Inflammatory leucocyte infiltrates are associated with recovery in biopsy-proven acute interstitial nephritis: a 20-year registry-based case series

BACKGROUND: Acute interstitial nephritis (AIN) is a renal injury causing renal function deterioration and requiring renal replacement therapy (RRT) in a substantial number of cases. Therapy is based on withdrawal of suspicious causative drugs or the underlying diseases and/or steroid application if renal function is not restored after cessation of the underlying condition. Hard clinical evidence for augmenting steroid therapy is not available. METHODS: We reviewed the course and diagnosis for >20 years among all 1126 biopsied samples of our tertiary renal centre. RESULTS: 49 (4.4%) were diagnosed with primary AIN, corresponding to an annual incidence of 1/100 000 population; 17 out of 49 biopsy-proven AIN patients required short-term or long-term (n = 5) RRT. According to a combined outcome criterion of coming off dialysis and/or reaching serum creatinine <200 µmol/L, 19 patients reached recovery whereas 20 did not. Among 39 patients with a comprehensive clinical and histopathological data set, presence of cortical scars, AIN histological activity (acute leucocyte infiltrates) and proteinuria were baseline parameters discriminating significantly between groups with or without recovery. No associations with the presence of specific drugs were found. Therapeutic use of steroids was associated with a lower probability of recovery (P = 0.008), presumably due to inclusion bias. CONCLUSIONS: Following our basic finding of the importance of histopathological parameters of acuity associated with recovery, we argue for the inauguration of grading measures to characterize this issue quantitatively and make it usable for future controlled investigations. Finally, we provide a suggestion for a therapeutic algorithm in the management of AIN.