a statement not estranged from my daily clinical practice

MS as a multifactorial disease

It is tempting to make a case for emotional stress as a cause of MS, but one must remember that MS is a very complex disease with unclear etiologies. MS, a treatable but not yet curable disease, is the interplay between the genetics of the host and numerous environmental factors that exploit a susceptible immune system leading to unrelenting immune dysregulation.⁴ Recent studies have brought some pieces of this intricate puzzle together. The role of Epstein-Barr virus (EBV) in the pathogenesis of MS is being dissected.⁵ The possible synergy between vitamin D deficiency, EBV, and certain genetic variations is being studied.⁶ The roles of smoking, environmental toxins, obesity, diet, Western lifestyle, and the gut microbiome are some of the top areas of clinical, translational, and basic research.^7-11 But what about emotional stress? Where does it fit, if anywhere, in the current research paradigm?

Emotional stress and MS—Causality or not?

In the scientific method, several criteria must be proven for an element to be suspected in the etiology of a disease.¹² First, the suspect element must be present before the disease starts—i.e., a temporal association. Second, there must be a plausible biological explanation of how the suspect element acts in the disease's causation. Third, other variables that could confound the picture must be controlled for or dismissed. It is clear that no single factor is the cause of MS. By now, MS is agreed upon as a disease caused by multiple factors, some of which remain to be unraveled.⁹ The term "cause" has been utilized more recently by many authors when referring to EBV in relation to MS development, reasoning that in one study, in a small number of individuals with MS, EBV infection preceded the MS clinical diagnosis.¹³ Thus, the temporal association was provided. But does MS start at the onset of clinical symptoms?

For Sir Augustus d'Este, the disease may have started years before he visited the Highlands of Scotland, but only at that visit did MS become clinically apparent. So, the emotional trauma may have acted as a "trigger" for an MS flare-up rather than being a "cause" of MS. This might be a more plausible explanation of the association between emotional trauma and MS development. However, MS pathogenesis is complex, and one could argue that the disease starts many years before the first clinical symptoms that lead to diagnosis.

The MS prodrome has been demonstrated by several studies that suggest that MS may start many years before the clinical diagnosis.¹⁴ Radiologically isolated syndrome (RIS) further argues that MS may be clinically dormant for years, and clinical symptoms may not appear until later in the disease process.¹⁵ One may think that immune attacks on the optic nerves, spinal cord, or areas of the brainstem might be readily symptomatic compared to attacks on other structures of the central nervous system (e.g., periventricular or juxtacortical brain areas) that may be clinically silent. So, while for Sir Augustus d'Este it seemed that the disease started at the time of his visit to the Highlands of Scotland, it is equally plausible that it started years before the first clinical attack. Nevertheless, how could emotional stress play a role in the pathophysiology of MS?

Stress and the Immune System

At times of chronic stress, one may become more susceptible to infections. Reactivation of certain viruses can lead to oral ulcers, increased common cold symptoms, or other illnesses. For example, stress can reactivate herpes simplex type 1 and interestingly, EBV.^16,17 In MS, the immune system is dysregulated and has an autoimmune component. The effect of acute emotional stress differs from that of chronic stress.¹⁸ Several studies have examined the immune responses to both forms of stress.^19-21

Interestingly, acute stress activates cell-mediated immunity, increases immune cell trafficking to areas of injury, and, importantly, increases blood-brain barrier (BBB) permeability by activating resident mast cells in the brain and other areas, including the optic nerves.^22,23 Mast cell activation leads to BBB disruption, which is a key early step in the pathogenesis of MS. Thus, it is plausible that the proinflammatory changes associated with acute stress could be implicated in the pathogenesis of MS. This contrasts with chronic stress, which attenuates various immune responses, including suppressing cell-mediated immunity, but also dysregulate the immune system.

One could establish a biological plausibility for stress playing a role in the proinflammatory responses in MS. Whether it is causal or not, scientists can further explore the potential biologic explanations. While studying the association between acute stress and MS development or disease activity is difficult, several groups have examined the potential association. Many studies, however, have limitations due to the difficult nature of studying such an association, especially in quantifying or defining acute stress in general.

A limited number of studies on MS and stress: What do we know? And what are the challenges?

Rare studies have reported a potential association between MS development and stressful life events, while others reported no association.^24-26 Also, some studies observed an increase in MS relapses or the development of new magnetic resonance imaging (MRI) lesions following stressful life events or wartime, while others failed to show such an association.^26-30 There are few studies directly addressing the potential association between acute emotional stress and MS. The results of published studies are variable, and limitations are numerous. Limitations include the difficulty in measuring acute emotional stress, difficulty in its prediction, and ethical challenges of experimental design and recruiting participants. So, studies have focused on observational aspects, retrospective reviews, and surveys of memories prone to various biases. Rarely was the design of these clinical studies prospective. A few prospective studies reported an association between stressful life events and increased MS relapses and increased number of brain lesions.^27,31,32 Rare clinical trials have attempted to test stress reduction strategies and reported on the modest improvement of patient-reported outcomes and, in one study, a modest improvement in new MRI lesions.^33-35

Overall, several lines of evidence support a potential association between acute emotional stress and MS. Yet, the association is challenging to study, and future research might focus on stress-mitigation strategies and improving coping mechanisms in persons living with MS. It is important to note that it will be very difficult to design prospective studies to examine the potential association between acute emotional trauma and the development of de novo MS. Such studies will require a large number of participants (e.g., hundreds of thousands), long durations of follow-up (e.g., decades), and ways to classify repeated stressful events. An alternative approach is to ask persons newly diagnosed with MS at the time of initial diagnosis about any temporal association between their first symptom and stressful life events. However, this approach would provide some information on any association between the two, but not on causality of the disease itself.

Conclusion

The potential association between acute emotional stress and MS dates to the times of early descriptions of MS. Yet, research has been very limited and challenging. To date, the potential association remains elusive. Lines of evidence, while with limitations, have provided possible biologic explanations for the relationship between MS symptom onset and acute emotional stress. Although avoiding acute emotional stress is nearly impossible, incorporating global stress-coping strategies in early childhood education and secondary education might theoretically have potential beneficial effects on the subsequent risk of MS development or symptom flare-up, depending on a variety of factors.

