Is benign MS really benign? What a meaningful classification beyond the EDSS must take into consideration.

BACKGROUND

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease with an unpredictable course that has a broad clinical spectrum and progresses over time. If a person with MS (PwMS) shows overall mild to moderate disability even after a long duration of disease, the term benign MS (BMS) is used. However, there is currently no generally accepted definition of BMS. Most definitions are based on EDSS in connection with disease duration, i.e. EDSS ≤3.0 after 15 years' disease duration. The question arises whether focusing on EDSS alone is adequate for classifying the disease course taking into account that 'hidden' or 'soft' symptoms are not sufficiently covered by this instrument. The aims of the study are to assess the prevalence of BMS in one of the largest patient cohorts, to describe the prevalence of patients without disabilities and to assess the further disability progression of these patients over another 15 years.

METHODS

Based on data exported from the German MS Registry, PwMS with a disease duration of 15 years or more were included in the analyses. PwMS were divided into BMS (EDSS ≤3.0) or non-benign (NBMS, EDSS >3.0).

RESULTS

Out of 31,824 PwMS included in the German MS Register, we identified 10,874 patients with a disease duration ≥15 years of whom 4,511 (42%) showed an EDSS ≤3.0 fulfilling the criterion of benign MS. In the subgroup with EDSS measured exactly at 15 years' disease duration, the proportion was 54%. This proportion decreased continuously with increasing disease duration and fell to 30% after 30 years. Female sex (hazard ratio [HR]: 0.84) was associated with BMS, while a progressive (HR: 2.09) and late disease onset (HR: 1.29) were associated with NBMS (p<0.001). With a more rigorous definition of BMS (EDSS ≤1.0, absence of disability, and active employment), only 580 (13%) of the initial BMS remained 'benign'.

CONCLUSION

Our data propose an alternative definition (EDSS ≤1.0, absence from any disability, and the ability to work after 15 years of disease duration) which might truly reflect BMS.