Background: Acute interstitial nephritis has been known as a complication of mainly streptococcal infection for nearly a century. With the advent of infection control, it became a complication caused by antibiotics and later by other drugs, which might have changed the outcome. To determine risk factors for the development of chronic renal insufficiency, and thus, the transition from acute to chronic interstitial nephritis, we performed a retrospective study of all cases of acute interstitial nephritis found by reviewing 1,068 renal biopsies from 1968 to 1997.
Methods: Patients with permanent and reversible renal insufficiency after acute interstitial nephritis were compared with respect to the causative event, the symptoms, and the clinical and histological findings. Differences between the groups were calculated by applying bi- and multivariate analysis.
Results: Acute interstitial nephritis was found in 6.5% of all biopsies (64 patients with 68 episodes of acute interstitial nephritis); it was infection-induced in 10%, idiopathic in 4%, and drug-induced in 85% of the cases (antibiotics in 13 cases, analgesics in 17, non-steroidal anti-inflammatory drugs (NSAIDs) in 16, diuretics in 5, and various other drugs in 7). Renal insufficiency was reversible in 69% and permanent in 31% (12% partially reversible, 19% irreversible). The infection-induced and idiopathic types of acute interstitial nephritis were always reversible. Drug-related acute interstitial nephritis caused permanent renal insufficiency in 36% with a maximum of 56% in NSAID-induced cases. In drug-induced cases, intake of the suspected drug for more than a month prior to diagnosis caused permanent renal insufficiency in 88% and interstitial granuloma in 31%. Multivariate analysis disclosed the following significant features separating the permanent from the reversible renal insufficiency group: patients in the first group had more tubular atrophy in their histology, more chronic use of mixed analgesics and/or NSAIDs, less oliguria or anuria as an acute symptom, fewer antibiotics as causative agents, more interstitial granuloma, more pronounced interstitial cell infiltration in their histology, and more imaging of renal shrinkage. Renal histology had the highest predictive value.
Conclusion: Today, acute interstitial nephritis is mainly drug-induced. NSAIDs are the most frequent cause of permanent renal insufficiency after acute interstitial nephritis. Clinically, subacute symptoms, a prolonged intake of the suspect drug, and chronic analgesic or NSAID use are related to a more chronic course of interstitial nephritis. In histology, tubular atrophy, interstitial granuloma, and pronounced interstitial cell infiltration indicate chronicity.