Multiple sclerosis (MS) is caused by inflammatory demyelination and axonal loss in the central nervous system (CNS) (brain and spinal cord). The key characteristics of the scarring (“sclerosis”) and its clinical sequelae are “dissemination in space”, affecting different anatomical sites, and “dissemination in time”, appearing episodically over time.

EPIDEMIOLOGY

Prevalence and incidence

In the UK, the prevalence is about 120/100 000 population and the annual incidence is 7/100 000 population. This means the average general practitioner may never be involved in the diagnosis of MS in their career but will have 2–4 MS patients on their list, of which 1–3 will be significantly disabled. Depending on how care is organised, up to 20% of a neurologist’s general follow-up clinic may be made up of people with MS.

Gender, age and race

• A typical patient, at the time of diagnosis, is a white woman in her 20s.

• Multiple sclerosis is three times more common in women than men, a ratio that has increased over the last century for unknown reasons.

• It usually starts in young adults—onset before puberty or after the age of 50 is rare.

• The disease is most common in White populations, especially in Northern countries.

• It is seen less frequently in Asians, except offspring of migrants who have settled in the West.

• It is occasionally encountered in the British Afro-Caribbean.

• It is very rare among the indigenous peoples of Africa and Australasia.

THE PHASES OF MULTIPLE SCLEROSIS

The natural history of three types of MS is shown in fig 1.

Relapse is a clinically evident “attack” of demyelination, characterised by gradual onset of symptoms over days, stabilising over days or weeks, and then gradually resolving, completely or partially. Different symptoms of a relapse may appear at different times: by convention, any appearing within …