AL-amyloidosis of the kidney initially presenting as minimal change glomerulonephritis

Small amounts of amyloid in kidney biopsy specimens may be missed on routin e examination unless specifically targeted. Occasionally, this oversight re sults in a diagnosis of minimal change glomerulonephritis (MCGN). This misd iagnosis may be facilitated by the fact that typical "minimal changes" with flattening and effacement of the epithelial foot processes can be found in capillary loops directly affected by amyloid deposition as well as in capi llary loops of glomeruli with only mild amyloid deposition in the mesangium . Repeatedly, the diagnosis of MOON had to be corrected to renal amyloidosi s when re-examination by special techniques succeeded in detecting even sma ll amounts of amyloid fibrils. We present the case of a previously healthy 49-year-old man who suddenly developed nephrotic syndrome. A first renal bi opsy showed MOON. Proteinuria remained refractory to immunosuppressive trea tments, and creatinine clearance deteriorated rapidly. Two years later, a r epeat renal biopsy showed AL-amyloidosis. In this case, re-examination of t he first biopsy in the light of the final diagnosis again did not show any deposition of amyloid fibrils. We suspect that proteinuria and epithelial p odocyte changes in amyloidosis are caused by factors other than deposition of amyloid fibrils itself. Possibly a cytokine release during the early fib ril formation leads to abnormalities even before the typical structural cha nges of renal amyloidosis can be detected. This is analogous to the hypothe sis of a circulating factor that leads to proteinuria in focal segmental gl omerulosclerosis or the speculation of altered lymphokine expression associ ated with the development of MOON in Hodgkin's disease. (C) 2000 by the Nat ional Kidney Foundation, Inc.