Actinomycosis of the accessory breast treated with cotrimoxazole.

Actinomycosis is a chronic suppurative granulomatous disease caused by the filamentous bacteria, Actinomyces israelii, which was once thought to be a fungus. It is a Gram-positive, aerobic or microaerophillic, non acid-fast hyphal organism which fragments into coccoid or bacillary forms and, unlike the fungus, does not form conidia. Accessory breast tissue usually occurs along the milk lines, frequently in the axilla and rarely in the thighs. Actinomycosis of the breast is very uncommon and we report the case of a multiparous woman who had a painful lump in the axilla which, on histopathologic examination, showed actinomycosis within the accessory breast tissue.