Minimal change disease and focal segmental glomerulosclerosis.

Minimal change disease (MCD) accounts for greater than 90% of cases of nephrotic syndrome in children. In adults, MCD accounts for 10–15% of nephrotic syndrome. FSGS is increasing in incidence in adults and children, and in the USA, in adults, is now the most common cause of nephrotic syndrome w1,2x. MCD shows normal glomeruli by light microscopy. Associated acute interstitial nephritis suggests a druginduced hypersensitivity reaction, frequently due to NSAIDs. In FSGS, sclerosis involves some, but not all glomeruli (focal), and the sclerosis affects a portion, but not the entire, glomerular tuft (segmental). The sclerotic process is defined by glomerular capillary collapse with increase in matrix. This segmental scarring contrasts the global glomerulosclerosis, which occurs non-specifically with aging. Arteriolar hyalinosis may occur with hypertensive injury, and should not be taken as evidence of a sclerotic lesion. Immunofluorescence studies are typically negative in MCD. In FSGS, immunofluorescence may show non-specific entrapment of IgM and C3 in sclerotic areas or areas where mesangial matrix is increased. Electron microscopy shows foot process effacement, vacuolization, and microvillous transformation of epithelial cells in both MCD and FSGS. In MCD, foot process effacement is typically extensive. Foot process effacement is often not complete in FSGS.