How Do MS Lesions Form?

Multiple sclerosis triggers an autoimmune response that targets and damages the outer coating of the cells in the central nervous system. We explain exactly what happens each step of the way so you can better understand what's driving your symptoms. Special thanks to Lana Zhovtis Ryerson, M.D., a board certified neurologist and assistant professor in the department of neurology at NYU Grossman School of Medicine in New York City for sharing her insight and expertise for this video.

Patients with multiple sclerosis, or MS, live with scars in the central nervous system called lesions. The symptoms of MS depend on where the lesions occur in the body. Let's first explore where these lesions come from.

Everything our body does, thinking, moving, using our senses, you name it, is controlled by the central nervous system. Look closer and there are a whole lot of nerve cells or neurons. Imagine the messages sent by your brain are electrical signals. The nerve fibers on each neuron, the axons, are the wires that the brain's messages travel through. And that fatty protective layer that surrounds and insulates the nerves called the myelin sheath is like the wire coating that also helps the signals travel quickly.

Protecting the whole central nervous system is a layer of cells known as the blood brain barrier, while the immune system is the army that defends the whole body against illness. But in MS, the white blood cells, those heroic disease fighting foot soldiers, go rogue. We don't know why, but they penetrate the blood brain barrier and go after the myelin sheath on some of the neurons.

These immune cells release chemicals causing inflammation, which harms and wears down the myelin. Then other immune cells called macrophages further chew away at the myelin debris and even begin to damage the axons. This attack of healthy myelin tissue by cells that are supposed to be the good guys is the abnormal autoimmune response at the core of MS.

The name multiple sclerosis actually refers to the aftermath of these attacks. Sclerosis means scarring, which brings us back to those lesions which prevent the affected nerves from properly transmitting messages.

What's the significance of lesion location? Lesions in the brain cerebrum can compromise attention, learning, and memory. Cerebellum lesions can weaken balance and coordination. Brainstem lesions can cause double vision, facial numbness and impaired speech. Lesions on the optic nerve can blur vision and cause pain with eye movement and spinal lesions can cause muscle stiffness, numbness and tingling, arm and leg pain, and problems with urination or bowel movements.

As more lesions develop, new MS symptoms occur and eventually can even cause nerves to die and the brain to atrophy. Scars caused by MS are irreversible, but disease modifying meds can help prevent new lesions from forming, minimize symptoms, and even prevent further damage. Quality of life for MS patients has improved dramatically in the last two decades, thanks to these advances in treatment.

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