Multiple sclerosis (MS) is a chronic, progressive, degenerative disorder that affects nerve fibers in the brain and spinal cord. A fatty substance (called myelin) surrounds and insulates nerve fibers and facilitates the conduction of nerve impulse transmissions.
MS is characterized by intermittent damage to myelin (called demyelination) caused by the destruction of specialized cells (oligodendrocytes) that form the substance. Demyelination causes scarring and hardening (sclerosis) of nerve fibers usually in the spinal cord, brain stem, and optic nerves, which slows nerve impulses and results in weakness, numbness, pain, and vision loss.
Because different nerves are affected at different times, MS symptoms often worsen (exacerbate), improve, and develop in different areas of the body. Early symptoms of the disorder may include vision changes (e.g., blurred vision, blind spots) and muscle weakness.
MS can progress steadily or cause acute attacks (exacerbations) followed by partial or complete reduction in symptoms (remission). Most patients with the disease have a normal lifespan.
Types
Multiple sclerosis is classified according to frequency and severity of neurological symptoms, the ability of the CNS to recover, and the accumulation of damage.
Primary progressive MS causes steady progression of symptoms with few periods of remission.
Relapsing-Remitting MS causes worsening of symptoms (exacerbations) that occur with increasing frequency, along with periods of reduced symptoms (remission).
Secondary progressive MS is initially similar to relapsing-remitting MS and eventually progresses to MS with no remission.
Relapsing-Progressive MS causes accumulative damage during exacerbations and remissions.
Incidence and Prevalence
MS is the most common neurological cause of debilitation in young people and affects about 500,000 people in the United States. Worldwide, the incidence is approximately 0.1%. Northern Europe and the northern United States have the highest prevalence, with more than 30 cases per 100,000 people.
MS is more common in women and in Caucasians. The average age of onset is between 18 and 35, but the disorder may develop at any age. Children of parents with MS have a higher rate of incidence (30–50%).