Psoriatic onycho-pachydermo-periostitis progressing to generalized pustular psoriasis

Conflict of interest: none declared. Psoriatic onycho‐pachydermo‐periostitis (POPP), first described in 1989, is a rare subtype of psoriatic arthritis characterized by onychodystrophy, connective tissue thickening above the distal phalanx, and periosteal reaction.1 We report the first case of POPP progressing to generalized pustular psoriasis (GPP). A 59‐year‐old man presented with a 3‐month history of nail changes and painful swelling of the toes. He also had a 1‐week history of high fever and diffuse erythema over his whole body. On physical examination, prominent swelling of all fingers and toes was seen, which was associated with pain in the distal interphalangeal (DIP) joints (Figs 1a,b). Severe onycholysis and subungal debris was seen in all finger and toe nails. There were multiple scaly erythematous plaques with pustules over the whole of the patient’s body (Fig. 1c). Mycological examinations of the nails gave negative results. On histological examination of a skin biopsy from an erythematous plaque on the right lower leg, we found parakeratosis, regular acanthosis and subcorneal pustules consisting of neutrophils (Fig. 1d). Similar histopathological findings were seen in biopsies of the nail.