Rare primary small intestinal infection: a case report of Mycobacterium kansasii enteropathy in an immunocompetent patient and literature review.

Background

Non-tuberculous mycobacteria (NTM) are important opportunistic pathogens that most commonly infect the lungs. Primary involvement of the gastrointestinal tract-especially the small intestine-is exceedingly rare, and small-bowel infection caused by Mycobacterium kansasii (M. kansasii) has seldom been reported. CASE PRESENTATION We describe an extremely rare case of primary small-intestinal M. kansasii infection in an immunocompetent young man who presented with prolonged chronic diarrhea and fever. After an extensive but unrevealing diagnostic work-up, the etiology was finally established by microbial metagenomic sequencing of tissue obtained by double-balloon endoscopy. Building on the initial regimen of ethambutol hydrochloride, rifampicin, and clarithromycin-and with subsequent antibiotic adjustments tailored to the patient's evolving symptoms-clinical symptoms resolved completely, and follow-up endoscopy showed mucosal improvement.

Conclusion

This case underscores that NTM infection should be considered in the differential diagnosis of unexplained chronic gastrointestinal symptoms and highlights the pivotal role of modern molecular techniques in reaching a precise diagnosis. Detailed analysis of the case together with a review of the literature aims to raise clinicians' awareness and improve management of this rare entity.