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Pathology · Immunopathology: AA amyloidosis
Sample itemA 45-year-old man with chronic osteomyelitis for 15 years develops nephrotic-range proteinuria and hepatosplenomegaly. A renal biopsy stained with Congo red shows apple-green birefringence under polarised light. What is the precursor protein of the deposits?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
B. Serum amyloid A, an acute-phase protein made by the liver under the influence of IL-6
Reactive (AA) amyloidosis complicates chronic inflammatory conditions such as osteomyelitis, tuberculosis, bronchiectasis and rheumatoid arthritis. IL-6 and IL-1 raise hepatic production of serum amyloid A, which is cleaved and deposited. The kidney is the commonest organ involved, and treating the underlying inflammation is the mainstay.
Option by option
A. Beta-2 microglobulin retained in renal failure
Beta-2 microglobulin forms amyloid in long-term dialysis patients, typically affecting joints and carpal tunnel.
B. Serum amyloid A, an acute-phase protein made by the liver under the influence of IL-6 (correct)
Correct. Serum amyloid A deposits in long-standing inflammatory disease.
C. Transthyretin made in the liver
Transthyretin forms familial and senile cardiac amyloid, not renal amyloid after chronic infection.
D. Monoclonal immunoglobulin light chains from clonal plasma cells
Light chains form AL amyloid and need a plasma cell dyscrasia, not chronic infection.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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