A Rare Mimic of Colon Cancer: Ameboma

Abstract

Purpose: To appreciate the diagnostic challenge posed by ameboma in a patient encumbered with multiple ailments as well as to gain a brief insight into its clinico-pathological features and treatment options. Results: A 76-year-old male from Minnesota, with history of non-small cell lung cancer and prostate cancer, presented with subacute intestinal obstruction and hematochezia. He had recently started prednisone for radiation pneumonitis. Computed tomography of the abdomen revealed circumferential colonic wall thickening and exophytic masses extending from the cecum to the proximal transverse colon. Colonoscopy revealed multiple, partially obstructing, necrotic luminal masses in the same distribution. The differential diagnoses included extensive colon cancer, metastatic cancer, lymphoma, tuberculosis, and Yersinia colitis. A biopsy done to ascertain colon cancer showed instead hemophagocytic Entamoeba histolytica in flask-shaped ulcers confirming the diagnosis of ameboma. High serum anti-E. histolytica antibody titers and trophozoites and cysts in the stool provided corroborative evidence. The clinical enigma was resolved when subsequent questioning revealed that he was a frequent traveler to Central America and China, the last visit being 5 years ago. Treatment with Metronidazole for 3 weeks followed by Paromomycin for a week culminated in clinical and colonoscopic resolution. Conclusion:E. histolytica, a leading cause of parasitic death in developing nations, represents a significant health hazard for international travelers. Intestinal amebiasis is typified by colonic ulcero-inflammatory lesions and manifests as a clinical spectrum ranging from asymptomatic infection, through colitis, ameboma and toxic megacolon. Ameboma, a rare presentation even in endemic countries, is characterized by an inflammatory colonic mass indistinguishable from colon cancer. Complications include bleeding, bowel obstruction and perforation. As exemplified here, immunosuppression may precipitate severe symptoms in asymptomatic carriers several years after the sentinel infection. Metronidazole is the cornerstone of therapy followed by a luminal amebicide such as Paromomycin or Diloxanide furoate to eradicate colonization. Colonic mass in the setting of immunosupression and a history of travel to developing countries, even in the remote past, should raise the possibility of ameboma. Prompt diagnosis and treatment is imperative to prevent complications and unnecessary surgery.