But for now, when patients and colleagues ask me, “Can acute emotional stress be a ‘trigger’ for MS symptomology?,” my answer will remain, “Potentially, until proven otherwise.”

The 3 “Rs” of multiple sclerosis (MS)—repair, remyelinate, and restore—spell out the goals of patients and physicians alike. MS is an incurable, immune-mediated, neurodegenerative disease of the central nervous system (CNS), and is thought to develop from unexplained autoimmune attacks directed at myelin (the covering on neurons) and glial cells, or “oligodendrocytes.” Neurodegeneration is evident early in the disease process and is characterized by mitochondrial dysfunction, energy failure, and neuronal and glial death.

While most new and investigational therapies aim to address immune dysfunction, a new idea—

one not involving immune dysregulation—is being explored in various studies: Are there agents, outside of traditional MS therapies, able to help with remyelination?

Mitochondria, oxidative stress, and MS

Neurons, oligodendrocytes, and oligodendrocyte precursor cells (OPCs) are particularly sensitive to oxidative stress. In MS, chronic inflammation and autoimmunity are key drivers of oxidative stress and secondary mitochondrial dysfunction. 

Mitochondrial dysfunction is particularly relevant for neurodegeneration in MS. The observed dysfunction includes mitochondrial DNA damage, deficiency in mitochondrial DNA repair, reduced levels of antioxidants, and increased free radicals. Furthermore, the structure and number of mitochondria temporarily increase to accommodate the increased energy needs. Despite the attempted adaptation, energy failure ultimately occurs, resulting in a mismatch between energy needs or consumption and energy production. Neuroinflammation and the imbalance between energy consumption and generation create a vicious, continuous cycle that is characteristic in progressive MS. The energy failure is then associated with neuronal death, Wallerian degeneration, and subsequent accumulation of neurologic disability. 

Current therapeutic landscape

While the therapeutic landscape for MS continues to evolve, the approved 20-plus therapies are primarily directed at the immune system. The overall goal is to modulate immune dysregulation  and decrease inflammation. Current therapies  may be able to control this macroscopic inflammatory activity. 

However, current treatments only show modest effects on disease progression, and do not help to repair neurons, remyelinate axons, or restore function that was impaired due to disease progression. Some US Food and Drug Administration (FDA)–approved therapies are thought to modulate mitochondrial functions. For example, the class of fumarates (eg, dimethyl fumarate, diroximel fumarate, monomethyl fumarate) activates the nuclear factor erythroid 2 -related factor 2 (Nrf2) pathway in treated MS patients. However, it is unclear whether activation of the Nrf2 pathway is involved in the therapeutic effects of fumarates. A recent study challenged the importance of the Nrf2 pathway as a therapeutic target for fumarates. It showed that in an MS animal model, the effects of fumarates on disease control were similar between Nrf2 knock-out mice and the wild type, suggesting that fumarates' therapeutic effects are independent of the Nrf2 pathway. Furthermore, fumarates failed to show benefits in progressive forms of MS both clinically and on a biomarker level. 

Metformin, the mitochondria, and neurodegeneration

Metformin (1,1-dimethylbiguanide) is an oral medication used primarily as first-line treatment for type 2 diabetes. However, due to its pharmacologic properties, mitochondrial effects, and the ability to cross the blood-brain barrier, scientists have shown recent interest in studying metformin in neurodegenerative diseases, including MS. Some of the potential benefits of metformin in neurodegenerative diseases include reduction of oxidative stress and countering mitochondrial dysfunction. It is known that metformin inhibits mitochondrial complex 1. Also, several studies have shown a positive effect of metformin on the reduction of oxidative stress and mitochondrial DNA regulation. Therefore, could metformin help combat mitochondrial dysfunction in MS or rejuvenate certain elements within the CNS in people with neurodegenerative diseases, including MS?

Oligodendrocytes and remyelination

Oligodendrocytes are cells responsible for myelinating axons within the CNS. Those cells originate from progenitors called OPCs. Interestingly, in humans, OPCs can mature into oligodendrocytes throughout their lifecycle, although to a much lesser extent in adults compared with children. However, therapeutic efforts to facilitate OPC maturation in vivo in MS lesions have failed thus far. Examples include high-dose biotin, the anti-LINGO-1 opicinumab, and the anticancer, retinoid-analog drug bexarotene.

So, what is behind these unfortunate failures? Some molecules (eg, biotin, opicinumab) failed to meet their clinical endpoints in randomized clinical trials, while others had severe toxicity that halted further clinical testing (eg, bexarotene). On the other hand, some molecules (eg,      clemastine fumarate), showed a modest yet promising effect on biomarkers in small clinical trials. 

A discussion on molecule failures

What could explain the failure of molecules with such promising preclinical findings? One could argue that clinical trial designs may have been insufficient to detect small remyelinating effects. One could also argue that the maturation of OPCs into oligodendrocytes is too complex to facilitate using 1 molecule that may be an inhibitor of maturation or to activate/augment a facilitator of the maturation process. There are too many natural inhibitors and facilitators of OPC maturation, and an approach with combination therapy might have a better chance at achieving a favorable therapeutic effect. 

Another piece of the complexity of OPC maturation is the recent discovery that, in humans, nonhuman primates, and other mammals, aged OPCs do not have the same capacity to mature into oligodendrocytes as young OPCs. There might be some clinical support here, as children with MS have more ability to recover from MS attacks than their adult counterparts. Also, the older the individual with MS is, the less likely they are to recover from MS attacks and the more likely they are to show signs of disease progression compared with their younger counterparts. 

Theoretically, age-related recovery from clinical attacks may be partially explained by complications due to OPC aging. To this point, can we rejuvenate OPCs and restore their ability to mature into oligodendrocytes? Can metformin be the medicine that does so? 

Interestingly, scientists could restore the ability of older OPCs to mature into oligodendrocytes, at least in the rodent model, through calorie restriction (eg, intermittent fasting) or by mimicking this state using metformin. 

