Amyloidosis light chain (AL) amyloidosis with gastrointestinal involvement: diagnostic value of endoscopy in systemic diseases.

Intestinal amyloidosis is an uncommon form of systemic amyloidosis characterized by the extracellular deposition of misfolded immunoglobulin light chains in the gastrointestinal tract, causing structural and functional damage. Its clinical presentation is usually nonspecific, which complicates diagnosis and leads to underdiagnosis. The most common form of systemic amyloidosis is primary amyloidosis or AL amyloidosis, which, although usually presenting in isolation, is associated with plasma cell dyscrasias in up to 10-15% of cases, especially multiple myeloma. Diagnosing this association is even more complex in cases where the disease begins in the gastrointestinal tract. In these cases, gastroscopy with biopsies is the essential technique to identify findings suggestive of amyloid infiltration and confirm the histological diagnosis using Congo red staining and immunohistochemistry for light chains. We present the case of a 76-year-old woman without relevant medical history who was admitted with the onset of heart failure. Transthoracic echocardiography showed marked hypertrophy of the interventricular septum, suggesting a deposition disease, and serum protein immunoelectrophoresis revealed elevated levels of free kappa light chains. During her hospitalization, the patient developed melena and anemia, leading to urgent gastroscopy, which revealed patchy areas of erythematous and edematous tissue in the duodenum. Biopsies demonstrated submucosal deposits of amorphous material with apple-green birefringence on Congo red staining and positive immunohistochemistry for kappa light chains, confirming the diagnosis of AL amyloidosis. Subsequently, a bone marrow biopsy revealed diffuse infiltration by plasma cells, leading to a diagnosis of multiple myeloma with AL amyloidosis involving the heart and intestine.