Pyoderma gangrenosum and suppurative hidradenitis association, overlap or spectrum of the same disease? Case report and discussion

Suppurative hidradenitis and pyoderma gangrenosum are rare disorders that can be seen isolated or even more rare, as part of different autoinflammatory syndromes: Pyoderma gangrenosum, acne, and hidradenitis suppurativa (PASH), pyoderma gangrenosum, acne, pyogenic arthritis, and hidradenitis suppurativa (PAPASH) or psoriatic arthritis, pyoderma gangrenosum, acne, and hidradenitis suppurativa (PsAPASH). Although they have different clinical features, suppurative hidradenitis and pyoderma gangrenosum seem to share similar pathogenic pathways involving a dysregulated innate immune system, with neutrophilic inflammation, mediated by IL-1β, controlled by NALP3 inflammasome pathway. We report a case of a 53-year-old male patient previously diagnosed with HS in inguinal-scrotal area that developed rapidly after a traumatic injury on his left anterior calf, a painful inflammatory plaque with pustules on the surface that rapidly progressed (24-48 h) to form ulcers. The lesions ended up healing with a large scarring plaque with cribriform openings, multiple fibrous bridges, open comedones, and double-ended pseudo-comedones. Although the clinical aspect at presentation together with the aspect on the first biopsy were suggestive for pyoderma gangrenosum, the healing aspect is more commonly seen in suppurative hidradenitis. Commonly seen in acne, in the healing phase of suppurative hidradenitis but more rarely in pyoderma gangrenosum, the formation of comedones seem to be a complex process and raise the question if these entities represent in our patient an association, an overlap or the spectrum of the same disease.