What Happens in MS

Recurring episodes of MS can cause many scars to appear in the central nervous system resulting from the breakdown of myelin, the insulating material that covers the nerve fibres. This can result in impairment of motor, sensory and cognitive functions to a greater or lesser extent.

MS is considered to be an autoimmune disease in which the body’s immune system mistakenly attacks normal tissue in the body. Research to date suggests that this attack is primarily aimed at myelin, an important substance in the central nervous system (CNS), and the oligodendrocyte cells that are responsible for making and maintaining myelin.

The CNS includes the brain, optic nerves and spinal cord, which are made up of nerves (bundles of nerve fibres) that act as the body’s messenger system. Each nerve fibre has a fatty covering of myelin (white matter) that serves as insulation, much like the plastic coating on an electrical wire. This helps the efficient transmission of nerve impulses (messages) between the brain and other parts of the body.

In MS, a process called demyelination causes scar tissue or sclerotic plaques (lesions) to form along the myelin sheath. These interfere with the conduction of nerve impulses within the CNS, which causes the symptoms people may experience over the course of MS.

In addition to demyelination, research indicates that damage may also occur to the nerve fibres (axons) themselves. Because this damage is seen in active, inflammatory lesions, researchers have suggested that the immune attack in MS may also target nerve cells directly, not just the myelin and oligodendrocyte cells. Evidence further indicates that this damage may occur early in the course of MS, reinforcing the importance of early treatment.

Since demyelination occurs randomly throughout the CNS, a wide range of symptoms can occur.