Multiple sclerosis (MS) is a chronic, inflammatory and neurodegenerative disease in which T cells cross the blood–brain barrier and attack the myelin sheath, initiating an inflammatory cascade. The results are plaques of demyelination, gliosis and axonal degeneration.¹ It is the leading cause of non-traumatic disability among young adults, with a total estimated prevalence for the last three decades of 83 cases/100,000 population and an annual European incidence of 4.3 cases/100,000 population. The prevalence ratio of females to males is approximately 2:12 and may be increasing. The disease affects men and women in different ways, including age at onset, disease course and prognosis.³ Many geographical variations affect prevalence, including increased latitude both north and south of the equator.⁴ The onset of disease can span five decades, although it is most common between 20 and 30 years of age. The age at onset appears to affect prognosis, with younger patients generally taking longer to progress to a worse state of disability than older patients (progression to an Expanded Disability Scale Score [EDSS] of 4, at which walking is limited).⁵

MS results in significant disability: many patients are unable to walk unaided after a median of 15 years,⁶ and are wheelchair-bound by 25 years after disease onset.⁷ A number of variables have been shown topredict the time between onset of disease and onset of irreversible disability: gender, age, symptoms, disease course, degree of recovery from the first relapse, time to second neurological episode and number of relapses in the first five years of the disease. However, these variables do not influence the subsequent progression of irreversible disability.⁵ In addition to physical disability, 43% of patients have some degree of cognitive dysfunction.⁸ The social costs of MS are high and include limited ability to participate in employment and perform routine household tasks, limited social functioning and increased psychopathology.⁹ MS is also a life-shortening disease, causing an average 10–12-year reduction in life expectancy.^10,11 A study of deaths among MS patients found that complications from MS accounted for 47% of deaths, and the suicide rate was 7.5-fold higher than that for the age-matched general population.¹²

The clinical course of MS is heterogeneous, with variability both between and within patients, and has been categorised as secondary progressive MS (SPMS), primary progressive MS (PPMS) or relapsing– remitting MS (RRMS); the latter accounts for 85% of MS patients in the initial disease course. This article will focus on RRMS, which is characterised by relapses during which new symptoms may occur and old ones worsen, and remissions during which the patient fully or partially recovers from the deficits acquired during the relapse.¹³

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