An annular plaque on the hand

A 41 year old man presented with a five month history of a painless, non-pruritic rash on his left hand (fig 1). Six months earlier he had received cryotherapy with liquid nitrogen—applied using a cotton wool bud—for a common wart in the same location. The day after cryotherapy, a painful, haemorrhagic blister occurred at the treatment site. The blister was drained, and over the next 20 days it dried and healed. Two weeks later a new lesion developed on the rim of …