1770 The Utility of Congo Red Staining in Grossly and Histopathologically Silent Gastrointestinal Amyloidosis

Abstract

INTRODUCTION: Primary amyloidosis (AL) with gastrointestinal (GI) involvement is a rare disease with nonspecific clinic manifestations1. Patients with symptoms suggestive of GI amyloidosis undergo endoscopic evaluation with biopsy and up to 75% of patients with GI amyloidosis have non-specific gross findings on endoscopy2. H&E staining shows characteristic amyloid deposition, which is then followed up by confirmatory Congo red staining. If both endoscopic and histologic evaluations are unremarkable, it is not common practice for Congo red staining to be performed3. We present two cases of AL amyloidosis with gastrointestinal involvement diagnosed by Congo red staining despite normal endoscopic findings and non-specific histopathologic findings. CASE DESCRIPTION/METHODS: 71-year-old female with history of smoldering myeloma and AL amyloidosis complicated by heart failure presented with several weeks of nausea, vomiting, abdominal pain and anorexia. Her symptoms were initially attributed to her chemotherapy regimen; however, they persisted despite reduction of her chemotherapy doses and addition of a protein pump inhibitor. She also developed new-onset dysphagia to solid foods. The patient was referred to gastroenterology for an esophagogastroduodenoscopy (EGD), which was grossly unremarkable. Biopsies showed only nonspecific chronic inflammation, yet Congo red staining was performed due to high clinical suspicion for amyloidosis and was positive. She was started on a dysphagia diet with eventual resolution of her symptoms. A similar case involved a 51-year-old female with history of AL amyloidosis complicated by gastroparesis with gastrostomy tube placement who presented for chronic diarrhea for 6 months. Workup including stool PCR studies, fecal fat, and stool alpha-1-antitrypsin were all negative. She was referred for EGD and colonoscopy which were grossly unremarkable. Histological evaluation of the biopsy was negative for significant pathologic changes (Figure 1A). However, she was found to have positive Congo red staining (Figure 1B). She underwent treatment with octreotide and psyllium with resolution of her symptoms. DISCUSSION: These two cases highlight the importance of performing Congo red staining in all cases in which there is high clinical suspicion for GI amyloidosis despite negative endoscopic and histopathologic evaluation. This method will allow for increased diagnosis and early treatment of the disease.