Associations between onset age and disability in multiple sclerosis patients studied using MSSS and a progression model

• Association between MS disability and onset age is different with symptom onset before and after an age range of 30–35 years.
• Use of progression model to measure disability produced similar results to MSSS.
• The progression model could be used as a replacement for the MSSS score if validated.

BackgroundWhile many factors have been examined, male gender and older age at multiple sclerosis onset are among few variables consistently associated with increased disability. Interestingly, the association between onset age and disability may not be linear with some data suggesting a faster rate of accumulation of disability in patients aged more than 30 years at onset.ObjectiveExplore the relationship between onset age and disability.MethodsWe studied 500 MS patients grouped by cut-offs in onset age. Disability was assessed using Multiple Sclerosis Severity Scale (MSSS) and, a model based on time to reach an Extended Disability Severity Score (EDSS) (progression model). Data were analyzed using linear and logistic regression.ResultsThe association between disability (assessed by both MSSS and the progression model) and onset age was different in patients whose MS onset occurred after an age band of 30–35 years. Before this age range, changing age was not associated with changes in disability while during and after this age range, disability was increased.ConclusionWe found a significant change in the relationship between disability and onset age after about 31 years supporting the idea that while onset age does not define a sharp cut-off, it can help define subgroups of patients with differing rates of accumulation of disability.