Interstitial Nephritis

Interstitial nephritis

Interstitial nephritis can be classified as acute, chronic, suppurative or nonsuppurative. Fibrosis occurs as well as tubular degeneration and atrophy. Infectious, toxic, immunologic and chemical aetiologies have been implicated.

Nonsuppurative

• Nonsuppurative interstitial nephritis can be either acute, subacute or chronic.

Gross pathology

• In acute cases, the kidneys are often enlarged and have pale cortices with a streaked appearance.
• In chronic cases, shrinkage of the kidney as well as extensive fibrosis and capsular adhesions occurs.

Histopathology

• Presence of inflammatory cells in the interstitium.
• Degenerative changes of the tubular epithelium.
• Presences of fibrous tissue due to repair attempts by the kidney.

Examples

• 'White spot' kidney of calves and Leptospira canicola infection are both examples of nonsuppurative interstitial nephritis.
  • White spot kidney is common and usually an incidental finding. Kidneys have multiple small, white, slightly raised nodules throughout the cortex. The cause is likely a sequel to previous bacteraemia.
• Leptospira canicola in the dog is also another good example. It localises in the renal capillaries then migrates to the tubules via the interstitium. Necrosis of the tubular epithelium occurs as well as a pronounced interstitial inflammatory reaction. In chronic cases, fibrosis and widespread degenerative changes are seen. The liver, csf and placenta can also be affected.
• If the condition is chronic, marked interstitial fibrosis can be seen as well as degenerative changes in the tubules.

Suppurative

• Suppurative interstitial nephritis follows bacteraemia or embolic septicaemia.
• Can be haematogenous or urogenous in origin.
• If large thrombi lodge in the afferent vessels, infarction may occur.
• Bacteria lodge within the glomeruli and peritubular capillaries.
• Abscesses may occur in the glomeruli or interstitium.
• Examples include Actinobacillus equuli in foals, Erysipelothrix rhusiopathiae in pigs,

Arcanobacterium pyogenes in cattle and Corynebacterium pseudotuberculosis in sheep/goats.