Fibrillary glomerulonephritis associated with essential thrombocytosis.

A 68-year-old man with a 30-year history of essential thrombocytosis developed nephrotic syndrome. Renal biopsy showed massive deposits of Congo red-negative periodic acid Schiff (PAS)-positive substance in the mesangium and capillary wall that was positive for IgG. Electron microscopic examination revealed 10- to 20-nm fibrils in the deposits, and there was no other organ involvement; thus, we diagnosed fibrillary glomerulonephritis.