Incidence and remission rates of self-reported hidradenitis suppurativa - A prospective cohort study conducted in Danish blood donors

Background A large discrepancy between physician-diagnosed and self-reported Hidradenitis suppurativa (HS) exists. Knowledge regarding incidence and remission rates of self-reported HS is missing, but may help bridge the gap in understanding between these two phenotypes. Objectives To determine the incidence and remission rates of self-reported HS, and to what degree these are affected by sex, smoking and BMI. Methods A prospective cohort of 23 930 Danish blood donors. Information on self-reported HS, symptom-localisation, sex, age, BMI and smoking status was collected at baseline and study termination. Self-reported HS fulfilled clinical obligatory diagnostic criteria. Cox proportional hazards regression analyses were conducted for both incidence and remission rates providing a hazard ratio (HR) of risk for each variable in the regression. Results Incidence rate of self-reported HS was 10.8/1000 person-years (95% confidence interval (CI): 9.9–11.7), decreasing as a function of numbers of areas affected. Female BMI points above 25 (HR = 1.11, 95% CI: 1.09–1.13), male BMI points above 25 (HR = 1.07, 95% CI: 1.04–1.11), active smoking (HR = 1.72, 95% CI: 1.15–2.57), male sex (HR = 0.55, 95% CI: 0.45–0.67) and years of age above 25 (HR = 0.97, 95% CI: 0.96–0.97) were all statistically associated with the development of self-reported HS. Remission rate of self-reported HS was 256.7/1000 person-years (95% CI: 223.9–292.6), decreasing as a function of numbers of affected areas. Symptoms in ≥3 areas (HR = 0.54, 95% CI: 0.34–0.85), active smoking (HR = 0.49, 95% CI: 0.32–0.76) and female weight loss (every percentage drop in BMI: HR = 1.07, 95% CI: 1.05–1.11) all significantly affected the remission rate. Conclusions Both incidence and remission rates of self-reported HS are high, indicating that many with self-reported HS are unlikely to be diagnosed, as they to a higher degree experience mild transient HS symptoms.