Abstract

Peristomal amebiasis is rarely described, with only 3 cases reported since 1973. We present a 45yo man with metastatic rectal cancer status-post resection and colostomy. While undergoing chemotherapy, he developed a 2cm ulcer with undermined borders below his stoma. Skin biopsy revealed acute and chronic inflammation with abscess formation. Despite initial treatment with antibiotics, the ulcer rapidly expanded to 13 x 7cm. Repeat biopsy demonstrated pan-dermal mixed inflammation including neutrophils. Brown and Brenn, GMS, and AFB stains were negative for microorganisms, and the working diagnosis was pyoderma gangrenosum. The patient was treated with prednisone, cyclosporine, and infliximab without significant improvement. He subsequently developed hematochezia. Endoscopy revealed extensive esophageal and colonic ulceration. Stool PCR studies returned positive for Entamoeba histolytica. Re-review of prior ulcer biopsies with PAS staining highlighted large, oval, unicellular structures within the dermis consistent with trophozoites. Immunosuppression was stopped and the patient was treated with metronidazole, paromomycin and a split-thickness skin graft with complete healing. Cutaneous amebiasis remains a health issue in developing countries as a cause of painful ulcers, often in the perineal area. Amoebae destroy tissue rapidly but are easily treated with antimicrobials. Peristomal amebiasis is not widely recognized and may be underdiagnosed in peristomal ulcers. We recommend clinicians and pathologists consider cutaneous amebiasis in the differential diagnosis for ulceration unresponsive to therapy, particularly in the setting of plausible skin contamination with stool. Amoebae are more readily detected with PAS staining compared to GMS, and clinicians should consider PCR studies as well as PAS in recalcitrant cases.