Benign multiple sclerosis: a new definition of this entity is needed

Background: To study a cohort of benign multiple sclerosis (BMS) patients beyond physical disability, including the evaluation of cognitive and social function, as well as fatigue, pain and MRI studies. Methods: A cohort of 342 patients was prospectively followed for 10.9 +/- 0.71 years. Forty-three patients (12.5%) met the BMS diagnosis criteria [Expanded Disability Status Scale (EDSS) < 3 after at least 10 years' disease duration], undergoing full neurological examination every 6 months. Neuropsychological status, pain, fatigue, social functioning and work-related disability, as well as brain MRIs, were assessed yearly. Results: By the end of follow-up, 20 of 43 BMS patients (47%) had suffered cognitive impairment and 23 (53.3%) referred depression. Furthermore, 21 (48.8%) reported significant changes in pain intensity, with fatigue and environmental severity scores significantly increasing over time in 33-35% of patients. Finally, 32 BMS patients (74%) showed significant increase in the number of new or enlarging T2 lesions, gadolinium-enhanced lesions, and persistent black holes, without changes in EDSS. Thirty-five of 43 patients (81%) fulfilling the BMS diagnostic criteria showed significant worsening of cognitive function, fatigue, pain or depression during the 10-year follow-up. Conclusions: Currently accepted criteria for BMS diagnosis may cause overestimation of true prevalence, underscoring the need for routine monitoring of non-motor symptoms and imaging studies, to help physicians improve diagnostic accuracy as well as therapeutic decision-making in this subgroup of MS patients.