Multiple sclerosis (MS) is a neurodegenerative disorder caused by the immune system mistakenly attacking the myelin sheath, a protective coating around nerve fibers. This results in inflammation, which further damages the myelin sheath, as well as the nerve cells themselves and the cells that produce myelin.
The immune system attack on myelin causes a disruption in electric signals traveling along the nerve fibers from the brain to the body and back. As a result, patients with MS experience many symptoms, including fatigue, numbness and tingling, muscle spasms, walking difficulties, pain, and bowel or bladder problems. Many patients also experience emotional changes, including depression, anxiety, and mood swings.
In some patients, the misled immune response causes disease relapses, or periods in which one or more symptoms appear or get substantially worse, followed by periods of partial or complete recovery from symptoms. In others, symptoms steadily worsen over time, with or without the presence of relapses.
There is no single test to diagnose MS. Physicians diagnose the disease based on a series of physical and neurological examinations that can help eliminate other conditions.
These tests include magnetic resonance imaging that looks for damage in the central nervous system (the brain and spinal cord), and blood and cerebrospinal fluid tests to detect inflammation and specific biomarkers of disease. Evoked potential tests that measure electrical signals from the brain are also frequently used to determine if the speed of electric impulses is impaired.
Patients with MS are broadly classified into four groups based on disease progression.
Clinically isolated syndrome
Clinically isolated syndrome represents a single event, the first episode of neurological symptoms that typically precedes relapsing forms of MS. On its own, a single event is not enough to define MS, unless patients have evidence of several lesions in their brains. That’s what the “multiple” refers to in “multiple sclerosis.”
Relapsing-remitting multiple sclerosis
Relapsing-remitting multiple sclerosis (RRMS) is the most common type of MS. Patients experience attacks of increasing neurological symptoms, called exacerbations or relapses, followed by periods of partial or complete recovery, called remissions. At various times, patients may have active, not active, or worsening neurological symptoms.
Secondary progressive multiple sclerosis
Secondary progressive multiple sclerosis is the secondary stage of MS that follows RRMS. Patients may have relapsing-remitting episodes initially, but then they experience a steady worsening of neurological symptoms over time that may be accompanied by occasional relapses.
Primary progressive multiple sclerosis
Primary progressive multiple sclerosis (PPMS) affects about 15% of MS patients. Instead of periods of relapses followed by remission, people with PPMS experience a steady decline in neurological function without relapses from the onset of symptoms.
Many treatments are available for MS, with many more experimental ones being developed. Most therapies seek to suppress the immune system to reduce inflammation and help protect the myelin sheath.
People with MS typically live for several decades following their diagnosis. With improving treatments, life expectancy for patients has increased over the years, and most now live into their 70s.
Last updated: July 1, 2021
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