Human intestinal spirochetosis and proctitis in the context of acute cytomegalovirus infection: a case report and review of the literature

Abstract

Introduction: Prevalence of sexually transmitted infections, including those affecting the rectum and presenting as proctitis, is increasing worldwide. Diagnostic evaluation may be particularly challenging when serological findings are negative or when concomitant infections are present.

Case Presentation: A 44-year-old man who has sex with men presented with persistent fever and watery diarrhea. Initial evaluation revealed elevated inflammatory markers, hepatosplenomegaly, lymphocytosis, mild hepatocellular injury, and computed tomography findings suggestive of rectosigmoid colitis. Extensive microbiological, immunological, and hematological investigations supported the diagnosis of acute cytomegalovirus infection. Serological testing for syphilis was negative. Since the patient was immunocompetent and gastrointestinal symptoms could not be fully explained by cytomegalovirus (CMV) infection alone, flexible sigmoidoscopy with biopsies was performed. Endoscopy showed edematous rectosigmoid mucosa without ulcerations. Histopathological examination revealed superficial epithelial injury with preserved crypt architecture, focal cryptitis, occasional crypt abscesses, and mixed inflammatory infiltrates. Immunohistochemical staining was strongly positive for Treponema pallidum. However, in the context of negative syphilis serology and compatible histopathological features, this finding was interpreted as cross-reactivity associated with human intestinal spirochetosis. The patient was treated with intramuscular benzathine penicillin G, followed by normalization of bowel habits.

Conclusions: This case illustrates the diagnostic complexity of proctitis in an immunocompetent MSM patient with acute CMV infection and human intestinal spirochetosis. It emphasizes that positive anti-Treponema pallidum immunohistochemistry should not be interpreted in isolation, as cross-reactivity with intestinal spirochetes may lead to overdiagnosis of gastrointestinal syphilis. Careful clinicopathological correlation remains essential when routine diagnostic findings are inconclusive or potentially misleading.