Concomitant autoimmunity and risk of multiple sclerosis disability worsening

Background: Few studies have examined the effect of concomitant autoimmune diseases on multiple sclerosis (MS) disability worsening. We set out to examine whether concomitant Crohn's Disease (CD), Ulcerative Colitis (UC), or Type 1 Diabetes (T1D) affect MS disability worsening in a nationwide cohort of MS patients as defined by reaching expanded disability scale status (EDSS) scores 3.0, 4.0 and 6.0. Methods: Patients with MS onset between January 2004 and January 2019 were identified from the Swedish MS registry and the Swedish National Patient Register. Kaplan–Meier analysis was used to estimate the median time to reach sustained disability milestones. Adjusted Cox proportional hazard regression models were used to calculate the risk of reaching disability milestones among persons with and without CD, UC, or T1D. Results: Out of 8972 persons with MS, 88 (1.0 %) had T1D, 47 (0.8 %) had UC, and 78 (0.9 %) had CD. There was a significantly higher risk of disability progression, for persons with MS and T1D for reaching EDSS 6.0, hazard ratio (HR) = 2.21 (95 % confidence interval (CI) = 1.48 −3.31) and persons with MS and comorbid CD for reaching EDSS 3.0, HR = 2.30 (95 %CI = 1.74–3.04) and 4.0, HR = 1.59 (95 %CI = 1.09–2.32), and persons with MS and comorbid UC for reaching EDSS 3.0 HR = 1.57 (95 %CI = 1.15–2.14). As defined by Charlson's comorbidity index, the co-existence of other co-morbidities conferred a significant increase in the risk of reaching all endpoints, with HR ranging from 1.23 to 1.62. Conclusion: Comorbidity is associated with a significantly increased risk of reaching disability end-points, and T1D, CD, and UC increase the risk further. Thus, there appears to be a need for increased vigilance of comorbidites in persons with MS in order to optimise the long-term outcome of MS.