Cactus granuloma of the skin.

A case of cactus granuloma due to the thorns of Opuntia bieglovii Engelman is reported. A 24-year-old Japanese man contacted the thorns of this cactus in Palm Springs, California, U.S.A., and, three months later, numerous, slightly elevated papules 2 to 4 mm in diameter appeared on the dorsum of his right hand and fingers. Histopathological examination revealed many small granulomas surrounding the bristle fragments throughout the dermis. The granulomas consisted of epithelioid cells, Langhans type and foreign body type giant cells. The fragments of the barbed bristles gave strongly positive reactions with PAS. Two hypothetical mechanisms, one allergic and the other non-allergic, are offered to explain this granuloma formation and are discussed with reference to the literature.