Isolated cognitive relapses in multiple sclerosis.

Abstract

While cognition can be affected during sensorimotor multiple sclerosis (MS) relapses, the relevance of isolated cognitive relapses (ICRs ie, those occurring in absence of new sensorimotor symptoms) remain poorly characterised. Here, we decided to explore the relationship between ICR, subjective evaluation of cognitive performance and long-term cognitive decline in a group of subjects with relapsing-remitting MS. We analysed the cognitive performance of 99 clinically stable relapsing-remitting MS for whom data from four consequent clinical and cognitive evaluations were available, that is, a baseline evaluation (t₀), followed in the subsequent 6 months by a second evaluation performed not later than 2 weeks after a routine brain scan positive for at least one area of gadolinium enhancement (t₁) and two gadolinium enhancement-negative follow-up evaluations after 6 months (t₂) and 1 year (t₃) from t₁. Based on published literature, we defined as a meaningful change in cognition a transient reduction of Symbol Digit Modalities Test score of at least four points at t₁ compared with t₀ and t₂. ICRs were found in 17 patients and were not associated with subjective cognitive deficits or depression. Subjects who presented with an ICR at t₁ presented with a significantly reduced cognitive performance at the follow-up evaluations compared with patients without ICR. We showed that ICRs were not associated with changes in mood, fatigue levels or cognitive performance self-evaluations. Our study introduces an operational definition of ICRs and suggests to their role as a factor for cognitive decline in MS.