Metformin and the 3 “Rs”

One idea is to use metformin to create a biochemical state that allows OPCs to regain their ability to mature into oligodendrocytes in adult or aging individuals with MS. If that is achieved, other molecules may augment OPC' maturation or inhibit OPC maturation-inhibitors and become successful in promoting remyelination. A phase 2 clinical trial in the United Kingdom that is currently recruiting participants intends to investigate a combination of metformin and clemastine fumarate in 50 patients with relapsing-remitting MS. The goal is to learn whether metformin plus clemastine allows for therapeutic remyelination. In addition, a Canadian study is investigating metformin in children with MS. Two other studies are currently recruiting to study metformin in relapsing MS (Egypt) and progressive MS (United States). 

Although testing metformin as a treatment for MS is still in the early stages, the scientific rationale is valid and supported by compelling preclinical evidence. Ongoing clinical trials will likely provide preliminary results on whether metformin will advance in clinical testing and provide clinically meaningful improvements for people living with MS.

If metformin is, in fact, a conditioning agent for use in remyelinating therapies, future clinical trials could be designed to administer metformin to rejuvenate OPCs before the administration of any molecule combination designed to facilitate OPC maturation. However, these trials will need to address an important issue: dosage. In type 2 diabetes, the typical daily dose is between 500 and 3000 mg per day. But in tests on rodents – which weigh about 10 grams – to rejuvenate OPCs, the doses of metformin were very high: 200 to 300 mg/kg. Given the body weight of humans and to avoid drug toxicity, the resulting smaller doses of metformin will take time to exert their potential therapeutic effect.
 

Should future research be successful in developing combination molecular therapies with diverse and synergistic therapeutic targets, then the 3 “Rs” in MS will allow for a fourth “R” to effectively succeed: repair, remyelinate, restore, and rehabilitate.

The 3 “Rs” of multiple sclerosis (MS)—repair, remyelinate, and restore—spell out the goals of patients and physicians alike. MS is an incurable, immune-mediated, neurodegenerative disease of the central nervous system (CNS), and is thought to develop from unexplained autoimmune attacks directed at myelin (the covering on neurons) and glial cells, or “oligodendrocytes.” Neurodegeneration is evident early in the disease process and is characterized by mitochondrial dysfunction, energy failure, and neuronal and glial death.

While most new and investigational therapies aim to address immune dysfunction, a new idea—

one not involving immune dysregulation—is being explored in various studies: Are there agents, outside of traditional MS therapies, able to help with remyelination?

Mitochondria, oxidative stress, and MS

Neurons, oligodendrocytes, and oligodendrocyte precursor cells (OPCs) are particularly sensitive to oxidative stress. In MS, chronic inflammation and autoimmunity are key drivers of oxidative stress and secondary mitochondrial dysfunction. 

Mitochondrial dysfunction is particularly relevant for neurodegeneration in MS. The observed dysfunction includes mitochondrial DNA damage, deficiency in mitochondrial DNA repair, reduced levels of antioxidants, and increased free radicals. Furthermore, the structure and number of mitochondria temporarily increase to accommodate the increased energy needs. Despite the attempted adaptation, energy failure ultimately occurs, resulting in a mismatch between energy needs or consumption and energy production. Neuroinflammation and the imbalance between energy consumption and generation create a vicious, continuous cycle that is characteristic in progressive MS. The energy failure is then associated with neuronal death, Wallerian degeneration, and subsequent accumulation of neurologic disability. 

Current therapeutic landscape

While the therapeutic landscape for MS continues to evolve, the approved 20-plus therapies are primarily directed at the immune system. The overall goal is to modulate immune dysregulation  and decrease inflammation. Current therapies  may be able to control this macroscopic inflammatory activity. 

However, current treatments only show modest effects on disease progression, and do not help to repair neurons, remyelinate axons, or restore function that was impaired due to disease progression. Some US Food and Drug Administration (FDA)–approved therapies are thought to modulate mitochondrial functions. For example, the class of fumarates (eg, dimethyl fumarate, diroximel fumarate, monomethyl fumarate) activates the nuclear factor erythroid 2 -related factor 2 (Nrf2) pathway in treated MS patients. However, it is unclear whether activation of the Nrf2 pathway is involved in the therapeutic effects of fumarates. A recent study challenged the importance of the Nrf2 pathway as a therapeutic target for fumarates. It showed that in an MS animal model, the effects of fumarates on disease control were similar between Nrf2 knock-out mice and the wild type, suggesting that fumarates' therapeutic effects are independent of the Nrf2 pathway. Furthermore, fumarates failed to show benefits in progressive forms of MS both clinically and on a biomarker level. 

Metformin, the mitochondria, and neurodegeneration

Metformin (1,1-dimethylbiguanide) is an oral medication used primarily as first-line treatment for type 2 diabetes. However, due to its pharmacologic properties, mitochondrial effects, and the ability to cross the blood-brain barrier, scientists have shown recent interest in studying metformin in neurodegenerative diseases, including MS. Some of the potential benefits of metformin in neurodegenerative diseases include reduction of oxidative stress and countering mitochondrial dysfunction. It is known that metformin inhibits mitochondrial complex 1. Also, several studies have shown a positive effect of metformin on the reduction of oxidative stress and mitochondrial DNA regulation. Therefore, could metformin help combat mitochondrial dysfunction in MS or rejuvenate certain elements within the CNS in people with neurodegenerative diseases, including MS?

Oligodendrocytes and remyelination

Oligodendrocytes are cells responsible for myelinating axons within the CNS. Those cells originate from progenitors called OPCs. Interestingly, in humans, OPCs can mature into oligodendrocytes throughout their lifecycle, although to a much lesser extent in adults compared with children. However, therapeutic efforts to facilitate OPC maturation in vivo in MS lesions have failed thus far. Examples include high-dose biotin, the anti-LINGO-1 opicinumab, and the anticancer, retinoid-analog drug bexarotene.

So, what is behind these unfortunate failures? Some molecules (eg, biotin, opicinumab) failed to meet their clinical endpoints in randomized clinical trials, while others had severe toxicity that halted further clinical testing (eg, bexarotene). On the other hand, some molecules (eg,      clemastine fumarate), showed a modest yet promising effect on biomarkers in small clinical trials. 

