Intestinal Spirochaetosis

Intestinal spirochaetosis is colonisation of the colorectal epithelium by Brachyspira species (B. aalborgi and B. pilosicoli), seen on biopsy as a fringe of organisms at the luminal border (a false brush border). It is usually an incidental finding, and its link with disease is uncertain.

It is found in 2% to 5% of colonoscopy biopsies in Western populations and up to 30% or more in tropical regions, and in 20% to 30% of men who have sex with men and of people with HIV. It is most often in the caecum and rectosigmoid.

Pathophysiology.

Spirochaetes attach end on to the colonic epithelium and may cause local inflammation and reduced absorption. Most carriers have no symptoms, and the organism can spread through faecal oral contact.

Most patients have no symptoms. Some have chronic watery diarrhoea, abdominal pain, bloating, rectal bleeding, mucus or weight loss, and some with spirochaetaemia (rare, in immunocompromised people) have fever.

Red flags.

• Weight loss with bleeding.
• Immunosuppression with severe diarrhoea.
• Positive blood cultures.

Colonoscopy usually looks normal. Biopsy shows a basophilic fringe on the epithelium on haematoxylin and eosin staining, confirmed with silver stains (Warthin-Starry) or immunohistochemistry, with PCR for species. Exclude other causes of the symptoms (inflammatory bowel disease, infection, irritable bowel syndrome, coeliac disease and cancer). Test for HIV and syphilis.

Differential diagnosis.

• Irritable bowel syndrome.
• Inflammatory bowel disease.
• Infectious colitis.
• Microscopic colitis.
• Sexually transmitted proctitis.
• Colorectal cancer.

Do not treat asymptomatic carriage. Treat patients with symptoms and no other cause with an antimicrobial course, and expect a variable response.

• Metronidazole: 400 to 500 mg orally three times daily for 10 days; maximum 1.5 g daily; monitor for neuropathy, nausea and alcohol intolerance; reduce to 500 mg twice daily in severe hepatic impairment, and avoid in the first trimester of pregnancy when possible.
• Azithromycin (alternative): 500 mg orally once daily for 5 days; maximum 500 mg daily; monitor QT interval and liver tests; avoid with other QT-prolonging drugs.

Treat coexisting HIV and sexually transmitted infection, and give partners advice.

Monitoring. Symptom review at 4 to 6 weeks; repeat biopsy only for persistent symptoms.

Referral and escalation. Gastroenterology; infectious disease for immunocompromised patients.