Is Multiple Sclerosis an Autoimmune Disease? We Asked the Experts
Multiple sclerosis is a chronic disease where your immune system starts attacking your brain and spinal cord. The number of people living with the condition has grown to 913,925—current estimates report more than twice as many people are living with multiple sclerosis than previously expected.
If not properly treated, multiple sclerosis can limit a person’s physical abilities and make it difficult to work or continue pursuing fun and relaxing activities. Research into multiple sclerosis has investigated the reason behind the immune system’s sudden revolt against the body. While scientists have made headway into several theories—viruses, genetics, vitamin D levels—the true cause remains unknown.
Neurologists and autoimmune experts have debated whether multiple sclerosis can even be considered an autoimmune disorder, arguing that it could possibly be a neurodegenerative disorder instead. Without a complete understanding of the disease, it may take decades before we’ll finally see a cure for multiple sclerosis.
What we know: How multiple sclerosis affects the nervous system
No one knows why your immune system suddenly flips like a switch, branding your own cells an enemy of the state. In multiple sclerosis, the immune system attacks a white layer wrapped around each nerve cell called the myelin sheath. The myelin sheath works like a sleeve similar to the coating surrounding an electrical wire. Not only does it protect the nerves from damage, but it acts as an insulator to speed up the electrical activity neurons use to communicate with each other.
When immune cells attack and destroy the myelin sheath, your nerves will have trouble talking with others and relaying signals to the rest of the body. Jeffrey Kane, M.D., a pediatric neurologist at Pediatrix Child Neurology Consultants of Austin, explains that an attack on the myelin sheath affects nerve function causing clinical episodes where part of your brain or spine temporarily stops working. “You might get weak on one side of your body, or you might lose sensation, and your feet become unsteady. Those are kind of typical symptoms depending on where in the brain.”
Kane says people who experience these initial attacks often go on to make a full recovery. The issue becomes when these attacks are recurring. Frequent attacks can, over time, make the disability permanent.
“Before we had the treatments we have now, most people with multiple sclerosis would have wound up permanently disabled,” says Kane. “It’s not usually life-threatening, but people would be in wheelchairs, or they would have repeated hospitalizations that include vision loss.”
What we know: There is more than one version of multiple sclerosis
One person’s multiple sclerosis can look widely different from another. While the most common symptoms are muscle weakness and vision loss, others may show extreme fatigue, slurred speech, or bladder issues. It depends on what area of the brain or spinal cord the immune system is attacking.
“The course is very unpredictable and varies widely between patients,” explains J. William Lindsey, M.D., director of multiple sclerosis at UTHealth Houston and neurologist at Memorial Hermann. While multiple sclerosis can happen at any moment, Lindsey says it usually starts in young adults between their 20s and 40s.
There are four disease courses of multiple sclerosis. Each carries its own risk of disability, disease severity, and relapse.
Clinically isolated syndrome: The first time you experience one or more neurological symptoms. It lasts for at least a day and is caused by damage to the myelin sheath. If the clinically isolated syndrome is associated with brain lesions, there is a 60% to 80% chance of the episode progressing towards multiple sclerosis in a few years.
Primary-progressive multiple sclerosis: A version of multiple sclerosis where your neurologic function worsens over time without any early remission or relapse. Because of the severity and frequency of the symptoms, people with primary-progressive multiple sclerosis tend to have more disabilities, especially with walking. Compared to other multiple sclerosis types, attacks on the central nervous system tend to happen more in the spinal cord than in the brain.
Relapsing-remitting multiple sclerosis: The most common type of multiple sclerosis where people experience recurring relapses where new symptoms appear and worsen along with temporary remissions where symptoms begin to resolve.
Secondary-progressive multiple sclerosis: This disease course comes after relapsing-remitting multiple sclerosis. In this scenario, a person continues to have worsening neurologic disability because of the extensive damage to nerve cells but fewer relapses.
What we don’t know for sure: Whether multiple sclerosis is potentially a neurodegenerative disease
Benjamin Greenberg, M.D., an autoimmune disorders expert at UT Southwestern Medical Center, points out that multiple sclerosis does not technically follow the criteria for autoimmune disease.
The debate first arose in the early 2000s; an opinion piece published in Current Opinion in Neurology argued that the progressive disease phase of multiple sclerosis closely resembles neurodegeneration rather than the after-effects of immune damage. Another article published in 2008 argued that without knowing the exact cause of multiple sclerosis, scientists are not able to rule out neurodegeneration as a potential reason why irreversible neurological disability. “There are elements of the condition that suggest they are independent of autoimmunity,” explains Greenberg. “This can be a component of neurodegeneration when neurons start to die, and whether or not this is triggered by an autoimmune event or not can start a ‘fistfight’ at a [multiple sclerosis] conference.”
A 2012 review published in Autoimmune Diseases suggests that multiple sclerosis is immune-mediated but not a classical autoimmune disease as it might be the effects of an infectious virus or bacteria. They argue that for systemic autoimmune diseases, where a condition impacts multiple tissues and organs, there needs to be an autoantigen. An autoantigen is a protein or DNA fragment that the immune system mistakenly targets as a foreign invader to the body. Greenberg says that no scientist, as of yet, has identified even a single autoantigen for multiple sclerosis.
What we don’t know for sure: What type of disease is multiple sclerosis
The general consensus in the medical community is that multiple sclerosis is an autoimmune disease. He argues that the criteria for autoimmune disorders is outdated. “The dogma is that autoimmune diseases have to have a single antigen. But we have evidence to say that may not be the case. You can have autoimmune diseases where more than one antigen is potentially important,” explains Greenberg. “Our lack of understanding of each step in the immune system’s damaging pathway opens the door for this type of debate because we can’t point to a single antigen.”
Lindsey adds that conditions, such as rheumatoid arthritis, are accepted as an autoimmune disease despite not knowing the exact antigen. For multiple sclerosis, “there’s been a lot of [antigens] that have been proposed, but we don’t have a generally agreed on autoantigen. We’re still actively looking for that.”
If the definition of an autoimmune disease was to be expanded, multiple sclerosis experts suggest it signifies any abnormal immune system that is attacking and damaging its own body.
However, despite the revision, Greenberg says that doctors need to acknowledge that there might be more to the story than just a faulty immune response.
“Multiple sclerosis is a mystery I believe we are going to solve in terms of cause and underlying biology of the disease,” adds Greenberg. “We’ve gained a lot of ground in understanding it over these last several decades. It’s just a matter of time before we get the final answers.”
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