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?

Question

Accepted Answer

C. AA amyloid (serum amyloid A). ## 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)**

Answer

A. AL amyloid (light chain)

Answer

B. AβM amyloid (β2-microglobulin)

Answer

D. Aβ amyloid (β-amyloid peptide)

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

Pathophysiology

Clinical Context

Amyloid Type Classification

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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