Background: To prospectively investigate the incidence and relative risks of multiple sclerosis (MS) in patients with type 2 diabetes (T2DM).

Materials and methods: Patients with T2DM (n = 614,623) and age- and sex-matched controls (n = 614,021) were followed from 2000 to 2008 to identify cases of newly diagnosed MS (ICD-9-CM: 340). The person-year approach with Poisson assumption was used to evaluate the incidence density. We estimated the covariate-adjusted hazard ratio (HR) of MS incidence in relation to T2DM diabetes using a multiple Cox proportional hazard regression model.

Results: Over 9 years of follow-up, 175 T2DM patients were newly diagnosed with MS, and 114 matched controls had the same first-ever diagnosis, representing a covariate-adjusted HR of 1.44 (95% confidence interval [CI], 1.08–1.94). The sex-specific adjusted HR for both men and women with T2DM was also elevated at 1.34 (95% CI, 0.81–2.23) and 1.51 (95% CI, 1.05–2.19), respectively. Women aged ≤50 years had the greatest risk of MS (HR 2.16; 95% CI, 1.02–4.59).

Conclusion: This study demonstrated a moderate but significant association of T2DM with MS incidence, and the association was not confounded by socio-demographic characteristics or certain MS-related comorbidities.