Supplementary Material for: Hospitalisations with Hidradenitis Suppurativa: An Increasing Problem That Deserves Closer Attention

<p><b><i>Background/Aims:</i></b> Hidradenitis suppurativa (HS), a chronic inflammatory skin disease of the hair follicle, can lead to scarring and disability. With an estimated European prevalence of 1%, few epidemiological studies of HS have been performed, and none focused on hospitalisations. We aimed to study the time trends of HS hospitalisations and to evaluate the demographic characteristics, hospital incidence rate, readmissions, length of stay, comorbidities and risk factors of hospitalised HS patients. <b><i>Methods:</i></b> We performed a retrospective observational study using a national administrative database in Portugal, with discharges between 2000 and 2014. All the inpatients aged 5 years or more with a diagnosis of HS were included. Variables analysed were age, sex, admission and discharge date, discharge outcome and diagnoses. <b><i>Results:</i></b> A total of 1,177 patients were hospitalised in this time period (48 were aged 18 years or younger) with a male-to-female ratio of 1:1.17. There was a hospital incidence rate of 0.83 patients with HS per 100,000 person-years (95% CI = 0.78-0.88). The age group with the highest incidence rate was 20-29 years among women and 40-49 years among men. We recorded an increasing trend in the number of new hospitalised patients and in the hospital incidence rate of HS. Tobacco was the most common comorbidity/risk factor. Eighty-three percent of our population underwent HS surgery. <b><i>Conclusion:</i></b> This hospital-based incidence study showed that admission for HS is increasing and that the majority of the HS inpatients were surgical cases. In the future, prospective studies will be important to assess risk factors for hospitalisations and complications.</p>