Hydroxyapatite pseudopodagra in a young man: acute calcific periarthritis of the first metatarsophalangeal joint.

Pain and swelling at the first metatarsophalangeal joint can be caused by acute calcific periarthritis (ACP), an inflammatory condition resulting from deposition of hydroxyapatite crystals. A case is reported of a 23-year-old man in whom ACP was initially mistaken for gout, septic arthritis, and cellulitis. The diagnosis of ACP is based on the finding of inflammation around a joint along with radiographic evidence of periarticular soft tissue calcifications. Calcifications may disappear over time, as they did in this case. Failure to recognize this condition can lead to unnecessary testing and inappropriate treatment.