1.1 Glomerular minimal change

Definition: normal renal tissue by light microscopy. By electron microscopy diffuse and global fusion of the podocyte foot processes.

By light microscopy, renal tissue - glomeruli, vessels and tubulo-interstitial space - are unchanged. In case of any changes in the tubuBy light microscopy renal tissue - glomeruli, vessels and tubulo-interstitial space - are unchanged. In case of any changes in the tubulo-interstitial space, as described under FSGS, the diagnosis of minimal change disease is doubtful.

By electron microscopy the podocytes show a pathognomonic lesion: diffuse and global fusion of the podocytic foot processes (effacement or loss of foot processes). The glomerular structure (basement membrane and mesangium) is unchanged. In some cases, small electron dense deposits along the mesangial basement membrane may be present.

By immunohistology the glomeruli are either completely negative or minute /small deposits of IgM and complement components (C3, C1q, C5-9) in focal and segmental distributions may be found.

The electron dense deposits, the immunoglobulin and complement deposits, as well as the podocytic foot process fusion, may vanish with remission of the nephrotic syndrome.

In addition to the classical picture a few variants are known.

1. Diffuse mesangial hypercellularity: in these cases the mesangium is enlarged due to matrix and cell increase. The peripheral capillary loops are free from inflammatory infiltrates.
2. IgM or C1q nephropathy: in these cases the glomeruli show, by immunohistochemistry, diffuse and global deposits of IgM or C1q.  C1q nephropathy is more often associated with FSGS.
3. MCD and IgA nephropathy: in addition to the typical lesions of MCD, mesangial deposits of IgA are present in a diffuse and global distribution.
4. MCD with acute interstitial nephritis