Although the exact cause of multiple sclerosis (MS) is unknown, the disease is thought to occur as an immune-mediated attack on the central nervous system (CNS). The condition causes inflammation, demyelination, and axonal degeneration that can manifest through a wide variety of signs and symptoms. The age of onset for MS is usually between 15 and 50 years of age. It is the most common neurological disease causing permanent disability in young adults and is thought to affect more than 2.3 million people worldwide.
People with MS may experience paresthesias, blurred vision, optic neuritis, clumsiness, muscle weakness, cognitive decline, and urinary dysfunction. The Lhermitte sign is elicited when neck flexion produces electric shock-like sensations down the back and limbs.
There are four typical patterns of progression for MS. Clinically isolated syndrome (CIS) is the first attack of a disease that does not yet meet the full criteria for a diagnosis of MS. People who experience this episode may or may not go on to develop MS. Relapsing-remitting MS (RRMS) consists of exacerbations that alternate with full or partial recovery. This is the most common type of MS. Primary progressive MS (PPMS) is characterized by a gradual worsening of disability without remissions, although patients may experience occasional plateaus in the disease course. Secondary progressive MS (SPMS) begins with a relapsing-remitting pattern followed by a gradual worsening of neurologic function, with or without relapses.