A baby with a raised brown lesion on the leg

Case presentation

A 9-month-old girl presents with a single plaque (3 x 1 cm) located over the posterior aspect of the knee (Figure). The lesion, which is raised and light brown in colour, first appeared when she was 3 months of age. At first the lesion blistered recurrently, and it was treated with topical mupirocin several times. The blistering stopped after three months, but the lesion has persisted. Her parents have noted that from time to time the lesion swells and becomes erythematous, returning to normal over about 20 minutes.