Abstract

Actinomycosis is a rare, chronic granulomatous disease caused by filamentous, anaerobic, gram-positive bacteria that typically colonize the human mouth. Infection classically occurs in the cervicofacial area, the abdomen, or the thorax. Pelvic actinomycosis rarely occurs, usually associated with intrauterine devices. We report a 30-year-old-man with no significant past medical or surgical history who presented to the emergency room with a 2-week history of perianal pain and firmness. Examination of the area revealed an indurated, non-fluctuant, erythematous mass located 2cm from the anus. The patient was treated with trimethoprim-sulfamethoxazole and topical mupirocin for presumed cellulitis. Five days later the mass had doubled in size. The patient was switched to clindamycin and referred for surgical excision. The excision specimen revealed a dense infiltrate of lymphocytes, neutrophils, plasma cells, eosinophils, and histiocytes partially filling the reticular dermis and extending into the subcutaneous fat. The infiltrate surrounded grains of basophilic material with an outer rim of eosinophilic radiating Splendore-Hoeppli material. Within the grains, filamentous bacteria were highlighted with PAS and GMS, gram-positive with Brown-Brenn and Brown-Hopps, and negative with acid fast stains. A few filamentous bacteria were present in the infiltrate outside of the grains. Given the clinical and histologic findings, actinomycosis was diagnosed. Two weeks later the patient reported resolution of symptoms. Evaluation and treatment is ongoing. This case highlights an unusual presentation of actinomycosis and how histology facilitates the diagnosis of this unusual pathogen. The views expressed in this abstract are those of the author(s) and do not necessarily reflect the official policy of the Department of Defense or the U.S. Government.

Financial Disclosure:
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