Background
In 40% of all cases of Crohn's disease fistulas emerge during the course of disease. Nevertheless, acne inversa has to be taken into account as an infrequent differential diagnosis. Infliximab as an antibody against the pro-inflammatory mediator TNF-alpha is active in cases of acute Crohn's disease, concomitant fistulas and cutaneous manifestations.
Material and Method
We report on the case of a 54-year-old patient suffering for five years from a severe suppurative fistuling cutaneous disease concomitant to Crohn's disease. At the start of treatment the histological findings of a specimen presented chronically fibrosing lymphoplasmacellular dermatitis with both a very high number of plasma cells and a burrow-like fistula system. Due to superinfection the treatment was at first based on the administration of intravenous and oral doses of antibiotic agents, followed by a treatment course of 14 months with methotrexate and seven applications of infliximab. During the Crohn's disease, which was accompanied by persisting concomitant discomforts, an extensive surgical sanitation of the fistulous tracts was performed. Acne inversa was diagnosed in the subsequent histological analysis of the operative specimen.
Results

Conclusions
Acne inversa is a very rare cutaneous disease. Several case reports describe the successful treatment of acne inversa concomitant to Crohn's disease using anti-TNF-alpha-antibodies. The long-term course of the case presented here shows that the non-response to infliximab might be caused by both the long duration and the distinct grade of seriousness of the acne inversa.

Keywords: Methotrexate - therapeutic use, Hidradenitis Suppurativa - pathology, Crohn Disease - complications, Antibodies, Monoclonal - therapeutic use