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

Small amounts of amyloid in kidney biopsy specimens may be missed on routine examination unless specifically targeted. Occasionally, this oversight results in a diagnosis of minimal change glomerulonephritis (MCGN). This misdiagnosis 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 capillary loops of glomeruli with only mild amyloid deposition in the mesangium. Repeatedly, the diagnosis of MCGN had to be corrected to renal amyloidosis when re-examination by special techniques succeeded in detecting even small amounts of amyloid fibrils. We present the case of a previously healthy 49-year-old man who suddenly developed nephrotic syndrome. A first renal biopsy showed MCGN. Proteinuria remained refractory to immunosuppressive treatments, and creatinine clearance deteriorated rapidly. Two years later, a repeat renal biopsy showed AL-amyloidosis. In this case, re-examination of the first biopsy in the light of the final diagnosis again did not show any deposition of amyloid fibrils. We suspect that proteinuria and epithelial podocyte changes in amyloidosis are caused by factors other than deposition of amyloid fibrils itself. Possibly a cytokine release during the early fibril formation leads to abnormalities even before the typical structural changes of renal amyloidosis can be detected. This is analogous to the hypothesis of a circulating factor that leads to proteinuria in focal segmental glomerulosclerosis or the speculation of altered lymphokine expression associated with the development of MCGN in Hodgkin's disease.