A discussion on molecule failures

What could explain the failure of molecules with such promising preclinical findings? One could argue that clinical trial designs may have been insufficient to detect small remyelinating effects. One could also argue that the maturation of OPCs into oligodendrocytes is too complex to facilitate using 1 molecule that may be an inhibitor of maturation or to activate/augment a facilitator of the maturation process. There are too many natural inhibitors and facilitators of OPC maturation, and an approach with combination therapy might have a better chance at achieving a favorable therapeutic effect. 

Another piece of the complexity of OPC maturation is the recent discovery that, in humans, nonhuman primates, and other mammals, aged OPCs do not have the same capacity to mature into oligodendrocytes as young OPCs. There might be some clinical support here, as children with MS have more ability to recover from MS attacks than their adult counterparts. Also, the older the individual with MS is, the less likely they are to recover from MS attacks and the more likely they are to show signs of disease progression compared with their younger counterparts. 

Theoretically, age-related recovery from clinical attacks may be partially explained by complications due to OPC aging. To this point, can we rejuvenate OPCs and restore their ability to mature into oligodendrocytes? Can metformin be the medicine that does so? 

Interestingly, scientists could restore the ability of older OPCs to mature into oligodendrocytes, at least in the rodent model, through calorie restriction (eg, intermittent fasting) or by mimicking this state using metformin. 

Metformin and the 3 “Rs”

One idea is to use metformin to create a biochemical state that allows OPCs to regain their ability to mature into oligodendrocytes in adult or aging individuals with MS. If that is achieved, other molecules may augment OPC' maturation or inhibit OPC maturation-inhibitors and become successful in promoting remyelination. A phase 2 clinical trial in the United Kingdom that is currently recruiting participants intends to investigate a combination of metformin and clemastine fumarate in 50 patients with relapsing-remitting MS. The goal is to learn whether metformin plus clemastine allows for therapeutic remyelination. In addition, a Canadian study is investigating metformin in children with MS. Two other studies are currently recruiting to study metformin in relapsing MS (Egypt) and progressive MS (United States). 

Although testing metformin as a treatment for MS is still in the early stages, the scientific rationale is valid and supported by compelling preclinical evidence. Ongoing clinical trials will likely provide preliminary results on whether metformin will advance in clinical testing and provide clinically meaningful improvements for people living with MS.

If metformin is, in fact, a conditioning agent for use in remyelinating therapies, future clinical trials could be designed to administer metformin to rejuvenate OPCs before the administration of any molecule combination designed to facilitate OPC maturation. However, these trials will need to address an important issue: dosage. In type 2 diabetes, the typical daily dose is between 500 and 3000 mg per day. But in tests on rodents – which weigh about 10 grams – to rejuvenate OPCs, the doses of metformin were very high: 200 to 300 mg/kg. Given the body weight of humans and to avoid drug toxicity, the resulting smaller doses of metformin will take time to exert their potential therapeutic effect.
 

Should future research be successful in developing combination molecular therapies with diverse and synergistic therapeutic targets, then the 3 “Rs” in MS will allow for a fourth “R” to effectively succeed: repair, remyelinate, restore, and rehabilitate.

The 3 “Rs” of multiple sclerosis (MS)—repair, remyelinate, and restore—spell out the goals of patients and physicians alike. MS is an incurable, immune-mediated, neurodegenerative disease of the central nervous system (CNS), and is thought to develop from unexplained autoimmune attacks directed at myelin (the covering on neurons) and glial cells, or “oligodendrocytes.” Neurodegeneration is evident early in the disease process and is characterized by mitochondrial dysfunction, energy failure, and neuronal and glial death.

While most new and investigational therapies aim to address immune dysfunction, a new idea—

one not involving immune dysregulation—is being explored in various studies: Are there agents, outside of traditional MS therapies, able to help with remyelination?

Mitochondria, oxidative stress, and MS

Neurons, oligodendrocytes, and oligodendrocyte precursor cells (OPCs) are particularly sensitive to oxidative stress. In MS, chronic inflammation and autoimmunity are key drivers of oxidative stress and secondary mitochondrial dysfunction. 

Mitochondrial dysfunction is particularly relevant for neurodegeneration in MS. The observed dysfunction includes mitochondrial DNA damage, deficiency in mitochondrial DNA repair, reduced levels of antioxidants, and increased free radicals. Furthermore, the structure and number of mitochondria temporarily increase to accommodate the increased energy needs. Despite the attempted adaptation, energy failure ultimately occurs, resulting in a mismatch between energy needs or consumption and energy production. Neuroinflammation and the imbalance between energy consumption and generation create a vicious, continuous cycle that is characteristic in progressive MS. The energy failure is then associated with neuronal death, Wallerian degeneration, and subsequent accumulation of neurologic disability. 

Current therapeutic landscape

While the therapeutic landscape for MS continues to evolve, the approved 20-plus therapies are primarily directed at the immune system. The overall goal is to modulate immune dysregulation  and decrease inflammation. Current therapies  may be able to control this macroscopic inflammatory activity. 

However, current treatments only show modest effects on disease progression, and do not help to repair neurons, remyelinate axons, or restore function that was impaired due to disease progression. Some US Food and Drug Administration (FDA)–approved therapies are thought to modulate mitochondrial functions. For example, the class of fumarates (eg, dimethyl fumarate, diroximel fumarate, monomethyl fumarate) activates the nuclear factor erythroid 2 -related factor 2 (Nrf2) pathway in treated MS patients. However, it is unclear whether activation of the Nrf2 pathway is involved in the therapeutic effects of fumarates. A recent study challenged the importance of the Nrf2 pathway as a therapeutic target for fumarates. It showed that in an MS animal model, the effects of fumarates on disease control were similar between Nrf2 knock-out mice and the wild type, suggesting that fumarates' therapeutic effects are independent of the Nrf2 pathway. Furthermore, fumarates failed to show benefits in progressive forms of MS both clinically and on a biomarker level. 

