Sub-classification of Hidradenitis suppurativa: a cross-sectional study.

The typical Hidradenitis Suppurativa (HS) patient is a young woman with axillary and groin involvement, but the spectrum of the disease presentation is broad and no internationally acknowledged sub-classification of the disease exists to date. It is however speculated that different, yet unidentified, subtypes may respond differently to different treatments or carry a different prognosis. Classification according to self-reported clinically meaningful outcomes for patients offer practical advantages. Our objective was to build an empirical framework for sub-classification of HS patients based on the frequency of HS flares in various anatomic locations, using a cross-sectional questionnaire-based design. All patients with a clinically confirmed diagnosis of HS registered at our department until March 1, 2017 were invited to participate. The frequency of HS flares in various anatomic locations was used for identification of possible HS subtypes using Principal Component Analysis (PCA) and cluster analysis. A total of 524 (62%) of 845 invited patients answered the questionnaire; 402 (76.7%) were female. From the cluster analysis, we identified two possible subtypes of HS, labeled the "upper type" and the "lower type". The "upper type" was characterized by repeated outbreaks in axillary and mammary regions. Meanwhile, the "lower type" was characterized by outbreaks in the inguinal, genital, perianal, and gluteal regions. Our findings support the notion that HS can be sub-classified and imply that the pattern of where lesions are located may be an important element in future HS sub-classification systems.