To report a rare case of diffuse intestinal schistosomiasis involving the entire colon, mimicking ulcerative colitis, and to emphasize the importance of considering parasitic infections in the differential diagnosis of pancolitis in endemic regions.

A 31-year-old male from Consolacion, Cebu, presented with painless hematochezia and was initially admitted for planned hemorrhoidectomy. Due to persistent bleeding, colonoscopy was performed, which revealed continuous mucosal ulceration and inflammation from the rectum to the cecum. An initial endoscopic impression of ulcerative colitis was made. Systematic biopsies were obtained from all colonic segments, and stool microscopy for ova and parasites was performed.

Stool microscopy was negative for parasitic ova. However, histopathological examination of colonic biopsies demonstrated numerous Schistosoma ova embedded within the lamina propria throughout all sampled segments, confirming extensive intestinal schistosomiasis. The patient was treated with praziquantel and subsequently underwent hemorrhoidectomy. Complete resolution of hematochezia was observed, with no recurrence on follow-up. This case illustrates the significant diagnostic challenge posed by diffuse egg deposition producing a pancolitis pattern that closely mimics inflammatory bowel disease.

Pan-colonic involvement in intestinal schistosomiasis is exceedingly rare, as the disease typically localizes to the rectum and sigmoid colon. In endemic regions, schistosomiasis should be strongly considered in cases of diffuse colitis, even when stool examinations are negative. Mucosal biopsy remains the diagnostic gold standard. Early recognition allows effective treatment with praziquantel and prevents misdiagnosis and unnecessary long-term immunosuppressive therapy.