Metformin, the mitochondria, and neurodegeneration

Metformin (1,1-dimethylbiguanide) is an oral medication used primarily as first-line treatment for type 2 diabetes. However, due to its pharmacologic properties, mitochondrial effects, and the ability to cross the blood-brain barrier, scientists have shown recent interest in studying metformin in neurodegenerative diseases, including MS. Some of the potential benefits of metformin in neurodegenerative diseases include reduction of oxidative stress and countering mitochondrial dysfunction. It is known that metformin inhibits mitochondrial complex 1. Also, several studies have shown a positive effect of metformin on the reduction of oxidative stress and mitochondrial DNA regulation. Therefore, could metformin help combat mitochondrial dysfunction in MS or rejuvenate certain elements within the CNS in people with neurodegenerative diseases, including MS?

Oligodendrocytes and remyelination

Oligodendrocytes are cells responsible for myelinating axons within the CNS. Those cells originate from progenitors called OPCs. Interestingly, in humans, OPCs can mature into oligodendrocytes throughout their lifecycle, although to a much lesser extent in adults compared with children. However, therapeutic efforts to facilitate OPC maturation in vivo in MS lesions have failed thus far. Examples include high-dose biotin, the anti-LINGO-1 opicinumab, and the anticancer, retinoid-analog drug bexarotene.

So, what is behind these unfortunate failures? Some molecules (eg, biotin, opicinumab) failed to meet their clinical endpoints in randomized clinical trials, while others had severe toxicity that halted further clinical testing (eg, bexarotene). On the other hand, some molecules (eg,      clemastine fumarate), showed a modest yet promising effect on biomarkers in small clinical trials. 

A discussion on molecule failures

What could explain the failure of molecules with such promising preclinical findings? One could argue that clinical trial designs may have been insufficient to detect small remyelinating effects. One could also argue that the maturation of OPCs into oligodendrocytes is too complex to facilitate using 1 molecule that may be an inhibitor of maturation or to activate/augment a facilitator of the maturation process. There are too many natural inhibitors and facilitators of OPC maturation, and an approach with combination therapy might have a better chance at achieving a favorable therapeutic effect. 

Another piece of the complexity of OPC maturation is the recent discovery that, in humans, nonhuman primates, and other mammals, aged OPCs do not have the same capacity to mature into oligodendrocytes as young OPCs. There might be some clinical support here, as children with MS have more ability to recover from MS attacks than their adult counterparts. Also, the older the individual with MS is, the less likely they are to recover from MS attacks and the more likely they are to show signs of disease progression compared with their younger counterparts. 

Theoretically, age-related recovery from clinical attacks may be partially explained by complications due to OPC aging. To this point, can we rejuvenate OPCs and restore their ability to mature into oligodendrocytes? Can metformin be the medicine that does so? 

Interestingly, scientists could restore the ability of older OPCs to mature into oligodendrocytes, at least in the rodent model, through calorie restriction (eg, intermittent fasting) or by mimicking this state using metformin. 

Metformin and the 3 “Rs”

One idea is to use metformin to create a biochemical state that allows OPCs to regain their ability to mature into oligodendrocytes in adult or aging individuals with MS. If that is achieved, other molecules may augment OPC' maturation or inhibit OPC maturation-inhibitors and become successful in promoting remyelination. A phase 2 clinical trial in the United Kingdom that is currently recruiting participants intends to investigate a combination of metformin and clemastine fumarate in 50 patients with relapsing-remitting MS. The goal is to learn whether metformin plus clemastine allows for therapeutic remyelination. In addition, a Canadian study is investigating metformin in children with MS. Two other studies are currently recruiting to study metformin in relapsing MS (Egypt) and progressive MS (United States). 

Although testing metformin as a treatment for MS is still in the early stages, the scientific rationale is valid and supported by compelling preclinical evidence. Ongoing clinical trials will likely provide preliminary results on whether metformin will advance in clinical testing and provide clinically meaningful improvements for people living with MS.

If metformin is, in fact, a conditioning agent for use in remyelinating therapies, future clinical trials could be designed to administer metformin to rejuvenate OPCs before the administration of any molecule combination designed to facilitate OPC maturation. However, these trials will need to address an important issue: dosage. In type 2 diabetes, the typical daily dose is between 500 and 3000 mg per day. But in tests on rodents – which weigh about 10 grams – to rejuvenate OPCs, the doses of metformin were very high: 200 to 300 mg/kg. Given the body weight of humans and to avoid drug toxicity, the resulting smaller doses of metformin will take time to exert their potential therapeutic effect.
 

Should future research be successful in developing combination molecular therapies with diverse and synergistic therapeutic targets, then the 3 “Rs” in MS will allow for a fourth “R” to effectively succeed: repair, remyelinate, restore, and rehabilitate.

Dr. Obeidat is an Assistant Professor in the Department of Neurology, 

Neuroimmunology and Multiple Sclerosis and is the Founding Director of the Neuroimmunology and MS Fellowship Program at The Medical College of Wisconsin in Milwaukee, WI.

Dr. Obeidat reports having consulted with/spoken for/conducted clinical trials for AbbVie, Alexion, Atara Biotherapeutics, Biogen, Bristol-Myers Squibb, Central, Celgene, EMD Serono, GW Pharmaceuticals, Genentech, Horizon, Jazz Pharma, Novartis, Sanofi/Genzyme, TG Therapeutics, and Viela Bio. Dr. Obeidat serves on the editorial board of the International Journal of MS Care, the advisory board of Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS®), and the Board of Governors of the Consortium of Multiple Sclerosis Centers.

“Could multiple sclerosis be the direct result of a yet-to-be identified infection?” asked John Kurtzke, MD, of his audience during his Grand Rounds entitled “Epidemiology and the Cause of Multiple Sclerosis” at the National Institute of Health (NIH) in 2015.¹ As a pioneer of neuroepidemiology, Dr Kurtzke had long considered that infection was a key step in the development of multiple sclerosis (MS), the most disabling nontraumatic neurologic disease in young adults. He and others, from the 1970s onwards, described disease outbreaks and patterns of disease distribution in various countries during periods of immigration and even wartime.^1,2 

A half century later and Dr Kurtzke’s question has a possible answer: The Epstein-Barr virus (EBV), a gamma herpes virus responsible for mononucleosis that has been long suspected as a link to the development of MS,³ is now more than a virus of interest. A longitudinal study pinpointed the virus’ almost universal presence in patients with MS.⁴ Not everyone who develops mononucleosis from EBV develops MS, but most people become infected with EBV at some point in their lives. EBV is highly prevalent in the general population, with some studies suggesting that more than 90% of people worldwide are infected with EBV.⁵ While the discovery raises many questions about MS etiology and disease progression, it also allows discussion on more therapeutic possibilities.

