MS The Disease
What is Wrong in Multiple Sclerosis?
In people with MS, there are three processes going on that normally do not occur in healthy people. First, tiny patches of inflammation occur in the brain and spinal cord. Second, the protective myelin coating around the axons starts to deteriorate (this is called ‘ demyelination’). Third, the axons themselves may be damaged or destroyed.
These processes are never the same in any two people with MS. When, how quickly and to what extent they occur varies a great deal.
Inflammation in the CNS
The brain and the nervous system are nourished by tiny blood vessels, capillaries. The brain and nervous system are also protected by the blood-brain barrier, an envelope of tightly packed cells that prevents everything except oxygen and nutrients passing over from the blood (refM4). Sometimes this barrier breaks down and other molecules, such as antibodies and even cells, can cross the barrier.
T-cells are key members of the body’s immune system. In MS abnormally functioning T-cells leak out of the blood vessels and cause swelling and damage (inflammation) in the white matter (myelin).
Demyelination
For reasons not clearly understood, the T-cells produce chemicals that attack and break down the myelin sheath of the axons. Both the myelin and the cells that produce myelin are attacked (refM5). This process is called an ‘autoimmune reaction’, because the body is attacking itself (‘auto’ means ‘self’). Click here for more information on autoimmune diseases.
When this ‘demyelination’ (ie damage to the myelin) happens, the passage of information and instructions through electrical signals that travel along the axons is inhibited. When the damage becomes significant, persons with MS experience typical symptoms: poor muscle coordination, numbness or tingling, weakness and fatigue and other problems.
The Cycle of Damage and Recovery
Once the inflammation within the CNS subsides, cells within the CNS begin to repair the damaged myelin. This process is called ‘remyelination,’ or restoration of the myelin.
This cycle of damage and recovery occurs over and over again in the myelin, often unnoticed, especially in the early stages of the disease. When, and to what extent, symptoms become apparent depends on the location, extent and severity of inflammation. If the inflammation occurs repeatedly in the same place, the repair processes may not be able to ‘keep up', and permanent damage to the axons may occur. When the inflammation covers a large area, it can often leave a scar, known as a ‘ plaque’ or an area of sclerosis in the CNS that can be identified with a magnetic resonance imaging (MRI) scan.
Axonal Injury
Another factor that contributes to the progress of MS is a process called ‘axonal loss’. Axons exposed by demyelination may become so badly damaged that they break - this is known as 'axonal transection'. When this happens it means that the passage of electrical signals is completely lost and cannot be restored. Axonal loss might occur very early in the course of the disease, even before visible symptoms of MS appear.
Experts believe that permanent disability in MS could be the result of both ongoing demyelination and axonal injury.