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‘Clinically definite benign multiple sclerosis’, an unwarranted conceptual hodgepodge: evidence from a 30-year observational study

Background: Benign multiple sclerosis (BMS) is a controversial concept which is still debated. However identification of this kind of patients is crucial to prevent them from unnecessary exposure to aggressive and/or long term medical treatments. Objectives: To assess two definitions of ‘clinically definite benign multiple sclerosis’ (CDBMS) using long-term follow-up data, and to look for prognostic factors of CDBMS. Methods: In 874 patients with definite relapsing–remitting MS, followed up for at least 10 years, disability was assessed using the Disability Status Scale (DSS). CDBMS was defined by either DSS score≤2 (CDBMS1 group) or DSS score≤ 3 (CDBMS2 group) at 10 years. We estimated the proportion of patients who were still benign at 20 and 30 years after clinical onset. Results: CDBMS frequency estimates were 57.7% and 73.9% when using CDBMS1 and CDBMS2 definitions, respectively. In the CDBMS1 group, only 41.7% (105/252) of cases were still benign 10 years later, and 41.1% (23/56) after an additional decade, while there were 53.8% (162/301) and 59.5% (44/74) respectively in the CDBMS2 group. Conclusions: This 30-year observational study, which is one of the largest published series, indicates that favourable 10-year disability scores of DSS 2 or 3 fail to ensure a long-term benign course of multiple sclerosis. After every decade almost half of the CDBMS were no longer benign. CDBMS, as currently defined, is an unwarranted conceptual hodgepodge. Other criteria using new biomarkers (genetic, biologic or MRI) should be found to detect benign cases of MS.