MS Numbers

With nearly 1 million people in the United States living with MS, and over 2.5 million people worldwide, MS has been the subject of numerous investigations.² Its complexity and heterogeneity have gained significant interest from the scientific community, including from Dr. Kurtzke, who passed away the same year as his NIH presentation.1

Several investigators over the years have attempted to link viral infections to MS,³ especially EBV. In February 2022, a longitudinal study spanning 20 years shed additional light on this longstanding, controversial, heavily researched potential association.⁴ The collaborative group of investigators used a database of serial blood samples from more than 10 million active US military personnel to investigate the association between EBV and MS and to learn whether EBV infection preceded the development of MS. 

Out of 801 persons with a documented diagnosis of MS in this study, only 1 case occurred in a person who tested negative for EBV infection.⁴ At baseline, 35 people with MS tested negative for EBV infection, but after receiving their MS diagnosis, they tested positive for the virus,  suggesting a causal relationship between EBV and MS. The study also showed that the levels of serum neurofilament light (sNfL), a nonspecific biomarker indicative of neuroaxonal injury or degeneration, increased post-EBV infection in the sera of initially EBV-negative patients with MS.⁴ This raises the question again: Why do only a small subset of people with EBV develop MS?

Facts and Questions

MS is a complex, heterogeneous disease whose development would require more than a human gamma herpesvirus to directly trigger its life-long, unrelenting immune dysregulation in select people. The complexity, which has been reviewed in detail, 6 suggests a role for interaction between host genetics, vitamin D levels, vitamin D receptors, and a specific protein of EBV, called Epstein-Barr nuclear antigen 1 (EBNA1).6 A recent publication described the potential for molecular mimicry (also known as cross-reactivity) between (EBNA1)⁶ and a specific cell adhesion molecule expressed in glial cells of the central nervous system (GlialCAM).⁷ 

But this molecular mimicry is not sufficient to explain the EBV/MS relationship. Even in monozygotic twins, the concordance rate is around 25%, leaving three-fourths of the risk of MS to the environment and genetics-environment interaction.⁸ The chances for monozygotic twins to both be infected with EBV are estimated at much more than 25%, given the epidemiology of EBV. Thus, EBV infection combined with specific genetic susceptibility remains insufficient to explain the observed epidemiology of MS. 

More Factors

Several investigators have reported on the association between low vitamin D levels and MS. Low vitamin D is thought to affect both disease development and inflammatory activity.⁹ So, does MS result from the interaction between EBV, genetics, and low vitamin D? This interaction is plausible and is supported by several lines of evidence^.6 However, even the interaction between these 3 factors remains insufficient to explain the complexity of MS pathogenesis. 

An Unknown Mechanism

The triggering mechanism from EBV into MS remains an open question, and further research is needed. Nevertheless, if infection by EBV is a necessary, yet insufficient, step for MS to occur, can we prevent MS simply by preventing the primary EBV infection via vaccination? If so, what considerations must we make? For example, if EBV infection triggers MS via the transformation of infected memory B cells, thereby triggering an autoreactive immune response, then a vaccine capable of preventing the primary EBV infection could reduce the number of new MS cases, or ambitiously eradicate the disease itself. On the other hand, if molecular mimicry is the leading mechanism by which EBV infection triggers MS, then an EBV vaccine may have detrimental effects and theoretically trigger MS in susceptible individuals. Thus, it is of utmost importance to clearly understand how EBV infection contributes to MS pathogenesis to evaluate potential EBV vaccine candidates. 

Treatment Possibilities

What are some possible clinical implications for the EBV-MS story for people living with MS? An important consideration is whether latent EBV infection contributes to the disease process over time, or if the infection is just an initial step that triggers numerous events that then operate independently from the virus. Suppose latent EBV infection contributes to the ongoing inflammatory and neurodegenerative changes in MS. In that case, some may consider using antiviral therapies as possible therapeutics for MS (possibly as an add-on, in combination with existing or future classes of disease-modifying therapies). Other interventions targeted at infected, transformed, or autoreactive B cells may bring us closer to precision medicine in MS. On the other hand, if the role of EBV is mainly to kick off MS, then further interventions targeted at the virus may not prove to be clinically effective.

Finally, the recent evidence of possible molecular mimicry to support causality between EBV infection and MS needs further investigation to elucidate how a common, ubiquitous infection kicks off MS in selected individuals. Additionally, the complex interactions between EBV, the human immune system, and genetics, as well as with other factors such as emotional stress,¹⁰  low sun exposure,11 and other, yet-to-be-identified environmental factors, may add more pieces to the complex etiology puzzle of MS and perhaps allow for effective interventions to help reduce the incidence of MS and even modulate disease progression.

Dr. Obeidat is an Assistant Professor in the Department of Neurology, 

Neuroimmunology and Multiple Sclerosis and is the Founding Director of the Neuroimmunology and MS Fellowship Program at The Medical College of Wisconsin in Milwaukee, WI.

Dr. Obeidat reports having consulted with/spoken for/conducted clinical trials for AbbVie, Alexion, Atara Biotherapeutics, Biogen, Bristol-Myers Squibb, Central, Celgene, EMD Serono, GW Pharmaceuticals, Genentech, Horizon, Jazz Pharma, Novartis, Sanofi/Genzyme, TG Therapeutics, and Viela Bio. Dr. Obeidat serves on the editorial board of the International Journal of MS Care, the advisory board of Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS®), and the Board of Governors of the Consortium of Multiple Sclerosis Centers.

