Clinical and pathologic features of fibrillary glomerulonephritis

A diagnosis of fibrillary glomerulonephritis was made in 31 renal biopsies from 28 patients on the basis of the electron microscopic identification of glomerular deposits of randomly arranged fibrils that resembled amyloidosis but were larger. This accounted for approximately 1% of all nontransplant renal biopsy diagnoses. Renal biopsy specimens with parallel arrays of 30 nm to 50 nm microtubules (that is, immunotactoid glomerulopathy) were not included in the study. The patients had a mean age of 49 years with a range of 21 to 75. The male to female ratio was 1:1.8 and the ratio of Whites to Blacks was 8.3:1, which differs from the 3:1 ratio in our overall biopsy population. All patients had proteinuria (mean 6.0 g/day), and most had hematuria and renal insufficiency. After a mean follow-up of 24 months, there was 48% renal survival. The light microscopic appearance of the fibrillary glomerulonephritis was quite varied. Capillary wall thickening and matrix expansion were the most frequent alterations. Nineteen percent of specimens had crescents. Morphometric ultrastructural analysis demonstrated a mean fibril diameter of 22.4 +/- 7.4 nm. Immunofluorescence microscopy revealed that IgG was the dominant and often the only immunoglobulin class in immune deposits, and subclass analysis revealed that IgG4 was the dominant or exclusive subclass in all specimens tested. We hypothesize that the relatively homogeneous nature of the immunoglobulin in the immune deposits is the basis for the fibril formation.