Psoriasis and the risk of incident diabetes mellitus : a population-based study

BACKGROUND: Cross-sectional studies, mostly in hospitalized patients, reported a possible positive association between psoriasis and diabetes mellitus (DM). However, information on the temporal relation is scarce, and incidence rates of new-onset DM in patients with psoriasis are lacking. OBJECTIVES: To assess and compare incidence rates of new-onset DM between patients with psoriasis and a comparison group without psoriasis, and to explore the role of psoriasis severity and body mass index (BMI). METHODS: We conducted a follow-up study with a nested case-control analysis within the U.K.-based General Practice Research Database. The study population consisted of patients with a first-time diagnosis of psoriasis between 1994 and 2005 and a matched group of psoriasis-free patients. We used psoriasis duration and treatment as proxy for disease severity, and we applied conditional logistic regression to obtain odds ratios (ORs) with 95% confidence intervals (CIs). RESULTS: Within the study population of 65 449 patients we identified 1061 incident cases of DM. Of these, 59% had a history of psoriasis, yielding a crude incidence rate ratio of 1.36 (95% CI 1.20-1.53). The adjusted OR for patients with <or=2 years disease duration and <2 prescriptions per year for oral psoriasis treatment was 2.56 (95% CI 1.11-5.92). In an analysis restricted to patients with normal BMI, the adjusted OR was 2.02 (95% CI 1.31-3.10). CONCLUSIONS: In this large observational study the risk of incident DM was increased for patients with psoriasis as compared with a psoriasis-free comparison group. The risk increased with psoriasis duration and severity and was not driven by high BMI alone.