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AL Amyloidosis — SCE Rheumatology MCQ

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HardConnective Tissue DiseaseAL AmyloidosisSCE Rheumatology

A 60-year-old man with long-standing rheumatoid arthritis, currently in sustained remission, develops progressive bilateral carpal tunnel syndrome. Examination shows macroglossia and periorbital purpura. Renal function is normal and there is no proteinuria. Serum protein electrophoresis shows no measurable paraprotein, but serum immunofixation detects a monoclonal lambda light chain and the serum free light-chain ratio is markedly abnormal. Which investigation is most appropriate next to establish the diagnosis and determine the amyloid type?

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Correct answer: C — Abdominal fat-pad aspiration plus bone marrow biopsy, with Congo red staining and amyloid typing

Macroglossia, periorbital purpura and bilateral carpal tunnel syndrome are characteristic red flags for systemic AL amyloidosis, while immunofixation and the markedly abnormal free light-chain ratio indicate an underlying monoclonal light-chain process. However, detection of a monoclonal protein does not itself prove that deposited amyloid is AL. Histological confirmation with Congo red and definitive amyloid typing are required. Abdominal fat-pad aspiration combined with bone marrow biopsy provides relatively low-risk tissue sampling and also evaluates the plasma-cell clone. Rheumatoid arthritis raises AA amyloidosis as a differential, making typing particularly important. Nerve conduction studies only quantify neuropathy; CT does not establish amyloid; SAP scintigraphy assesses systemic amyloid distribution but does not replace tissue confirmation or typing; repeat anti-CCP testing is irrelevant to this presentation.

Reference: Quarta CC et al. The value of screening biopsies in light-chain (AL) and transthyretin (ATTR) amyloidosis. European Journal of Haematology. 2020. https://pubmed.ncbi.nlm.nih.gov/32495369/