Colonic Diffuse Large B-cell Lymphoma Hidden in Actinomycosis.

Actinomycosis can mask malignant diseases. This paper reports a case of colonic diffuse large B-cell lymphoma (DLBCL), which was misdiagnosed as abdominal actinomycosis. A 76-year-old woman presented with right flank pain and weight loss. Abdominal CT and colonoscopy revealed a huge ascending colon mass. Despite the initial impression of a malignancy, a colonoscopic biopsy revealed no malignant cells, but sulfur granules and a filamentous organism suggesting actinomycosis. Intravenous penicillin G was administered under the impression of abdominal actinomycosis but her condition deteriorated rapidly. Follow up CT showed markedly increased colon mass and new multiple nodular lesions around the ascending colon. Sono-guided percutaneous biopsy of the nodular lesion was performed. The pathological result was DLBCL. The patient was scheduled to undergo chemotherapy but the patient expired due to cancer progression. The diagnosis of gastrointestinal infiltrating tumors is often difficult because a superficial biopsy usually does not provide a confirmative diagnosis. This case highlights the difficulty in making a correct diagnosis of lymphoma due to the concomitant actinomycosis. Malignant conditions must be considered in cases of actinomycosis with no response to antimicrobial therapy.