73-year-old male developed a nephrotic syndrome after diagnosis of a plasma cell myeloma (multiple myeloma) two years prior (specimen from autopsy).
- A section of the kidney is shown with clearly discernible cortex and medulla.
- Glomeruli show widespread depositions of homogenous Congo red positive material in capillary loops and mesangium. Part of the glomerular structure is destroyed.
- Small arteries and arterioles also display Congo red positive deposits. (In both glomeruli and arteries amyloid is localized subendothelially by electron microscopy).
- In addition, interstitial Congo red positive deposits are also present.
- Lumen of tubules show partly calcified protein casts.
- A marked interstitial fibrosis and tubular atrophy are noted.
Macroscopy: Appearance of kidneys may be unchanged. Kidneys may also be enlarged, firm, pale and of grayish color. In long-standing cases the size may be reduced due to scarring.
Immunhistochemistry: Amyloid in this case is composed of monoclonal light chains (AL amyloid).