Age at onset as a determinant of presenting phenotype and initial relapse recovery in multiple sclerosis.

BACKGROUND: Age at onset modifies prognosis in multiple sclerosis (MS) and may also exert an effect on the characteristics of disease ignition. Understanding how age influences presentation informs disease management and may allow differentiation of distinct clinical sub-groups.
OBJECTIVES: To determine the nature of age-specific presentations of relapsing-remitting MS (RRMS) with respect to onset symptoms, gender ratios and index event outcomes.
METHODS: In a prospective, population-based sample of 1424 patients in South-East Wales we examined associations between age at onset, clinical features and outcome of the onset event, making specific comparisons between paediatric, adolescent and late-onset MS.
RESULTS: Age at onset varied significantly between sexes (Male 31.2, Female 29.3, p = 0.002), 0.7% had paediatric onset, 2.7% adolescent onset and 2.8% late-onset MS (>50 years). Optic neuritis was common in younger patients and declined after age 30. Lower limb motor, facial sensory, sexual and sphincteric symptoms rose with age independent of sex and disease course. F:M ratios were highest <16 years of age and declined with increasing age, with a male excess in those over 50. Probability of complete recovery from index event declined with age from 87.4% in the youngest group to 68% in the eldest (p = 0.009).
CONCLUSIONS: Age at disease onset in RRMS exerts a significant effect on gender ratios and presenting phenotype, and allows identification of specific clinical sub-groups. In addition, ability to recover from initial relapse declines with age, suggesting accumulation of disability in MS is an age-dependent response to relapse.