In the United States, an estimated 200 cases of multiple sclerosis (MS), an autoimmune disease, are diagnosed each week. This is according to the National Institute of Neurological Disorders and Stroke (NINDS). The disorder results from damage to the myelin sheath: a protective covering of the neuron's axons, which helps transmit signals. Patients' immune systems attack the myelin, causing it to become damaged. As a result, signals sent along neurons become disrupted, leading to the symptoms of MS.
The different types of MS vary by the presentation of symptoms. Four courses of MS exist: relapsing-remitting MS, progressive-relapsing MS, primary-progressive MS and secondary-progressive MS. The National MS Society noted that the most common type of MS is relapsing-remitting MS; about 85 percent of MS patients are originally diagnosed with this type. Patients with this presentation of MS have periods where symptoms become worse (called relapses) with alternating periods where they do not have symptoms (called remissions). The NINDS noted that patients with relapsing-remitting MS can have complete or partial remissions, though symptoms can return. The periods in which patients do not have symptoms can range from months to years. Symptoms can restart due to a trigger, such as illness, or spontaneously, according to the Merck Manual.
Some MS patients have primary-progressive MS, in which their symptoms progressively become worse and they do not experience remissions or relapses. Patients with primary-progressive MS may have periods in which they have plateaus, meaning their symptoms do not progress. The National MS Society notes that about 10 percent of MS patients have this course of the disease.
In patients who have secondary-progressive MS, they initially experience relapsing-remitting MS, then have a worsening of symptoms. The National MS Society pointed out that before disease-modifying medications were available for patients, about 50 percent of relapsing-remitting MS patients developed secondary-progressive MS within a 10 year time frame. Patients with this course of MS may or may not have any relapses.
The rarest course of MS is progressive-relapsing MS, which affects about 5 percent of patients, according to the National MS Society. With this presentation of MS, patients start with a progressive worsening, followed by sudden relapses. After these relapses, some patients may experience some recovery, but others do not. Progressive-relapsing MS progresses without periods of remission. The NINDS noted that progressive-relapsing MS, primary-progressive MS and secondary-progressive MS are sometimes grouped together under the name “chronic progressive MS.”
References
NINDS: Multiple Sclerosis: Hope Through Research
http://www.ninds.nih.gov/disorders/multiple_sclerosis/detail_multiple_sclerosis.htm
Merck Manual Home Edition: Multiple Sclerosis (MS)
http://www.merckmanuals.com/home/sec06/ch092/ch092b.html
National MS Society: What is Multiple Sclerosis?
http://www.nationalmssociety.org/about-multiple-sclerosis/what-we-know-about-ms/what-is-ms/index.aspx