Disseminated molluscum contagiosum in a patient with chronic plaque psoriasis taking methotrexate

Abstract

Conflict of interest: none declared. A 69‐year‐old man with a 3‐year history of chronic plaque psoriasis presented with an itchy papular eruption over the trunk, progressing to involve the buttocks and limbs over a period of 3 months. He had been on oral methotrexate 7.5 mg/week for the previous 2 years (cumulative dose 1110 mg) for his psoriasis, and had not received phototherapy. He was otherwise well with no history of recurrent infections or recent ill health. Physical examination revealed smooth discrete yellowish papules, 2–5 mm in diameter, over the back, buttocks and limbs (Figs 1 and 2). Psoriasiform plaques were observed over the scalp. The rest of the examination was normal. Differential diagnoses considered were disseminated molluscum contagiosum, xanthogranulomas or eruptive xanthoma. Punch biopsy of a papule from the right thigh revealed a focal endophytic growth consisting of hyperplastic keratinocytes containing eosinophilic intracytoplasmic inclusions (Fig. 3). Laboratory findings revealed an unremarkable white cell count (5.4 × 109/L; normal range 4–10 × 109/L) with a normal differential count. The rest of the full blood count, and the renal and liver function tests were normal. An antibody assay for human immunodeficiency virus (HIV) was negative. A diagnosis of disseminated molluscum contagiosum was made and methotrexate was stopped. This resulted in a clear regression of the molluscum lesions within 3 months, although some papules still persisted. Cryotherapy for the residual lesions resulted in complete clearance. Fair control of his psoriasis was maintained with topical therapy with no further relapse of the molluscum contagiosum.