Glomerulopathies with fibrillary deposits

Renal diseases involving glomerular deposits of fibrillary material are an important diagnostic challenge for the ultrastructural pathologist. Two pri mary disorders of this type, termed "fibrillary glomerulonephritis" (charac terized by fibrils measuring approximately 20 nm in diameter) and "immunota ctoid glomerulopathy" (characterized by larger, microtubular deposits), hav e been described. The possible relatedness of these two disorders and their potential association with other systemic illnesses are subjects of curren t debate. Other multisystemic diseases, including amyloidosis and Various f orms of cryoglobulinemia, can also present with fibrillary or microtubular deposits in the kidney. Five cases are presented in which fibrillar or micr otubular structures were identified in renal biopsies by ultrastructural ex amination. The distinction between fibrillary glomerulonephritis, immunotac toid glomerulopathy, and other processes that have similar ultrastructural features are discussed.