Incident Comorbid Diabetes and Outcomes in Multiple Sclerosis: An English Population‐Based Cohort Study

ABSTRACT Objective To compare the incidence of diabetes mellitus and its associations with hospitalisation and mortality in adults with multiple sclerosis (MS) and matched controls. Methods Using English primary care data from the Clinical Practice Research Datalink, linked to hospital and mortality records, we matched adults with MS with up to 10 controls without MS by age, sex and practice. We excluded individuals with pre‐existing diabetes mellitus. Outcomes included all‐cause hospitalisation (number and duration) and mortality. We used Poisson, negative binomial, linear and Cox proportional hazards models, adjusting for demographic and socioeconomic factors, with interaction terms for ethnicity, deprivation and urbanity. Results We included 47,247 individuals with MS and 458,951 matched controls. Over a mean follow‐up of 15.2 years, people with MS had a higher incidence of diabetes mellitus (adjusted incidence rate ratio = 1.16, 95% confidence interval 1.11–1.21). Among people with MS, incident diabetes mellitus was associated with higher hospitalisation rates (adjusted incidence rate ratio = 1.52, 1.42–1.64), longer hospitalisation duration (median 12 vs. 2 days) and increased mortality (adjusted hazard ratio = 1.41, 1.31–1.49). Similar patterns were observed among controls. The association between diabetes mellitus and increased hospitalisation was stronger in rural areas among those with MS and in White groups among controls. Interpretation MS was associated with a higher incidence of diabetes mellitus, which was in turn associated with greater hospitalisation and mortality. These findings may support consideration of equitable screening, prevention and management of diabetes mellitus in people living with MS.