What is Multiple Sclerosis?

Multiple sclerosis (MS) is a chronic auto-immune neurological disease characterised by damage to the myelin coating of nerve cells in the brain, spinal cord and the central nervous system (CNS). MS affects individuals of all races and socio-economic groups. A description of why myelin is important in the central nervous system and the consequences of demyelination is provided in the link at the bottom of this page.

The cause of MS is unknown but the disease involves an autoimmune response, in which cells of the immune system attack and destroy the myelin sheath. The course of the disease is highly variable. It is generally not fatal and many people with MS lead normal lives although as the condition progresses some adjustments may be necessary.

MS begins with lesions or patches in the CNS where inflammation has resulted in the loss of myelin, a fatty insulation covering nerve fibres, in a process called demyelination, resulting in multiple patches of hard, scarred tissue called plaques. Some lesions will repair themselves while others become permanent areas of visible scarring.

As well as the process of demyelination, which causes MS relapses and symptoms, research also suggests that widespread nerve fibre damage may occur from the initial stages of the condition and this may be responsible for the progressive disability which some people with MS experience.

Diagram representing the different types of multiple sclerosis

Generally MS is grouped into four main types:

1. Relapsing-remitting MS:
   Most people are first diagnosed with the relapsing remitting form. This means they experience a relapse or flare up of symptoms (also known as an attack or exacerbation) followed by remission (a period of recovery).
2. Secondary progressive MS:
   Most people who start out with relapsing remitting MS later develop a form that is known as secondary progressive MS. In this form, symptoms do not go away completely after a relapse and there is a steady increase in disability. To determine if a person has moved from relapsing remitting to secondary progressive MS, they must have shown a continued deterioration for at least six months, whether they continue to have relapses or not. On average 65% or people with relapsing remitting MS will have developed secondary progressive MS within 15 years of diagnosis.
3. Benign MS:
   People with relapsing remitting MS who only have a small number of relapses, followed by a complete recovery, may be described as having benign MS. It is only possible to make a diagnosis of benign MS once a person has experienced little or no disability for a period of 10 to 15 years. However, a diagnosis of benign MS does not mean that they will be free of problems; a relapse may occasionally occur after many years in which MS has been inactive.
4. Primary progressive MS:
   This is a relatively unusual form of MS which tends to be diagnosed in older people, usually in their forties or later. From the outset, those with primary progressive MS experience steadily worsening symptoms and an increase in disability. Symptoms may level off at any time, or may continue to worsen. Approximately 10 to 15% of people with MS have the primary progressive form. Unlike relapsing remitting MS, men are just as likely to develop this type as women.

Click on the links for details of:

• What is Myelin?
• Relapses of Multiple Sclerosis
• Progression of Multiple Sclerosis
• Prevalence of Multiple Sclerosis

Amended April 2008