4.2.3 Chronic interstitial nephritis

Definition: Prolonged course of acute interstitial nephritis with interstitial fibrosis. Tubulitis is still present.

Diagnosis of chronic interstitial nephritis is often difficult and should only be made when AIN outside the fibrotic zones can be diagnosed in non-atrophic tubules. In these cases eosinophils are rarely present.

Interstitial inflammatory infiltrates in areas of scars, or areas with atrophic tubuli with interstitial fibrosis, should not be considered as interstitial nephritis in the strict sense, rather as a phenomena accompanying the underlying disease. They also do not permit the diagnosis of chronic interstitial nephritis but rather the diagnosis of “chronic (unspecific) tubulo-interstitial damage” should be made.