Case Report: Image-enhanced endoscopic characteristics of gastric amyloidosis with narrow-band imaging comparison

Gastrointestinal (GI) amyloidosis is a rare disorder with nonspecific clinical and endoscopic features, often leading to misdiagnosis. Timely recognition is crucial to prevent diagnostic delays and systemic complications.

A 64-year-old male initially presented with upper respiratory symptoms, and chest computed tomography (CT) performed for pneumonia evaluation incidentally revealed esophageal wall thickening. The first endoscopy showed diffuse redness with loss of the regular arrangement of collecting venules in the gastric body, and the findings were initially interpreted as Helicobacter pylori-associated gastritis. However, both gastric histopathology and the ¹³C urea breath test were negative, and no clear cause of erythema was identified. The patient's symptoms resolved after taking anti-inflammatory medication, and he did not return for follow-up as instructed. One year later, the patient developed proteinuria and bilateral lower extremity edema and was diagnosed with systemic light-chain (AL) amyloidosis involving the kidneys and heart. Repeat endoscopy revealed disc- and linear-shaped gastric erythema with a submucosal tumor (SMT)-like protrusion. Congo red staining with polarized light confirmed amyloid deposition in the gastric biopsy. In addition, we compared the endoscopic features of gastric erythema from three different etiologies. On narrow-band imaging (NBI), amyloid-related erythema showed a grayish-green signal with a more layered, deeper-appearing distribution, whereas vonoprazan-associated and Helicobacter pylori-associated erythema appeared more superficial with limited layering. Because absolute color intensity is not consistently comparable across panels, this observation should be considered hypothesis-generating rather than diagnostic.

This case highlights the diverse and potentially misleading endoscopic manifestations of GI amyloidosis. NBI may aid in visualizing the distribution pattern and apparent depth of amyloid-related mucosal signals and serve as a supportive diagnostic tool; however, histological confirmation via Congo red staining remains the gold standard. The combination of image-enhanced endoscopy, targeted biopsies, and multidisciplinary evaluation may facilitate earlier recognition and more comprehensive management of patients with atypical gastric erythema.