A 58-year-old man with a 10-year history of rheumatoid arthritis presents with nephrotic syndrome and hepatomegaly. Kidney biopsy shows amyloid deposition. Which is the most common type of amyloidosis in this clinical scenario?

Explanation

## Clinical Context This patient has chronic rheumatoid arthritis complicated by nephrotic syndrome and hepatomegaly — a classic presentation of secondary (AA) amyloidosis. ## AA Amyloidosis: The Most Common Secondary Form **Key Point:** AA amyloidosis is the most common type of amyloidosis worldwide and accounts for ~60% of all amyloidosis cases in endemic regions. It is derived from serum amyloid A (SAA), an acute-phase reactant. **High-Yield:** AA amyloidosis is associated with chronic inflammatory conditions: - Rheumatoid arthritis (most common in developed countries) - Tuberculosis (most common in endemic regions) - Chronic osteomyelitis - Inflammatory bowel disease - Chronic infections (leprosy, bronchiectasis) ## Comparison of Major Amyloidosis Types | Type | Precursor Protein | Primary Association | Epidemiology | |------|-------------------|----------------------|---------------| | **AA** | Serum amyloid A | Chronic inflammation (RA, TB, infection) | Most common globally | | AL | Immunoglobulin light chain (κ or λ) | Plasma cell dyscrasia, multiple myeloma | Most common in developed countries (primary) | | AβM | β2-microglobulin | Chronic hemodialysis (>5 years) | Dialysis-associated amyloidosis | | Aβ2M | Apolipoprotein A-II | Familial, hereditary | Rare | ## Pathophysiology of AA Amyloidosis 1. **Chronic inflammation** → persistent elevation of serum amyloid A (SAA) 2. **Proteolytic cleavage** of SAA by macrophage elastase 3. **Misfolding and polymerization** of the N-terminal fragment (76 amino acids) 4. **Deposition** in kidneys (glomeruli), liver, spleen, and heart **Clinical Pearl:** The nephrotic syndrome in this case results from glomerular amyloid deposition, typically affecting the glomerular basement membrane and mesangium. Hepatomegaly occurs due to amyloid infiltration of hepatic sinusoids. **Mnemonic:** **AAAA** — **A**cute phase protein → **A**myloid **A** → **A**ssociated with chronic **A**rticular/inflammatory disease ## Diagnostic Confirmation - **Congo red staining** of kidney biopsy shows apple-green birefringence under polarized light - **Immunohistochemistry** or **mass spectrometry** confirms AA type - **Serum amyloid A levels** are elevated in active disease **High-Yield:** AA amyloidosis is potentially reversible if the underlying inflammatory condition is controlled (e.g., TNF inhibitors in RA, anti-TB therapy in tuberculosis). This distinguishes it from AL amyloidosis, which is generally progressive.