Hidradenitis suppurativa (HS): An unrecognized paradoxical effect of biologic agents (BA) used in chronic inflammatory diseases

Background: Paradoxical hidradenitis suppurativa (HS) induced by biologic agents (BA) is scarcely reported. Objective: We sought to describe the clinical characteristics and outcome of patients developing paradoxical HS under BA. Methods: This was a multicenter nationwide retrospective study asking physicians to report all cases of HS, confirmed by a dermatologist, occurring during treatment of an inflammatory disease by a BA. Results: We included 25 patients (15 inflammatory rheumatism, 9 Crohn's disease, 1 psoriasis) treated by 5 BA (adalimumab = 12, infliximab = 6, etanercept = 4, rituximab= 2, tocilizumab = 1). Median duration of BA exposure before HS onset was 12 (range 1-120) months. Patients were mostly Hurley stage I (n = 13) or II (n = 11). Simultaneously to HS or within 1 year, 11 patients developed additional inflammatory diseases, including paradoxical reactions (psoriasis = 9, Crohn's disease = 3, alopecia areata = 1, erythema elevatum diutinum = 1). Complete improvement of HS was more frequently obtained after BA discontinuation or switch (n = 6/10, 60%) rather than maintenance (n = 1/14, 7%). Reintroducing the same BA resulted in HS relapse in 3 of 3 patients. Limitations: Retrospective nature and lack of complete follow-up for some patients are limitations. Conclusion: HS is a rare paradoxical adverse effect of BA, but fortuitous association cannot be excluded in some cases. We observed a trend toward better outcome when the BA was discontinued or switched.