Giardia lamblia Mimicking Celiac Disease in an Immunocompromised Patient: A Case Report.

Giardia lamblia infection can clinically and histopathologically mimic celiac disease. This challenge is particularly pronounced in immunocompromised patients, where serological tests may be negative and mucosal changes more exaggerated. A 52-year-old female with immunodeficiency presented with chronic diarrhea unresponsive to a gluten-free diet. Initial duodenal biopsies were reported as Marsh 3b, and celiac disease was considered in the first place despite negative serology. The first stool examination was negative for parasites. On repeat endoscopy, duodenal nodularity with intraepithelial lymphocytosis and nodular lymphoid hyperplasia was observed. Careful re-evaluation of biopsy slides and subsequent stool examination revealed G. lamblia trophozoites, confirming the diagnosis. Immunodeficiency complicated the diagnostic process by reducing antibody production, resulting in negative serology, and by allowing chronic infection to induce celiac-like mucosal alterations. Moreover, the initial false-negative stool test and elevated fecal calprotectin levels further suggested inflammatory bowel disease, adding to the diagnostic challenge. In patients with persistent symptoms despite adherence to a gluten-free diet, before diagnosing refractory celiac disease, parasitic agents particularly G.lamblia should be excluded in the first place. Repeated stool examinations and meticulous histopathological evaluation of duodenal biopsies are crucial for reaching the correct diagnosis.