There are a number of glomerulopathies that feature organized deposits of nonbranching fibrils, some more common than others. The diseases make their first major separation into Congo Red positive (amyloid) and Congo Red negative categories. Amyloid fibrils are randomly arranged, and are 8-12nm in diameter. The Congo Red negative fibrillary diseases are more diverse, and since they are more rare but are favored by those who write the boards, I found a review to be helpful. Fibrillary Glomerulonephritis:
- Randomly arranged fibrils 12-30nm in diameter
- Usually polyclonal IgG
- Presents usually with proteinuria. 50% have nephrotic syndrome at presentation.
- 50% of patients progress to ESRD within a few years
- Treatment often unsuccessful. Steroids, cytoxan, and rituxan have been used with varying success.
- Does not usually recur in transplants
- parallel deposits of straight, hollow-lumen fibrils (microtubules) >30nm in diameter
- usually monoclonal IgG
- usually secondary
- Deposits occur on subepithelial surface of basement membrane, can be indistinguishable from membranous on light microscopy
- Presents with nephrotic syndrome, hypertension, hematuria.
- Recurs in transplants
- randomly arranged curved microtubules 25-35nm in diameter
- 10-15nm fibrils
- Hereditary, autosomal dominant
- Presents with proteinuria, hematuria, hypertension
- Banded collagen fibrils
- Hereditary, autosomal recessive, most cases from Japan
- Presents with edema and nephrotic syndrome
- Progresses to ESRD
Diabetes can also be associated with fibril deposition, usually 5-20nm in diameter. Lupus can cause fibril formation, and these generally are around the same size as the deposits in fibrillary GN and are arranged in a fingerprint pattern.This article contains an outstanding flow chart for the differential diagnosis of glomerular diseases with organized deposits.
For the boards, it may be helpful to remember that the fibril diameter of the more common fibrillary diseases- amyloid, fibrillary GN, and immunotactoid GP are correlated with their position in the alphabet- (A= 8-12nm, F= <30nm, usually 18-20, and I= >30nm, usually 45-55nm).