“Could multiple sclerosis be the direct result of a yet-to-be identified infection?” asked John Kurtzke, MD, of his audience during his Grand Rounds entitled “Epidemiology and the Cause of Multiple Sclerosis” at the National Institute of Health (NIH) in 2015.¹ As a pioneer of neuroepidemiology, Dr Kurtzke had long considered that infection was a key step in the development of multiple sclerosis (MS), the most disabling nontraumatic neurologic disease in young adults. He and others, from the 1970s onwards, described disease outbreaks and patterns of disease distribution in various countries during periods of immigration and even wartime.^1,2 

A half century later and Dr Kurtzke’s question has a possible answer: The Epstein-Barr virus (EBV), a gamma herpes virus responsible for mononucleosis that has been long suspected as a link to the development of MS,³ is now more than a virus of interest. A longitudinal study pinpointed the virus’ almost universal presence in patients with MS.⁴ Not everyone who develops mononucleosis from EBV develops MS, but most people become infected with EBV at some point in their lives. EBV is highly prevalent in the general population, with some studies suggesting that more than 90% of people worldwide are infected with EBV.⁵ While the discovery raises many questions about MS etiology and disease progression, it also allows discussion on more therapeutic possibilities.

MS Numbers

With nearly 1 million people in the United States living with MS, and over 2.5 million people worldwide, MS has been the subject of numerous investigations.² Its complexity and heterogeneity have gained significant interest from the scientific community, including from Dr. Kurtzke, who passed away the same year as his NIH presentation.1

Several investigators over the years have attempted to link viral infections to MS,³ especially EBV. In February 2022, a longitudinal study spanning 20 years shed additional light on this longstanding, controversial, heavily researched potential association.⁴ The collaborative group of investigators used a database of serial blood samples from more than 10 million active US military personnel to investigate the association between EBV and MS and to learn whether EBV infection preceded the development of MS. 

Out of 801 persons with a documented diagnosis of MS in this study, only 1 case occurred in a person who tested negative for EBV infection.⁴ At baseline, 35 people with MS tested negative for EBV infection, but after receiving their MS diagnosis, they tested positive for the virus,  suggesting a causal relationship between EBV and MS. The study also showed that the levels of serum neurofilament light (sNfL), a nonspecific biomarker indicative of neuroaxonal injury or degeneration, increased post-EBV infection in the sera of initially EBV-negative patients with MS.⁴ This raises the question again: Why do only a small subset of people with EBV develop MS?

Facts and Questions

MS is a complex, heterogeneous disease whose development would require more than a human gamma herpesvirus to directly trigger its life-long, unrelenting immune dysregulation in select people. The complexity, which has been reviewed in detail, 6 suggests a role for interaction between host genetics, vitamin D levels, vitamin D receptors, and a specific protein of EBV, called Epstein-Barr nuclear antigen 1 (EBNA1).6 A recent publication described the potential for molecular mimicry (also known as cross-reactivity) between (EBNA1)⁶ and a specific cell adhesion molecule expressed in glial cells of the central nervous system (GlialCAM).⁷ 

But this molecular mimicry is not sufficient to explain the EBV/MS relationship. Even in monozygotic twins, the concordance rate is around 25%, leaving three-fourths of the risk of MS to the environment and genetics-environment interaction.⁸ The chances for monozygotic twins to both be infected with EBV are estimated at much more than 25%, given the epidemiology of EBV. Thus, EBV infection combined with specific genetic susceptibility remains insufficient to explain the observed epidemiology of MS. 

More Factors

Several investigators have reported on the association between low vitamin D levels and MS. Low vitamin D is thought to affect both disease development and inflammatory activity.⁹ So, does MS result from the interaction between EBV, genetics, and low vitamin D? This interaction is plausible and is supported by several lines of evidence^.6 However, even the interaction between these 3 factors remains insufficient to explain the complexity of MS pathogenesis. 

An Unknown Mechanism

The triggering mechanism from EBV into MS remains an open question, and further research is needed. Nevertheless, if infection by EBV is a necessary, yet insufficient, step for MS to occur, can we prevent MS simply by preventing the primary EBV infection via vaccination? If so, what considerations must we make? For example, if EBV infection triggers MS via the transformation of infected memory B cells, thereby triggering an autoreactive immune response, then a vaccine capable of preventing the primary EBV infection could reduce the number of new MS cases, or ambitiously eradicate the disease itself. On the other hand, if molecular mimicry is the leading mechanism by which EBV infection triggers MS, then an EBV vaccine may have detrimental effects and theoretically trigger MS in susceptible individuals. Thus, it is of utmost importance to clearly understand how EBV infection contributes to MS pathogenesis to evaluate potential EBV vaccine candidates. 

Treatment Possibilities

What are some possible clinical implications for the EBV-MS story for people living with MS? An important consideration is whether latent EBV infection contributes to the disease process over time, or if the infection is just an initial step that triggers numerous events that then operate independently from the virus. Suppose latent EBV infection contributes to the ongoing inflammatory and neurodegenerative changes in MS. In that case, some may consider using antiviral therapies as possible therapeutics for MS (possibly as an add-on, in combination with existing or future classes of disease-modifying therapies). Other interventions targeted at infected, transformed, or autoreactive B cells may bring us closer to precision medicine in MS. On the other hand, if the role of EBV is mainly to kick off MS, then further interventions targeted at the virus may not prove to be clinically effective.

Finally, the recent evidence of possible molecular mimicry to support causality between EBV infection and MS needs further investigation to elucidate how a common, ubiquitous infection kicks off MS in selected individuals. Additionally, the complex interactions between EBV, the human immune system, and genetics, as well as with other factors such as emotional stress,¹⁰  low sun exposure,11 and other, yet-to-be-identified environmental factors, may add more pieces to the complex etiology puzzle of MS and perhaps allow for effective interventions to help reduce the incidence of MS and even modulate disease progression.

Dr. Obeidat is an Assistant Professor in the Department of Neurology, 

Neuroimmunology and Multiple Sclerosis and is the Founding Director of the Neuroimmunology and MS Fellowship Program at The Medical College of Wisconsin in Milwaukee, WI.

Dr. Obeidat reports having consulted with/spoken for/conducted clinical trials for AbbVie, Alexion, Atara Biotherapeutics, Biogen, Bristol-Myers Squibb, Central, Celgene, EMD Serono, GW Pharmaceuticals, Genentech, Horizon, Jazz Pharma, Novartis, Sanofi/Genzyme, TG Therapeutics, and Viela Bio. Dr. Obeidat serves on the editorial board of the International Journal of MS Care, the advisory board of Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS®), and the Board of Governors of the Consortium of Multiple Sclerosis Centers.

