Immune-complex glomerulonephritis in a patient with mixed connective tissue disease.

Renal involvement and hypocomplementemia in mixed connective tissue disease are reported to be rare. A patient is described here with mixed connective tissue disease and persistently low serum C'3 levels in whom renal insufficiency and nephrotic syndrome developed secondary to immune-complex glomerulonephritis. Light microscopy of the renal biopsy specimen showed predominantly a membranous lesion. Immunofluorescent staining showed granular deposition along the basement membrane of immunoglobulin G, immunoglobulin M, fibrinogen and C3. Electron microscopy showed numerous electron-dense deposits along the glomerular capillary membrane and in the mesangium.