Minimal LM canges

• Minimal Light Microscopic Alterations– Minimal change disease– Thin glomerular basement membrane disease

(TBMD)– Lupus nephritis, class I– Immunoglobulin A (IgA) nephropathy, with no

lesion by light microscopy

Minimal Change Disease• Histopathology: • LM usually discloses no significant abnormalities• GBM- unremarkable thickness and texture• Mesangium +/- mild expansion• Podocytes +/- slightly prominent but no proliferative changes

(pseudocrescents) • Proximal tubules may contain prominent protein reabsorption

granules• The interstitium is usually delicate; foamy macrophages may be

seen on rare occasions• Acute interstitial nephritis may be seen in association with

drug-induced (particularly NSAID-induced) minimal change disease• Interstitial fibrosis and tubular atrophy may be seen in elderly

patients with comorbid states

• Immunofluorescence: • +/- fine granular reactivity for IgG within the podocyte cytoplasm (dusting). • No immune deposits present along the peripheral capillary loops or in the

mesangium

• Electron microscopy: • Visceral epithelial cells: Hallmark- diffuse effacement of visceral epithelial cell

foot processes in the absence of electron-dense deposits. • Other degenerative changes of visceral epithelial cells: microvillous degeneration,

vacuolization of the cytoplasm, increased number of lysosomes and other cytoplasmic organelles

• GBM: Usually unremarkable• Glomerular endothelial cells: Usually unremarkable and do not contain

tubuloreticular structures• Mesangium: Normal cell elements and an extracellular matrix without

electron-dense deposits

IgA

• Histopathology: • Glomeruli are normal, or they show minimal

mesangial expansion• The glomerular basement membranes are of

unremarkable thickness and texture• The mesangium may be minimally expanded, but is

normocellular• The tubulointerstitium is usually unremarkable• This form of IgA is quite common and can be

detected incidentally on renal biopsy, superimposed to any other renal disease

• Immunofluorescence: • Dominant reactivity for IgA in the mesangium; C3 may be equally or less

reactive. There is usually stronger reactivity for lambda than for kappa light chains in the mesangial deposits

• Electron microscopy: • Visceral epithelial cells: Unremarkable, with well-preserved foot

processes• Glomerular basement membranes: May be thin; there is higher

incidence of thin glomerular basement membrane disease in IgA nephropathy than in any other glomerular disease.

• Glomerular endothelial cells: Usually unremarkable and tubuloreticular structures are not seen.

• Mesangium: Shows normal cell elements and an extracellular matrix with scattered small fine granular electron-dense deposits

Class I lupus nephritis

• Histopathology: • Light microscopic examination usually

discloses no significant abnormalities• The glomerular basement membranes are

of unremarkable thickness and texture• The mesangium may be mildly expanded,

but is normocellular• The tubulointerstitium is usually

unremarkable

• Immunofluorescence: • 'Full house' reactivity

• Electron microscopy: • Visceral epithelial cells: Unremarkable and foot processes are

well preserved• Glomerular basement membranes: Normal appearance and

texture• Glomerular endothelial cells: May contain tubuloreticular

structures• Mesangium: Shows normal cell elements and an extracellular

matrix with scattered fine granula electron-dense deposits

Thin Glomerular BMD• Histopathology: • The capillary loops are of normal contour and

may appear delicate• Normocellular mesangium• The tubules and interstitium are usually

unremarkable; foamy macrophages may be seen on rare occasions in the interstitium

• More pronounced interstitial fibrosis and tubular atrophy may be seen in elderly patients with comorbid states

• Electron microscopy: • Visceral epithelial cells:• The visceral epithelial cells and their foot processes are well

preserved.• Glomerular basement membranes: Morphometric

measurements disclose diffuse thinning, with the mean thickness below the lower normal limit of 264 nm. Electron-dense deposits are not seen along the capillary loops

• Glomerular endothelial cells: Unremarkable and do not contain tubuloreticular structures

• Mesangium: Normal cell elements and an extracellular matrix without electron-dense deposits