Renal Amyloidosis
Renal involvement is a common and serious complication of systemic amyloidosis. It typically presents as nephrotic syndrome due to the extracellular deposition of misfolded proteins in the glomerulus.
1. Pathological Features
| Examination | Findings |
|---|---|
| Light Microscopy (LM) | Amorphous, eosinophilic, acellular material in the mesangium and capillary loops. |
| Staining | Congo Red stain shows apple-green birefringence under polarized light. |
| Electron Microscopy (EM) | Randomly arranged, non-branching fibrils (8–10 nm in diameter). |
2. Exam Must-Knows
- Types of Amyloid:
- AL Amyloidosis: Associated with plasma cell dyscrasias (e.g., Multiple Myeloma). Derived from immunoglobulin light chains.
- AA Amyloidosis: Secondary to chronic inflammatory conditions (e.g., Rheumatoid Arthritis, IBD, Osteomyelitis). Derived from serum amyloid A (SAA).
- Presentation: Often presents with nephrotic-range proteinuria and, in advanced cases, enlarged, pale kidneys on ultrasound.
Pathology Board Hint: For board examinations, if a patient with a known chronic inflammatory disease or multiple myeloma develops nephrotic syndrome, think amyloidosis. The “apple-green birefringence” is the classic buzzword you should look for.