Most common site of biopsy in amyloidosis

Ref Robbins 9/e p261 Kidney. Amyloidosis of the kidney is the most common and most serious feature of the disease. Grossly, the kidney may appear unchanged, or it may be abnormally large, pale, gray, and firm; in long-standing cases, the kidney may be reduced in size. Microscopically, the amyloid deposits are found principally in the glomeruli, but they also are present in the interstitial peritubular tissue as well as in the walls of the blood vessels. The glomerulus first develops focal deposits within the mesangial matrix and diffuse or nodular thickenings of the basement membranes of the capillary loops. With progression, the deposition encroaches on the capillary lumina and eventually leads to total obliteration of the vas- cular tuft (Fig. 4-34, A). The interstitial peritubular deposits frequently are associated with the appearance of amorphous pink casts within the tubular lumens, presumably of a pro- teinaceous nature. Amyloid deposits may develop in the walls of blood vessels of all sizes, often causing marked vascular narrowing. renal biopsy is useful in the presence of urinary abnormalities. Rectal and gingival biopsy specimens contain amyloid in as many as 75% of cases with generalized amyloidosis. Examination of abdominal fat aspirates stained with Congo red is a simple, low-risk method. In suspected cases of AL amyloi- dosis, serum and urinary protein electrophoresis and immunoelectrophoresis should be performed.