Multiple sclerosis is a chronic neurological disorder that affects the central nervous system, comprised of the brain and spinal cord. In the CNS, nerve fibers or axons are surrounded by a layer of insulation called myelin. Myelin allows nerve signals to travel properly,
In MS, the myelin is destroyed (demyelination) on the brain and spinal cord. The scarring, located at multiple sites in the CNS, disrupts transmission of messages that communicate a desired action from the brain, through the spinal cord, to various parts of the body. The inflammation produced by MS damages the axons themselves and can cause permanent loss of function. In the process, the cells that produce myelin can also be damaged. This limits the ability of the brain to repair damaged myelin.
Animation courtesy of http://www.polygonmedical.com
This is similar to a frayed electrical cord. The insulation assures that the electricity running along the wire reaches its destination without short-circuiting. In MS, the transmission along the nerve fibers “short-circuits,” becoming faulty or absent. This can cause problems with vision, coordination, sensation in the limbs, and other symptoms.
The course of the disease varies greatly from person to person. It is impossible to predict the severity or progression in any given individual. To better develop appropriate management plans, MS is divided into four classifications:
Relapsing-Remitting - clearly defined attacks lasting from days to weeks, with full recovery or with some remaining neurological symptoms and deficits upon recovery. Periods between relapses are stable and absent of disease progression. This is by far the most common form of the disease.
Secondary-Progressive – begins initially with a relapsing-remitting course that becomes consistently progressive and includes occasional relapses and minor remission. Deficits are accumulated without recovery between attacks.
Primary-Progressive – progression of level of disability from the onset without any distinct relapses of remissions. Temporary, minor improvements may be experienced.
Progressive-Relapsing – clear progression in disability level from the onset, but also clear acute relapses that may or may not include memory.
(Last reviewed 7/2009)