Tuesday, December 17, 2013

Consult Rounds: Diabetic Fibrillosis- an entity that is forgotten?

This condition was first described in 1970 by Sohar et al when they observed small sized fibrils in the expanded mesangium of diabetic patients with nodular glomerulosclerosis.

This is interesting as in the realm of organized deposits, knowledge of this entity is important as we are embarking on biopsies of diabetics to look for alternate cause of proteinuria. The fibrils may appear to look like Fibrillary GN or Amyloidosis ( although slightly smaller).  To date, no clinical correlation has been noted when these fibrils are seen.

On LM, these fibrils are usually silver stain negative. The degree of decreased argyrophilia depends
on the extent of fibril deposition. The fibrils are only identifiable at the ultrastructural level and can measure from 5-20nm in diameter.  The fibrils are negative for Congo red and Thioflavins T and S.  The pathophysiology might be related to glycosylated expanded diabetic mesangium. Why some get it and some don’t is unclear.
 A nice review comparing organized deposits is presented in the pathology journal.

Amyloidosis is usually Congo red, Thioflavin T or S positive and the fibrils are  7- to 12-nm fibrils, randomly arranged.
Fibrillary GN is usually Congo red, Thioflavin T or S negative, IgG, C3 staining and nonbranching, 15- to 30-nm fibrils, randomly arranged;
Diabetic fibrillosis  is usually nodular GN; Congo red, Thioflavin T or S negative and IF shows linear IgG and albumin  on IF and fibrils are 5–25 nm in nodular mesangial areas
Immunotactoid GN is Congo red, Thioflavin T or S negative with variable microtubules stacked like deposits 10–90 nm

Image source: kidneypathology.com.ar

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