Severe perineal hidradenitis suppurativa (HS) and anal fistulas. An underrated association

Abstract Background Due to its multiple forms of debut hidradenitis suppurativa has classically been a diagnostic challenge as well in the differential diagnosis. Prevalence of perianal fistula in patients with hidradenitis suppurativa ranges form 6,6% to 67%. The aim of the study was to assess both conditions. Methods A retrospective chart review from 2000 to 2018 using the ICD-9-CM, coded with 705.83. for patients with hidradenitis suppurativa was conducted. Hurley’s three stage classification was applied. Diagnosis and relevant patient characteristics were assessed and the presence of associated perianal fistula. Endoa-nal ultrasound (EAU) was performed in 61% of the patients with perianal hidradenitis and perianal fistu-la, and magnetic resonance imaging (MRI) in 19%. Results Of 143 cases with hidradenitis, sixty two cases (43,4%) presented perianal (perineal/buttocks) location. Of them 93,5% were men. Twenty-one percent were associated with perianal fistulas being 6 of them complex ones associated with Hurley stage II and III. Treatment for the latter included: loose setons in 4 patients with Crohn’s disease and in 2 non Crohn’s disease with complex fistulas, 4 fistulotomies and 2 fistulectomies in low transphincteric fistulas and 1 with incision and drainage. Conclusion Perianal fistula should be treated according to associated diseases and type of fistula. Association of hidradenitis and perianal fistulas may be higher than expected and the relation of severe hidradenitis with complex perianal fistulas should be studied further. Endoanal ultrasound and MRI may be useful tools to assess HS with complex perianal fistulas, but the iconographic patterns of hidradenitis and Crohn’s disease should be kept in mind as both may be associated.