Clinical characteristics of progressive relapsing multiple sclerosis

Objective: Patients with progressive relapsing (PR) multiple sclerosis (MS) may accrue disability by incomplete recovery from acute exacerbations and by ongoing deterioration. In primary progressive (PP) MS, disability accumulates solely by continuous decline. Because it is the least common form of MS, there is scant information regarding the clinical characteristics of PRMS, but relapses are reportedly uncommon. The purpose of this study is to describe the clinical features of a cohort of patients with PRMS. Methods: A retrospective chart review of 16 patients diagnosed with PRMS at two academic MS centres over a four-year period. Results: Nine men and seven women had PRMS. The mean age at onset was 35.1 ± 11.2 years. The most common presenting symptom was a progressive myelopathy. The mean disease duration was 10.1 ± 8.5 years and the average time to first exacerbation was 4.1 ±3.7 years. Patients had an average of 2.8 ± 2.3 relapses with an annualized relapse rate of 0.6 ± 0.8. Time to Expanded Disability Status Scale (EDSS) 6.0 was strongly associated with time to first exacerbation. Although there was no correlation between the number of relapses and time to EDSS 6.0, there was a modest inverse relation between time to EDSS 6.0 and annualized relapse rate. Conclusions: Relapses in PRMS may occur more often than previously described and disability may accumulate more rapidly in PRMS than in PPMS. We suggest differentiating between these two forms of MS.