A Case of Colonic Spirochetosis: An Enigma Unravelled

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Introduction: Spirochaetaceae encompass a small group of gram-negative bacilli that cause infestation and infections in humans, mainly in the large intestine. In the US most cases of intestinal spirochetosis (IS) are caused by Brachyspira aalborgi. The previously reported cases of IS have been diagnosed in biopsies of left colon or with stool studies. Case Report: A 42 year-old male without significant past medical history presented with chronic abdominal pain and bloating for the past 23 years. He described the pain as diffuse and colicky, which worsened with food intake and was relieved after a bowel movement. He also had intermittent episodes of diarrhea and tenesmus. Physical examination revealed a BMI of 33 kg/m2 and his abdomen had no abnormal findings. He had previously visited several physicians with same complaints and previous serological work up for Celiac disease had been negative with no final established diagnosis and incomplete relief from symptomatic therapy. EGD and colonoscopy were subsequently performed, which were grossly unremarkable with normal-appearing mucosa throughout. Random biopsies were obtained from the stomach, duodenum and colon. Histopathology results from both the right and left colon biopsies showed intestinal spirochetosis, which was clearly evident on routine H&E stain as well as on PAS stain with diastase (Figures 1 & 2). Patient was prescribed 2 weeks of oral metronidazole.Figure 1Figure 2Discussion: The reported prevalence of IS varies between 2.5% to 16% and occurs more commonly among homosexual males and patients with low socioeconomic status. A significant number of patients are HIV positive, but there is no link between the degree of immunodeficiency and the severity of disease. The methods of transmission are suspected to be fecal-oral or sexual contact. It remains to be confirmed whether intestinal spirochetes are pathogenic or commensal organisms, as majority of cases are asymptomatic. On colonoscopy, the mucosa can appear normal, erythematous or edematous. The hallmark histological feature includes a 3-μm basophilic fringe on the intestinal mucosal epithelium. IS has been reported in all parts of the colon, including the appendix and rectum. We found these organisms on random biopsies of the colon, including the right side which has not been frequently reported. Metronidazole is the antibiotic of choice for treatment of symptomatic IS, other options include tetracycline, ceftriaxone and meropenem. For asymptomatic IS, watchful waiting is preferred.