Brain Primer

Multiple Sclerosis: When the Immune System Attacks the Nervous System

  • Reviewed21 Aug 2023
  • Author Gail Zyla
  • Source BrainFacts/SfN
Multiple Sclerosis via Lightspring

As of 2023, 2.9 million people around the world live with multiple sclerosis (MS): an inflammatory, autoimmune disease of the central nervous system commonly diagnosed in people between 20 and 40 years of age. For unknown reasons, the immune system of a person with MS launches an attack against its own central nervous system, including the brain, spinal cord, and optic nerves. The target of this attack is the myelin, a fatty substance that forms a protective coating around nerve fibers; the nerve fibers themselves can also be affected. As a result of the attack, the damaged myelin sheath and accompanying inflammatory cells form lesions, patches of scar tissue that look like sclerosis.

In MS, the patches of disease activity appear in multiple areas of the central nervous system, which is why the disease is called multiple sclerosis. Damage to the myelin sheaths and nerve fibers interferes with transmission of nerve impulses within the brain and spinal cord, as well as their communication with other body areas. The effects of MS are often compared to the loss of insulation around an electrical wire and damage to the wire itself, interfering with signal transmission. Damage can occur in the white (myelin) and gray (nerve cell bodies, glia, etc.) matter of the brain. 

Damage to the nervous system in people with MS can cause a wide array of symptoms. The spinal cord, cerebellum, and optic nerve are commonly affected by MS, so problems often arise in functions controlled by those areas. Symptoms include numbness, clumsiness, and blurred vision. Other symptoms are slurred speech, weakness, pain, loss of coordination, uncontrollable tremors, loss of bladder control, memory loss, depression, and fatigue.

The cause of MS is unknown, but there are some hints that genetic factors, environmental factors, and certain viruses are involved. Siblings of people with MS are 10 to 15 times more likely to develop MS than people with no family history of the disease. The risk is particularly high for an identical twin of someone with MS. Oddly, the disease is more prevalent in temperate climates, such as the northern United States and northern Europe, than in the tropics. Although Caucasians run a higher risk than other races of developing MS, the prevalence of MS indicates that risk is shaped by both genetic and geographical factors. Several studies have shown that those who spend more time in the sun and have relatively higher levels of vitamin D are less likely to develop MS, possibly through UV light’s impact on the immune system and through vitamin D’s impacts on immune system regulation.

Additionally, people who develop an exaggerated immune response to certain viruses like the Epstein-Barr virus (EBV) — the virus that can cause infectious mononucleosis, or mono — may have a higher likelihood of developing MS in the future. Although EBV eventually infects around 95% of adults, very few will develop MS.

When a person is diagnosed with MS, treatment options depend on the type of disease that is present. Specialists classify MS as one of four categories: 

  1. clinically isolated syndrome, referring to a first episode of neurologic symptoms caused by inflammation and demyelination;
  2. relapsing-remitting MS, characterized by flare-ups of new or worsening symptoms followed by complete or partial remission of symptoms;
  3. primary-progressive MS, defined by progressive worsening of symptoms after disease onset;
  4. and secondary-progressive MS, in which relapsing-remitting disease has transitioned into a progressive form of disease that worsens over time.

Within each of the three latter categories, MS is further classified as “active” or “not active.” While the categories refer to the progression of symptoms, this classification refers to presence (“active”) or absence (“not active”) of a clinical relapse or new areas of inflammation that can be seen on MRI scans. In some cases, MS is defined as “stable,” meaning that symptoms are stable, and no activity appears on routine MRI scans.

MS has no cure, but an increasing number of medications are becoming available or are under investigation. Several medications help control the inflammation and immune system attacks in relapsing-remitting MS with variable response rate. Some medications are highly effective in controlling inflammation but are less effective in controlling disease progression. Steroid drugs, specifically glucocorticoids, reduce the inflammation and might also help shorten acute attacks. Medications and therapies are also available to control symptoms such as muscle stiffness, pain, fatigue, mood swings, and bladder, bowel, or sexual dysfunction.

Adapted from the 8th edition of Brain Facts by Gail Zyla.



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