Evidence for relative cortical sparing in benign multiple sclerosis: a longitudinal magnetic resonance imaging study

We read with interest the article of Calabrese, et al. [1]. In their MRI study, the authors found a relative cortical sparing in patients with benign multiple sclerosis (BMS), in comparison with a group of nondisabled early relapsing remitting (RR) MS. The patients with RRMS included in this study had disease duration ≤5 years and an EDSS score ≤3.0. Definition of BMS included disease duration of at least 15 years, an EDSS score ≤3.0, and the absence of cognitive impairment assessed through the Rao’s Brief Repeatable Battery (BRB) and the Stroop Test (ST). It is not fully explained whether selection of cognitively preserved patients was applied also in the recruitment of the RRMS group. Because cortical damage has been reported in association with cognitive dysfunction in RRMS [2,3], the absence of a screening for cognition in the RRMS group may lead to an overestimation of cortical lesion burden in this group. Nevertheless, this does not alter one of the main findings of this study that BMS was characterized by lower cortical pathology accumulation over time. These results add to the ongoing debate on the definition of BMS and further highlight the importance of taking into account also cognitive functioning. In a recent study, we assessed neuropsychological functioning and quantitative MR metrics in a group of 47 classically defined BMS subjects [4]. We found that the presence of cognitive impairment was related to higher lesion volumes and, in particular, higher cortical damage, as assessed by measurement of regional volumes and tissue integrity through the MT. These results were consistent with those of another recently published study in which cognitive impairment in BMS cases was associated with abnormal mean diffusivity (MD) and fractional anisotropy (FA) from both normal appearing white matter and grey matter [5]. Taken as a whole, these findings provide further evidence that benign MS is a true entity. Cognitive assessment and quantitative metrics assessing cortical and subcortical changes may help to reliably identify benign patients and to distinguish them from others MS subtypes.