Whipple Disease with Concurrent Mycobacterium szulgai Infection: A Rare Diagnostic and Therapeutic Challenge

Whipple disease is a rare systemic infection caused by Tropheryma whipplei that often presents with nonspecific gastrointestinal symptoms and may mimic other disorders. We report the case of a 75-year-old woman with type 2 diabetes mellitus who presented with chronic diarrhoea and a 15 kg unintentional weight loss over 6 months despite preserved appetite. Laboratory investigations revealed iron-deficiency anaemia, hypoproteinaemia, mild inflammatory and liver function abnormalities, and peripheral eosinophilia. Extensive infectious, autoimmune, and gastrointestinal investigations were unrevealing. Abdominal computed tomography demonstrated mesenteric lymphadenopathy, raising suspicion for lymphoma. Histopathological examination of duodenal biopsies revealed numerous foamy macrophages containing periodic acid–Schiff-positive, diastase-resistant granular material, consistent with Whipple disease. Ziehl–Neelsen staining additionally demonstrated acid-fast bacilli, and subsequent investigations confirmed concomitant Mycobacterium szulgai infection. The significance of this finding remains uncertain, as it may represent either true coinfection or incidental colonisation. A potential explanation is that T. whipplei-induced macrophage dysfunction creates a permissive intracellular niche for nontuberculous mycobacteria, although supporting evidence is lacking. Following antimicrobial therapy, the patient experienced marked clinical improvement with resolution of symptoms and an 8 kg weight gain. This case highlights the diagnostic challenges of Whipple disease and the need to consider concomitant mycobacterial infection when acid-fast organisms are identified.