Association of retroperitoneal fibrosis and interstitial nephritis.

A patient with renal failure and light-chain proteinuria showed roentgenographic evidence of retroperitoneal fibrosis on further examination. Diffuse hyperglobulinemia, low levels of C3 and C4, and elevated C1q binding were noted. Biopsy specimens of the kidney and retroperitoneal tissue disclosed a dense pleomorphic cellular infiltrate with a preponderance of plasma cells. Renal function improved slowly after ureterolysis and institution of prednisone therapy. The case emphasizes the immunologic features of the early phase of idiopathic retroperitoneal fibrosis.