Atypical Manifestation of Giardiasis: Exocrine Pancreatic Insufficiency in a Young Adult.

Diagnosing the underlying cause of chronic diarrhea in adults can be complex, especially when routine evaluations yield no clear etiology. Although Giardia lamblia is a common pathogen, its role in triggering secondary complications such as exocrine pancreatic insufficiency (EPI) is rarely recognized. Increased awareness of this association is crucial as newer diagnostic tools become more accessible in outpatient settings. We report a case of a 22-year-old male with five months of persistent watery diarrhea and abdominal discomfort following a course of clindamycin. Initial laboratory and stool studies were unrevealing, but fecal elastase-1 levels were severely reduced, consistent with EPI. The patient showed partial improvement with pancreatic enzyme replacement and cholestyramine. A multiplex polymerase chain reaction (PCR) stool panel later identified Giardia lamblia, and treatment with tinidazole resulted in the resolution of symptoms. This case illustrates a rare but important association between chronic giardiasis and reversible EPI. Giardia-induced disruption of the duodenal mucosa can impair enteroendocrine signaling and pancreatic stimulation, even in the absence of intrinsic pancreatic disease. Standard antigen testing may miss the diagnosis due to intermittent cyst shedding; multiplex molecular diagnostics offer improved sensitivity. Clinicians should maintain a broad differential in chronic diarrhea and consider early pancreatic evaluation when malabsorptive features are present. Early use of fecal elastase testing and molecular stool diagnostics in patients with persistent diarrhea can uncover overlooked but treatable conditions like Giardia-associated EPI. This comprehensive approach enables more accurate diagnosis, prompt treatment, and prevention of long-term nutritional and gastrointestinal complications.