Capsule Endoscopy-Guided Diagnosis of Small Bowel Lymphoma Presenting as Protein-Losing Enteropathy: Complementary Role of Peripheral Blood Flow Cytometry.

Protein-losing enteropathy (PLE) is an uncommon and often underrecognized manifestation of lymphoproliferative disorders and may be difficult to diagnose when conventional gastrointestinal investigations are unrevealing. We present an 82-year-old woman with recurrent hospital admissions initially spanning six months for diarrhea, weight loss, peripheral edema, and persistent hypoalbuminemia. Initial upper gastrointestinal endoscopy was normal, and colonoscopy was deferred due to intercurrent infection. Despite extensive laboratory and radiologic evaluation, including routine biochemical testing and imaging, the etiology of PLE remained unclear. Peripheral blood flow cytometry subsequently identified a small kappa-restricted monoclonal B-cell population compatible with marginal zone lymphoma, later confirmed on bone marrow biopsy, raising suspicion for gastrointestinal involvement. Video capsule enteroscopy demonstrated diffuse erosive and ulcerative disease throughout the small intestine, providing an anatomical explanation for the patient's protein loss. Following lymphoma-directed therapy, repeat capsule enteroscopy showed complete normalization of the small bowel mucosa. This case highlights the diagnostic value of combining peripheral blood flow cytometry and capsule endoscopy in unexplained protein-losing enteropathy, a rare and diagnostically challenging presentation of indolent lymphoma, and illustrates the role of capsule imaging in both disease localization and treatment monitoring. As a single-case report, these findings are not generalizable, and further studies are required to evaluate the broader applicability of this diagnostic approach.