A 58-year-old man with a 10-year history of rheumatoid arthritis presents with nephrotic syndrome and hepatomegaly. Kidney biopsy shows apple-green birefringence under polarized light after Congo red staining. Which is the most common type of amyloid deposited in this patient?

Explanation

## Amyloid Type in Chronic Inflammatory Disease **Key Point:** AA amyloid (serum amyloid A) is the most common type of amyloid associated with chronic inflammatory conditions, particularly rheumatoid arthritis. ### Pathophysiology In chronic inflammation (RA, tuberculosis, chronic osteomyelitis, inflammatory bowel disease), persistent elevation of serum amyloid A (an acute-phase reactant) leads to misfolding and deposition of AA amyloid fibrils in target organs. ### Clinical Context - **Rheumatoid arthritis** is the classic setting for secondary (AA) amyloidosis in developed countries - Typically manifests as nephrotic syndrome (glomerular deposition) and hepatomegaly - Occurs after years of active disease (usually >10 years) ### Amyloid Type Classification | Amyloid Type | Precursor Protein | Common Associations | Organs Affected | |---|---|---|---| | **AA** | Serum amyloid A | RA, TB, chronic osteomyelitis, IBD | Kidney, liver, spleen | | AL | Immunoglobulin light chains | Multiple myeloma, primary amyloidosis | Heart, kidney, nerves, GI | | AβM | β2-microglobulin | Chronic hemodialysis (>5 years) | Joints, bones, carpal tunnel | | Aβ | β-amyloid peptide | Alzheimer disease | Brain | **High-Yield:** AA amyloidosis is **secondary amyloidosis** — it develops as a complication of chronic systemic inflammation. AL amyloidosis is **primary amyloidosis** — it arises de novo from clonal plasma cell disease. **Clinical Pearl:** The Congo red stain with apple-green birefringence under polarized light is pathognomonic for amyloid (any type); the specific type requires immunohistochemistry or mass spectrometry. **Mnemonic: AA = Acquired secondary (chronic inflammation); AL = Abnormal primary (Light chains)**