Perianal streptococcal infection precipitating pustular psoriasis in an adult

Fig 1. Well-demarcated salmon-pink to erythematous plaque with overlying scale and pustules on the right side of the groin. CASE REPORT A68-year-oldmanwhowasotherwisewell,with no personal or family history of skin disease and not on any regular medications, developed a perianal/groin irritation after a digital prostate examination. His general practitioner diagnosed seborrheic dermatitis with secondary fungal infection and treated him empirically with topical betamethasone valerate cream, clotrimazole cream, and oral cephalexin. A swabdemonstrated Streptococcus pyogenes. The eruption progressed into widespread erythematous symmetric papules and plaques and he was referred to a dermatologist, who made an assessment of contact dermatitis with id reaction (potentially to the KY jelly [Reckitt Benckiser, Slough, UK] or latex gloves used in the examination) and secondary infection in the groin. Oral prednisolone was commenced at 50 mg, tapered to 25 mg, as was topical methylprednisolone aceponate. After this, the eruption became pustular and the patient was admitted under dermatology in a tertiary hospital. On admission, the patient had a low-grade fever but was otherwise hemodynamically stable and systemically well with an increased C-reactive protein level of 43 mg/L (normal\8.0 mg/L) and mildly increased white blood cell count of 12.8 3 10/L (normal 4e11 3 10/L) with associated neutrophilia at 11.66 3 10/L (normal 1.8-7.5 3 10/L) and