Resolution of renal amyloidosis secondary to rheumatoid arthritis

A patient with seronegative rheumatoid arthritis developed a nephrotic syndrome. Histological examination of renal biopsy disclosed moderate amyloidosis. Ultrastructurally the glomerular amyloid deposits were seen to be located both within the mesangium and subepithelially in the peripheral capillaries. The patient was treated with prednisone and cyclophosphamide for two years. The nephrotic syndrome remitted and a follow-up biopsy showed almost total disappearance of Congo red positive amyloid substance. Electron microscopy showed abundant finely granular material but only small amounts of fibrillar amyloid in the mesangial regions and intramembranous lucent areas containing few amyloid fibrils but no subepithelial deposits in the peripheral capillaries. We conclude that the mesangial amyloid substance was degraded to granular material and that the subepithelial amyloid deposits were resolved by mechanisms similar to those involved in the resolution of subepithelial immune complex deposits, i.e. through slow washing out and incorporation into the basement membrane.