“Could multiple sclerosis be the direct result of a yet-to-be identified infection?” asked John Kurtzke, MD, of his audience during his Grand Rounds entitled “Epidemiology and the Cause of Multiple Sclerosis” at the National Institute of Health (NIH) in 2015.¹ As a pioneer of neuroepidemiology, Dr Kurtzke had long considered that infection was a key step in the development of multiple sclerosis (MS), the most disabling nontraumatic neurologic disease in young adults. He and others, from the 1970s onwards, described disease outbreaks and patterns of disease distribution in various countries during periods of immigration and even wartime.^1,2 

A half century later and Dr Kurtzke’s question has a possible answer: The Epstein-Barr virus (EBV), a gamma herpes virus responsible for mononucleosis that has been long suspected as a link to the development of MS,³ is now more than a virus of interest. A longitudinal study pinpointed the virus’ almost universal presence in patients with MS.⁴ Not everyone who develops mononucleosis from EBV develops MS, but most people become infected with EBV at some point in their lives. EBV is highly prevalent in the general population, with some studies suggesting that more than 90% of people worldwide are infected with EBV.⁵ While the discovery raises many questions about MS etiology and disease progression, it also allows discussion on more therapeutic possibilities.

MS Numbers

With nearly 1 million people in the United States living with MS, and over 2.5 million people worldwide, MS has been the subject of numerous investigations.² Its complexity and heterogeneity have gained significant interest from the scientific community, including from Dr. Kurtzke, who passed away the same year as his NIH presentation.1

Several investigators over the years have attempted to link viral infections to MS,³ especially EBV. In February 2022, a longitudinal study spanning 20 years shed additional light on this longstanding, controversial, heavily researched potential association.⁴ The collaborative group of investigators used a database of serial blood samples from more than 10 million active US military personnel to investigate the association between EBV and MS and to learn whether EBV infection preceded the development of MS. 

Out of 801 persons with a documented diagnosis of MS in this study, only 1 case occurred in a person who tested negative for EBV infection.⁴ At baseline, 35 people with MS tested negative for EBV infection, but after receiving their MS diagnosis, they tested positive for the virus,  suggesting a causal relationship between EBV and MS. The study also showed that the levels of serum neurofilament light (sNfL), a nonspecific biomarker indicative of neuroaxonal injury or degeneration, increased post-EBV infection in the sera of initially EBV-negative patients with MS.⁴ This raises the question again: Why do only a small subset of people with EBV develop MS?

Facts and Questions

MS is a complex, heterogeneous disease whose development would require more than a human gamma herpesvirus to directly trigger its life-long, unrelenting immune dysregulation in select people. The complexity, which has been reviewed in detail, 6 suggests a role for interaction between host genetics, vitamin D levels, vitamin D receptors, and a specific protein of EBV, called Epstein-Barr nuclear antigen 1 (EBNA1).6 A recent publication described the potential for molecular mimicry (also known as cross-reactivity) between (EBNA1)⁶ and a specific cell adhesion molecule expressed in glial cells of the central nervous system (GlialCAM).⁷ 

But this molecular mimicry is not sufficient to explain the EBV/MS relationship. Even in monozygotic twins, the concordance rate is around 25%, leaving three-fourths of the risk of MS to the environment and genetics-environment interaction.⁸ The chances for monozygotic twins to both be infected with EBV are estimated at much more than 25%, given the epidemiology of EBV. Thus, EBV infection combined with specific genetic susceptibility remains insufficient to explain the observed epidemiology of MS. 

More Factors

Several investigators have reported on the association between low vitamin D levels and MS. Low vitamin D is thought to affect both disease development and inflammatory activity.⁹ So, does MS result from the interaction between EBV, genetics, and low vitamin D? This interaction is plausible and is supported by several lines of evidence^.6 However, even the interaction between these 3 factors remains insufficient to explain the complexity of MS pathogenesis. 

An Unknown Mechanism

The triggering mechanism from EBV into MS remains an open question, and further research is needed. Nevertheless, if infection by EBV is a necessary, yet insufficient, step for MS to occur, can we prevent MS simply by preventing the primary EBV infection via vaccination? If so, what considerations must we make? For example, if EBV infection triggers MS via the transformation of infected memory B cells, thereby triggering an autoreactive immune response, then a vaccine capable of preventing the primary EBV infection could reduce the number of new MS cases, or ambitiously eradicate the disease itself. On the other hand, if molecular mimicry is the leading mechanism by which EBV infection triggers MS, then an EBV vaccine may have detrimental effects and theoretically trigger MS in susceptible individuals. Thus, it is of utmost importance to clearly understand how EBV infection contributes to MS pathogenesis to evaluate potential EBV vaccine candidates. 

Treatment Possibilities

What are some possible clinical implications for the EBV-MS story for people living with MS? An important consideration is whether latent EBV infection contributes to the disease process over time, or if the infection is just an initial step that triggers numerous events that then operate independently from the virus. Suppose latent EBV infection contributes to the ongoing inflammatory and neurodegenerative changes in MS. In that case, some may consider using antiviral therapies as possible therapeutics for MS (possibly as an add-on, in combination with existing or future classes of disease-modifying therapies). Other interventions targeted at infected, transformed, or autoreactive B cells may bring us closer to precision medicine in MS. On the other hand, if the role of EBV is mainly to kick off MS, then further interventions targeted at the virus may not prove to be clinically effective.

Finally, the recent evidence of possible molecular mimicry to support causality between EBV infection and MS needs further investigation to elucidate how a common, ubiquitous infection kicks off MS in selected individuals. Additionally, the complex interactions between EBV, the human immune system, and genetics, as well as with other factors such as emotional stress,¹⁰  low sun exposure,11 and other, yet-to-be-identified environmental factors, may add more pieces to the complex etiology puzzle of MS and perhaps allow for effective interventions to help reduce the incidence of MS and even modulate disease progression.