A 55-year-old man presented to a clinic with a one-month history of constipation and mucous and bloody stools. He was diagnosed as having rectal cancer at the clinic and referred to our hospital for treatment. We performed colonoscopy to reevaluate the cancer. In addition to the cancer, an irregular ulcerated lesion covered with a white exudate was observed at the anal aspect of the cancer in the rectum. A biopsy specimen was taken from the ulcerated lesion, and microscopic examination revealed trophozoites of Entamoeba histolytica. We diagnosed the patient as a case of rectal cancer associated with amoebic colitis.
Routine clinical tests such as complete blood count, serologic tests for syphilis, HIV, HBV, HCV, liver function tests, and renal function tests revealed no abnormalities. The serum titer for antibody against E. histolytica was 100-fold and the serum CEA level was 5.3 ng/ml. The patient was treated for amoebic colitis preoperatively with paromomycin (1,500 mg/day) for 10 days. Colonoscopy revealed complete healing of the mucosal lesion distal to the tumor after the antibiotic therapy, and a laparoscopic low anterior resection was performed for the rectal cancer.
The patient’s postoperative course was uneventful, and he was discharged on postoperative day 8. We report this rare case and the benefits of preoperative antibiotic therapy for such cases.