Ameboma

Abstract

61 Hispanic male with a history of hypercholestorolemia was referred to our clinic for a screening colonoscopy. He denied any complaints of weight loss, diarrhea, abdominal pain, hematochezia, melena fever, chills or fatigue. He was originally from South America, but had been in the U.S. for over five years. Our patient had no abnormal labaratory findings. On colonoscopy he was found to have a 2 cm ulcerated, friable flat mass with exudate in the ascending colon just outside the cecum. Histology revealed an ameboma which was described as severe active chronic inflammation with an exudate fragment showing trophozoites with erythrophagocytosis. The patient was treated with 10 days of metronidazole followed by 10 days of paromomycin. Intestinal amebiasis is caused by the protozoan Entamoeba Hystolytica. Worldwide 30–50 million symptomatic infections occur. It is the third most common parasitic cause of death. In the United states most of the cases are seen in immigrants from developing countries and travelers. Infection begins with ingestion of cysts from fecally contaminated water or food. Excystation occurs in the small bowel where trophozoites emerge. Ninety percent of patients colonized by E. Hystolytica spontaneously clear the infection by one year. Most patients are asymptomatic, however invasive intestinal amebiasis may mimic inflammatory bowel disease, malignancy and malsbsorptive illnesses. Extraintestinal manifestations are uncommon. They include liver abscesses, pleuropulmonary disease, cerebritis and pericarditis. Diagnosis is made by serologic and stool examinations.Microscopic examination of the stool has a low sensitivity 30–60%. A high false positive rate exists secondary to non pathogenic entamoebas which are morphologically identical to and more common then entamoeba hystolytica.ELISA stool antigen test which detects adherence lectin antigen has a sensitivity of 87% and a specificity of greater than than 90%. Seum antibody tests are most useful for extraintestinal disease when organisms are not found in the stool. Antibodies are detectable by the first week of infection and may persist for years. Up to 25% of uninfected patients in endemic regions are positive. An Ameboma is an unususual manifestation of entamoeba hystolytica. In immigrants from developing countries with atypical colonic masses one must consider entamoeba hystolytica as part of their differential diagnosis.