Dr Franco Ferrario Renal Immunopathology Center San Carlo Borromeo Hospital Milan, Italy

 

 

Dense deposit disease (DDD) was first reported in 1962 and is characterized by the presence of an extremely electron dense transformation of the glomerular basement membrane. In the early 1970s,  DDD was classified as subtype II of membranoproliferative glomerulonephritis (MPGN). Over the last thirty years, marked differences in etiology and pathogenesis between Type I MPGN and DDD have become apparent. Recent observations have shown that DDD can be seen with markedly different light microscopy appearances with apparently different prognostic significance.

Type II MPGN is characterized by a dense homogenous deposition along the glomerular basement membrane and in the mesangium. Deposits can be different, in dimension and diffusion, even among the glomeruli of a given biopsy. When deposition is mild, ultrastructural examination is fundamental for diagnosis.

 

 

The glomerular basement membrane is diffusely thickened by dense homogenous deposits, very evident at higher magnification.

 

 

The same dense deposits frequently involve the Bowman’s capsule.

 

 

The tubular basement membranes may contain the deposits as well.

 

 

Type II MPGN shows variable histological features. The most common form is similar to the classic form of Type I MPGN, with intense mesangial proliferation and mesangial matrix increase.

 

 

Also in Type II MPGN there are cases of focal and segmental membranoproliferative lesions.

 

 

In some cases only minimal lesions can be observed and differential diagnosis has to be made from minimal change disease, stage I MGN and some cases of IgA GN.

 

 

Although at higher magnification it is possible to recognize the segmental thickening of the capillary wall, an accurate diagnosis is only possible by electron microscopy examination.

 

 

Segmental extracapillary proliferation can be present.

 

 

C3 immune deposits are intense along the glomerular basement membrane and in the mesangium. This peculiar immunohistological pattern has been variably described as linear, pseudolinear, ribbon-like, granular or nodular. The deposits are also found on the Bowman’s capsule and on some tubular basement membranes.

 

 

Electron microscopy is essential for diagnosis and shows the linear ribbon-like deposits in the glomerular basement membrane (x 1700).

 

 

Ribbon-like deposits can be of various thickness (x 6000 - x 6000).

 

 

The Bowman’s capsule and the tubular basement membrane show the same electrondense deposition. (x 3600)

 

 

QUESTIONS

 

REFERENCES
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