Atypical hidradenitis suppurativa.

Hidradenitis suppurativa (HS) is a chronic relapsing inflammatory disease resulting in subcutaneous abscesses, sinus tracts and scarring, arising predominantly in apocrine gland-bearing skin. The sites affected, in order of frequency, are the axillae, groins, perianal and perineal region, mammary and submammary skin, buttocks, and pubic region. Other sites that may be affected more rarely include the chest, eyelids, scalp, retroauricular and preauricular skin, thighs, and abdomen. Research has suggested that mechanical friction and follicular occlusion is the primary cause of HS. HS is one of the conditions of the 'follicular occlusion tetrad', which share a similar pathogenesis. HS at atypical sites may mimic other conditions both clinically and pathologically, so misdiagnosis is possible. We present a case series that illustrates a range of atypical sites affected. Our patients all had severe disease. Satisfactory control has not been achieved despite years of medical and surgical interventions.