Hidradenitis suppurativa at the knees

Hidradenitis suppurativa is a poorly understood, destructive disease centered on pilosebaceous units and characterized by inflammatory nodules that progress to abscesses, sinus tracts, and scars. The typical patient is a young woman with involvement of the axillae, breasts, and groin. Presented is a 60-year-old man with poorly controlled diabetes, who initially developed pink-to-yellowish plaques with punched out ulcers on his knees that evolved to scars and draining sinus tracts. Draining sinus tracts were also noted under the left axilla. Histopathology revealed suppurative granulomatous inflammation centered on hair follicles as well as sinus tracts. Special stains for fungus and mycobacterial bacilli were negative. Cultures and PCR for mycobacterial tuberculosis were negative. The patient was diagnosed with hidradenitis suppurativa. A treatment trial of topical corticosteroids and antibiotics was given, but this regimen failed to improve his lesions. The patient was then started on adalimumab, which yielded marked improvement within three months. This case is reported because of the unusual clinical presentation and to highlight the spectrum of atypical hidradenitis suppurativa.