Primary Localized Small Bowel Amyloidosis: A Rare Cause of Diarrhea Detected by Balloon-Assisted Enteroscopy.

Gastrointestinal involvement occurs in approximately 4% of cases of systemic amyloidosis and may be associated with heterogeneous and nonspecific clinical manifestations and endoscopic findings, which poses important diagnostic challenges. A 76-year-old female with previous medical history of breast cancer, hypertension, dyslipidemia, asthma, and depression presented to emergency department with a 1-month history of diarrhea, abdominal pain, anorexia, asthenia, and weight loss. Physical examination revealed dehydration and abdominal tenderness. Stool microbiologic studies, toxin, fecal leukocyte count, stool fat, and celiac serology were all negative. Remarkably, an axillary lymphadenopathy was also noted and its investigation revealed multiple myeloma, which raised suspicion for gastrointestinal amyloidosis. However, upper digestive endoscopy and colonoscopy did not reveal abnormalities and both gastric and colon biopsies were negative for amyloid, as was abdominal fat biopsy. As the patient also presented hypoproteinemia and hypoalbuminemia suggestive of protein-losing enteropathy, videocapsule endoscopy was performed where petechiae, villous atrophy, and fissures were seen along jejunal mucosa. These findings were confirmed with double-balloon enteroscopy and jejunal biopsies revealed extensive deposition of an amorphous hyaline material in lamina propria and muscularis mucosae that exhibited apple-green birefringence under polarized light after Congo red staining, consistent with localized small bowel amyloidosis secondary to multiple myeloma. Chemotherapy was started, but she would die after 3 weeks. This case illustrates the role of balloon-assisted enteroscopy in diagnosis of localized small bowel amyloidosis with jejunal involvement.