The Basophilic Fringe: A Case Report of Intestinal Spirochetosis in a Patient With Chronic Diarrhea

Intestinal spirochetosis is a rare infection of the colonic mucosa that often presents with nonspecific gastrointestinal symptoms despite largely normal endoscopic findings. Diagnosis depends on characteristic histologic features supported by immunohistochemical staining. Here, we present the case of a 57-year-old man with HIV, chronic abdominal pain, bloating, and long-standing watery diarrhea. His colonoscopy was largely unremarkable except for rectal ulcers. Histological examination of random colonic biopsies revealed a basophilic, brush-like fringe along the epithelial surface consistent with intestinal spirochetosis, which demonstrated immunoreactivity with anti-Treponema pallidum staining. Treatment with metronidazole led to the complete resolution of symptoms. This case underscores the importance of considering intestinal spirochetosis in patients with chronic diarrhea and abdominal pain when endoscopic findings are nonspecific, as prompt histologic diagnosis allows for effective treatment.