Carcinoid tumor and the nephrotic syndrome: a novel association between neoplasia and glomerular disease.

Various malignancies are associated with the paraneoplastic evolution of the nephrotic syndrome. Renal biopsy in these instances frequently shows membranous glomerulonephritis. We describe a patient who had metastatic bronchial carcinoid tumor with development of microscopic hematuria and subsequent nephrotic syndrome in conjunction with another paraneoplastic process, a malignancy-related neuropathy. A decline in actual glomerular filtration rate led to percutaneous renal biopsy, which revealed fine holes in the glomerular basement membrane and focal capillary corrugation. Electron microscopy showed numerous small subepithelial dense deposits and fusion of foot processes, confirming the diagnosis of stage I membranous nephropathy. We believe this is the first published case of true carcinoid tumor associated with the nephrotic syndrome and a specific paraneoplastic glomerular lesion. Carcinoid tumor should be considered in the spectrum of malignancies associated with paraneoplastic development of the nephrotic syndrome.