Pathophysiology of Multiple Sclerosis

Multiple Sclerosis is classified amongst the autoimmune conditions, which are diseases deriving from a malfunction of the immune system that attacks substances and tissues normally present in the body as it wrongly recognises them as foreign agents to the body system. In the case of Multiple Sclerosis the immune system attacks the nervous system.

MS Lesions

The name Multiple Sclerosis refers to lesions (also called plaques or scars) that generate in the nervous system. The majority of MS lesions are located in the white area near the cerebellum, the spinal cord, the brain stem and the optical nerve. When MS lesions are present neurons cannot transmit impulses efficiently. In fact the disease destroys the layer (myelin) which covers the nervous system’s fibres and facilitates the neurons transmitting signals to the body. This results in the diminishing or complete disappearance of myelin. A partial restorative process - called remyelination – occurs at the early stages of the disease. However, as the cells’ myelin cover cannot completely be rebuilt; repeated attacks lead to fewer successful remyelinations and thus to the formation of lesions in the irreversibly damaged areas.

Inflammation

Multiple Sclerosis also generates an inflammatory process. This inflammation is caused by the T-cells which are cells that play a crucial role in the body’s defences. In MS T-cells manage to infiltrate into the brain via the blood-brain barrier, which is both a physical barrier and system of cellular transport. This barrier is not normally accessible to T-cells, unless it is affected by a virus, which reduces the strength of the junctions forming the barrier. T-cells remain then locked inside the brain, wrongly perceiving myelin as an alien agent and attack it as if it were a virus. This generates inflammatory processes and further damaging effects such as swelling and activation of other immune cells and antibodies.