Systemic amyloidosis with gastrointestinal involvement: Diagnosis from endoscopic and histological views

Amyloid tends to deposit in the gastrointestinal tract, which, being easily accessible, is often the target organ for a pathological diagnostic examination. Although a mucosal biopsy is necessary for a definitive diagnosis and several studies have reported positive results for each possible biopsy site, there remain many unclear features in various aspects. This review focuses on the current literature to determine a better understanding of the diagnosis from endoscopic and histological views in patients with systemic amyloidosis with gastrointestinal involvement. A literature search was performed using PubMed to identify relevant studies; linked references were also reviewed. Endoscopic findings vary based on the organ and the depositing amyloids. A fine granular appearance or polypoid protrusions are likely to occur in the duodenum. AL, Aβ2M, and ATTR amyloids are likely to deposit submucosally, while AA amyloid is easily deposited in the superficial layer of the mucous membrane. Furthermore, it is necessary to consider the collection of biopsy specimens from the duodenum, which has high positive biopsy rates. However, the difference in the positive biopsy rates depends on whether endoscopic findings are available or whether the appropriate number has not been fully elucidated. A duodenal biopsy is strongly recommended to confirm the deposition of amyloid in patients with systemic amyloidosis having gastrointestinal involvement. Because amyloidosis is a disease with a poor prognosis, early diagnosis and treatment are required; gastroenterologists and endoscopists play important roles.