Abstract
A 60-year-old Japanese man presented with bloody diarrhoea. He stated that he had been diagnosed with ulcerative colitis (UC) 3 years prior, but discontinued follow-up care as treatment was ineffective. One year later, he came to our hospital with anorexia and weight loss. The abdomen was soft and flat without tenderness. Laboratory tests were unremarkable; faecal culture and Clostridium difficile toxin were negative. Findings and biopsy from a subsequent colonoscopy reconfirmed his diagnosis of UC. Neither mesalazine, which was initially prescribed, nor additional treatments improved his symptoms. Repeat colonoscopy, performed 5 months later, demonstrated similar findings in the same area. Although the pathology remained consistent with UC, multiple treatment failures suggested ongoing occult infection. Additional testing revealed positive Entamoeba histolytica antibody. 14 days of metronidazole dramatically improved his symptoms. He has remained asymptomatic after 2 years.