Researchers are still trying to fully understand how genetics, the environment, infections, and populations might play a role in multiple sclerosis (MS). But scientists do know that MS is a disease that stems from your immune system’s overreaction and that it attacks your own body.
MS and Your Immune System
MS happens when your immune system fails to recognize the protective coating on your nerve fibers, called myelin. Made of fat and protein, myelin encases your nerve fibers, a bit like the rubber coating on electrical wire. It helps your nerve signals travel smoothly.
With MS, your immune system sends fighter cells – mainly T cells – to attack your central nervous system, which is your brain and spinal cord. Recruiting other cells along the way, the T cells release chemicals that cause swelling and other damage to the myelin. The areas they strike are called lesions (or plaques).
This is just the start, though. This destruction tampers with the information flow between your central nervous system, or CNS, and the rest of your body. The mixed-up signals cause MS symptoms that can include numbness, weakness, and memory problems as well as affect your ability to walk, speak, or see well.
Research continues to identify all the cells involved and the triggers behind this faulty immune response.
How Mechanisms Differ for Various MS Types
There are several disease courses MS can take:
Clinically isolated syndrome (CIS). This is a first episode of symptoms, which lasts at least 24 hours. It’s caused by inflammation or myelin loss in the CNS. People who have it may or may not go on to have MS. A typical CIS case will have only one damaged area show up on an MRI. When multiple lesions appear in different areas, it’s not CIS – doctors can tell it’s happened other times. It’s a way to diagnose MS.
Relapsing-remitting MS (RRMS). RRMS is defined by attacks on myelin that cause swelling. MRIs show that people with RRMS tend to develop more new lesions due to swelling located in the brain rather than the spinal cord.
RRMS is the most common type of MS – about 85% of cases. It happens when immune cells migrate to your CNS. Spells of partial or complete recovery happen in between episodes. The disease doesn’t seem to get worse in times of remission.
Various treatments have been effective in treating RRMS. They try to limit relapses that might make new lesions. For example, if you have RRMS, your body seems to be able to restore damaged myelin through “remyelination,” especially early on. This might be how symptoms subside and go into remission. Reduced swelling might play a part, too. With primary-progressive MS (PPMS) and secondary-progressive MS (SPMS), the damage is beyond repair – this is why symptoms don’t subside or go into remission with those forms.
Primary-progressive MS (PPMS). PPMS tends to cause less swelling and fewer brain lesions than RRMS. Instead, more lesions appear in the spinal cord. PPMS doesn’t happen as much as RRMS – it makes up 10% of cases. It often starts with gradual problems with your walking.
You don’t have symptom flare-ups as with RRMS. There’s also no remission period, so your nerve function steadily gets worse. With little swelling and activity in the brain, PPMS doesn’t show up on brain MRIs, making it tricky to identify and track. A spinal cord MRI usually will show damage in about 60% of cases.
Secondary-progressive MS (SPMS). SPMS starts out as RRMS. But some people start a second phase. Their nerve function grows worse over time and progresses steadily as in PPMS. Then nerve damage or loss happens.
What Scientists Have Learned
MS reaches more parts of the brain than scientists had thought. Gray matter is the surface of the brain where cell bodies live. Axons are the parts of your nerve cells that communicate. It’s also where the lesions usually are. Axons are also white in color because they are coated with myelin. Scientists know now that MS affects all of this matter, not just where the lesion is.
MS symptoms aren’t triggered just by myelin damage. Damage to the axons, the nerve fibers, often happens before a person shows any outward MS symptoms. When cells attack the myelin, symptoms kick in.
MS activity happens even without outward symptoms. Scientists now measure disease activity by lesions that show up on your MRI – their number, size, and how inflamed they are.
New Technology and Leads
Most promising new paths for MS treatment include:
Single-cell RNA sequencing analysis lets researchers study inflammatory cells in the spinal fluid of people with MS. The tech measures the frequency of certain T cells in the spinal fluid. A treatment called B-cell depletion therapy can turn off these cells. It works well for most people, but researchers are still studying why it doesn’t work for others.
Learning from lupus. Researchers have studied a gene that’s linked to lupus, another autoimmune disease. When they studied DNA from 200 people with MS, they found the most aggressive type of progressive MS is also connected to this gene. This can show how some people might be more likely to have severe MS.
Protecting the nervous system from MS damage. This includes trying out methods that work for other disorders. Research also goes on for ways to restore myelin.
Gene chip technology, new MRI-based imaging methods, and higher-tech imaging tools let scientists see inside the lesions in the brain and spinal cord and study spinal fluid to find out how the disease process works. The goal is to stop MS from progressing, restore damage it’s caused, and end the disease.