Multiple sclerosis (MS) is a progressive, degenerative condition that affects nerve fibers in the brain and spinal cord. MS is thought to be an autoimmune disease, meaning the immune system attacks parts of the body as if they were foreign. In this case, the body attacks myelin, a fatty substance that surrounds and insulates nerve fibers and allows for nerve impulse transmission. In cases of MS, the patient’s myelin is damaged in a process called demyelination, causing the scarring of hardening of nerve fibers in the spinal cord, brain stem and optic nerves, thus slowing nerve impulses and resulting in weakness, numbness, pain and vision loss.
Different nerves are affected at different times, so MS symptoms can worsen, improve and develop in different parts of the body. The condition can progress steadily or cause acute attacks followed by remission. Multiple sclerosis affects between 250,000 and 500,000 people in the United States and as many as 2.5 million worldwide, with the highest prevalence in Northern Europe and the northern part of the United States. The condition affects two to three times more women than men, and Caucasians more than members of other races. Most of these individuals will have normal lifespans; however, the severity of the condition varies significantly. For some, MS will be a relative mild ailment, while for others it can lead to permanent disability.
There are four types of multiple sclerosis. These are classified based on the severity and frequency of neurological symptoms, the accumulation of damage and the ability of the central nervous system to recover.
- Progressive primary MS: Individuals with this type of MS have a steady progression of symptoms with few periods of remission. Symptoms get worse over times, without relapses or remissions. This type is usually diagnosed in people over the age of 40.
- Relapsing-remitting MS: Patients with this type of MS experience symptoms that come and go—they can evolve over the few days and then disappear. On average, relapses appear every two years, though the period between relapses can be as long as 20 years or more. Some individuals even experience just one attack during their entire life. This is the most common form of the illness, affecting up to 80 percent of individuals diagnosed with multiple sclerosis. Roughly have of patients diagnosed with relapsing-remitting MS will develop secondary progressive MS within the first 10 years after diagnosis. It is most often diagnosed when the patient is between the ages of 20 and 40.
- Secondary progressive MS: This type of multiple sclerosis is initially similar to relapsing-remitting MS, but eventually progresses into MS without remission in about five to 15 years after the disease begins. Neurological symptoms progressively worsen, though over time, it is common for these patients to have fewer or even no attacks even while the disease progresses. About 30 percent of MS patients have secondary progressive MS.
- Relapsing-progressive MS: This rare form of MS is characterized by a gradual worsening of symptoms from the outset, with some relapses and remissions.