Serum amyloid A (SAA)-derived amyloid (AA amyloidosis) deposits preferentially in which organs and in which pattern on Congo red staining?

• A Heart and peripheral nerves; metachromasia with crystal violet
• B Spleen, kidney, liver; apple-green birefringence under polarized light ✓
• C Brain; neuritic plaques and tauopathy
• D Tongue and heart; positive thioflavin T fluorescence only

Explanation

AA amyloidosis (reactive systemic amyloidosis) complicates chronic inflammatory diseases (TB, RA, FMF, osteomyelitis); SAA is an acute-phase reactant cleaved to amyloid A fibrils. Deposits occur in spleen (perifollicular — 'sago spleen'; diffuse red — 'lardaceous spleen'), kidney (leading to nephrotic syndrome), and liver sinusoids. All amyloid types show green birefringence under polarized light after Congo red staining (pathognomonic). AL amyloidosis (immunoglobulin light chains) commonly affects heart and peripheral nerves. Beta-amyloid in Alzheimer's disease is a separate amyloid type. Thioflavin T fluorescence is used for detection but is not specific for distribution pattern.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.