A 48-year-old Samoan man underwent a colonoscopy and endoscopy to evaluate a history of chronic diarrhea and recent significant weight loss of >20 kilograms. His past medical history was significant for recurrent polyarticular gout for >7 years, which had caused significant physical impairment. On clinical examination his weight was 84 kg (body mass index, 25 kg/m2). Inspection of the hands revealed swelling and enlargement of the proximal interphalangeal joints, and a gouty tophus was visible on the tragus of the right ear. The systemic examination was otherwise normal.
Biochemical analysis showed mild anemia (124 g/L) and leukocytosis (12.7 x 109/L) with lymphocytosis (5.75 x 109/L). C-reactive protein was elevated at 71 mg/L. Liver function tests showed elevated alkaline phosphotase (351 U/L) and gamma-glutamyl transpeptidase (277 U/L) with hypoalbuminemia (25 g/L). The urate level was 0.68 mmol/L, and microbiological investigations of stool samples were negative. A joint aspiration showed negatively birefringent monosodium urate crystals with sterile cultures. A liver ultrasound was normal.
Esophagogastroduodenoscopy identified gastric mucosal atrophy and blunted villi in the duodenum (Figure 1). Duodenal mucosal biopsies showed preserved villous architecture with some deposition of eosinophilic material within the lamina propria and vessel walls. The eosinophilic material stained positive with Congo red (Figure 2). A colonoscopy was macroscopically normal. Biopsies from the terminal ileum showed mild villous blunting, fibrosis of submucosa, and eosinophilic material that stained positive with Congo red within the lamina propria and vessel walls. Immunohistochemistry of duodenal and terminal ileum sections tested positive for serum AA protein. Kappa and lambda immunoglobulin light chain and transthyretin immunohistochemical stains were negative. Proteomic analysis demonstrated the amyloid deposits to be comprised of serum amyloid A (SAA)-2 protein.
The results were consistent with a diagnosis of AA amyloidosis. A search for additional causes of secondary amyloidosis failed to identify any other immune-mediated diseases such as rheumatoid arthritis or chronic infections including tuberculosis. Thus, the final diagnosis was systemic AA amyloidosis with GI involvement due to polyarticular tophaceous gout.
Echocardiogram and cardiac magnetic resonance imaging showed no evidence of cardiac amyloid infiltration, and renal investigations revealed proteinuria of 450 mg/day with normal glomerular filtration rate (GFR). The patient was commenced on a weaning course of prednisolone, and colchicine was started at 500 mug. His dose of allopurinol was increased from 100 mg to 300 mg once daily. During outpatient follow-up, he reported that the GI symptoms had started to improve gradually following the resolution of the gout exacerbations.