Glomerulopathies with fibrillary deposits.

Renal diseases involving glomerular deposits of fibrillary material are an important diagnostic challenge for the ultrastructural pathologist. Two primary disorders of this type, termed "fibrillary glomerulonephritis" (characterized by fibrils measuring approximately 20 nm in diameter) and "immunotactoid glomerulopathy" (characterized by larger, microtubular deposits), have been described. The possible relatedness of these two disorders and their potential association with other systemic illnesses are subjects of current debate. Other multisystemic diseases, including amyloidosis and various forms of cryoglobulinemia, can also present with fibrillary or microtubular deposits in the kidney. Five cases are presented in which fibrillar or microtubular structures were identified in renal biopsies by ultrastructural examination. The distinction between fibrillary glomerulonephritis, immunotactoid glomerulopathy, and other processes that have similar ultrastructural features are discussed.