Population-based Clinical Practice Research Datalink study using algorithm modelling to identify the true burden of hidradenitis suppurativa

BACKGROUND: Epidemiology data regarding hidradenitis suppurativa (HS) are conflicting and prevalence estimates vary 80-fold, from 0·05% in a population-based study to 4%. OBJECTIVES: To assess the hypothesis that previous population-based studies underestimated true HS prevalence by missing undiagnosed cases. METHODS: We performed a population-based observational and case-control study using the U.K. Clinical Practice Research Datalink (CPRD) linked to hospital episode statistics data. Physician-diagnosed cases in the CPRD were identified from specific Read codes. Algorithms identified unrecognized 'proxy' cases, with at least five Read code records for boils in flexural skin sites. Validation of proxy cases was undertaken with general practitioner (GP) questionnaires to confirm criteria-diagnosed cases. A case-control study assessed disease associations. RESULTS: ) were 3·61 (95% CI 3·44-3·79) and 3·29 (95% CI 3·14-3·45). HS was associated with type 2 diabetes, Crohn disease, hyperlipidaemia, acne and depression, and not associated with ulcerative colitis or polycystic ovary syndrome. CONCLUSIONS: Contrary to results of previous population-based studies, HS is relatively common, with a U.K. prevalence of 0·77%, one-third being unrecognized, criteria-diagnosed cases using the most stringent disease definition. If individuals with probable cases are included, HS prevalence rises to 1·19%.