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Differential Diagnosis of Fibrillary Glomerulopathies

Posted Jan 19 2009 12:00am
The finding of fibrils on electron microscopy of a renal biopsy specimen may be an extremely important clue in establishing the diagnosis.  In fact, for many of the conditions listed below, the diagnosis may be based PURELY on a detailed ultrastructural characterization of the fibril, as in fibrillary or immunotactoid glomerulopathy.  

The first step in the differential diagnosis of fibrillary glomerulopathies is to divide the condition into an IMMUNOGLOBULIN-MEDIATED versus a NON-IMMUNOGLOBULIN MEDIATED process, which is typically done by immunofluorescent staining against different heavy and light chain classes.

IMMUNOGLOBULIN-MEDIATED fibrillary glomerulopathies include:
-AL amyloidosis.
-MIDD (monoclonal immunoglobulin deposition disease).
-type 2 cryoglobulinemia.
-immunotactoid glomerulopathy (see picture)
-fibrillary glomerulopathy.

NON-IMMUNOGLOBULIN-MEDIATED fibrillary glomerulopathies include:
-AA amyloidosis.
-fibronectin glomerulopathy.
-diabetic fibrillary glomerulopathy.
(note:  the latter two on this list are pretty rare).

Another crucial distinction here is whether the biopsy specimen stains negative or positive for CONGO RED (indicating the beta-pleating sheet structure of precipitated amyloid protein).  
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