Multiple sclerosis

The axons of many large neurones in the central nervous system- the brain and spinal cord are ‘myelinated’. That is, they are coated with a fatty substance that helps to insulate the axon, and speed up impulses travelling its length.

Small gaps between myelin along the length of an axon are called nodes of Ranvier. The signal leaps between the nodes making the journey from the cell body to the axon terminals faster still.

Multiple sclerosis (MS) is an auto-immune disease. That is, one in which the immune system attacks part of its own body, mistaking it for a harmful ‘foreign’ substance that should be defended against. In multiple sclerosis, often the activity of the immune system is ‘switched on’ due to an infection of some kind, such as a common cold or influenza. As the body recovers, the immune system should ‘switch off’- but in MS this doesn’t happen, for reasons not well understood. The immune system attacks myelin in patches, in the brain and spinal cord.

Symptoms depend on the functions of the areas of brain or spinal cord affected, and can be mild or severe. Tiredness or worse, fatigue are fairly common in MS, as is visual disturbance. Strange tingling or other sensations in limbs often occur. In more severe MS, the ability to walk and generally control limb movement are impaired.

Myelin has capacity to self-repair, so in some cases, there may be spells of severe symptoms and other spells of temporary recovery. This disease trajectory is known as ‘relapsing and remitting MS’. In other cases the disease is continually progressive- there are no recovery spells, the disease is progressively debilitiating and leads to early death often from eventual loss of ability to swallow, causing aspiration pneumonia (drinks and food are inhaled and collect in the lungs). This is a rarer form of MS thankfully. In contrast, many people have fairly mild symptoms, that do not worsen, and life expectancy is no different to that of the wider population.

There is no cure for MS currently, but treatments can alleviate symptoms.