Case Report: A rare case of small intestinal light-chain amyloidosis

Systemic light-chain (AL) amyloidosis is a rare plasma cell disorder characterized by aberrant light chain deposition and progressive organ dysfunction. Isolated gastrointestinal involvement is extremely rare, and is prone to delayed diagnosis due to atypical and nonspecific abdominal symptoms. We herein describe a 66-year-old female patient presenting with a 3-month history of simple epigastric pain. Endoscopic examination revealed diffuse fragile erosions, multiple ulcers, and scattered hematomas in the duodenum and jejunum. Histopathological analysis with Congo red staining and polarized light microscopy confirmed amyloid deposition with characteristic apple-green birefringence. Light-chain immunohistochemistry on intestinal tissue showed a small proportion of infiltrating plasma cells with κ positivity and a larger population of plasma cells with λ positivity. Bone marrow trephine biopsy immunohistochemistry demonstrated plasma cells positive for λ and negative for κ light chains. Further immunological and serological tests verified monoclonal IgG- λ restriction, markedly elevated λ free light chains, and a decreased κ / λ ratio, confirming the diagnosis of primary λ -type AL amyloidosis. The patient received daratumumab, bortezomib, and dexamethasone therapy. Post-treatment follow-up demonstrated an excellent hematologic response, including normalized serum free light chain ratio, and negative urine immunofixation electrophoresis, while serum immunofixation electrophoresis remained weakly positive. There is no sign of involvement in other organs after a 23-months follow-up. This atypical case exhibited an extremely rare phenotype of systemic AL amyloidosis with isolated gastrointestinal manifestation. Early endoscopic biopsy and standardized anti-plasma cell therapy are critical to block amyloid accumulation, prevent irreversible multi-organ damage, and improve long-term prognosis.