L LSUHSC-S Renal Pathology Consultative Services

Interesting Case

Case Study #: 3

08/03/09

By: Stephen M. Bonsib, M.D.

Xin Gu, M.D.

Ami Bhalodia, M.D.

318-675-4557 phone

318-675-4541 fax

sbonsi@lsuhsc.edu

Clinical History:

Patient presented with renal failure, creatinine of 3.4 and 1+ proteinuria.

Past medical history: diabetes and multiple myeloma.

Case courtesy of Glenn McDonald, MD

Figure 1: H&E

Figure 2:

Mesangial matrix increase on PAS

Figure 3:

Ropey to coarse reaction for IgG (and C3, kappa and lambda - not shown) within capillary loop and mesangial regions

Figure 4: Electron microscopy showing 12-25nm fibrils

Question:

1.
The light microscopy reveals focal thickening of peripheral capillary loops and mesangial area expansion without significant hypercellularity. The EM shows randomly arranged fibrils in the
capillary loops and mesangial regions. The differential diagnosis based on these findings would include both Congo-red positive fibrillary glomerulopathies like amyloidosis and Congo-red negative glomerular diseases such as fibrillary glomerulonephritis, immunotactoid glomerulonephritis, fibronectin glomerulopathy and collagenofibrotic glomerulopathy. However, the size of the fibrils in this case (12-25nm), the random arrangement within mesangial areas and peripheral capillary loops, along with the coarse and ropy ribbon-like reaction of IgG and C3 on IF is characteristic of Fibrillary GN.
2.
The Congo red and Thioflavin stains would be negative in this case.
3.
It was first described by Rosenmann and Eliakim in 1977 as an amyloid-like glomerulopathy but with negative congo red staining. It is characterized by the deposition of fibrils in the mesangium and GBM. The light microscopic findings can resemble membranous GN, membranoproliferative GN, and at times, FSGS. The fibrils are generally less than 30 nm in diameter, with the majority measuring approximately 20 nm. The pathogenesis of FibGN is not clearly understood at present. Immunofluorescence findings suggest an immunogenic origin. There in no definitive treatment for this condition. Half of all cases develop end stage renal failure within 4 years of diagnosis.