Granulomatous interstitial nephritis: a rare diagnosis with an overlooked culprit.

Granulomatous interstitial nephritis (GIN) is a rare entity identified in <1% of native kidney biopsies. The most frequent aetiology is drug-related, followed by systemic granulomatous conditions. Among drugs implicated in GIN, antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) are the most frequent. We report the case of a 45-year-old white man referred to a nephrology consult due to chronic kidney disease. He had a history of arterial hypertension with 10 years of evolution, hyperuricaemia, medicated with allopurinol and NSAID abuse for at least 20 years. Urine sediment was blunt, without proteinuria. Renal ultrasound was normal. A kidney biopsy revealed well-defined epithelioid granulomas with glomerular wrinkling and collapse. Infectious and systemic conditions were excluded, favouring the hypothesis of drug-induced GIN, probably related to NSAIDs. Kidney biopsy remains the gold standard for the diagnosis of GIN. Facing a patient with renal failure without significant proteinuria or active sediment, one should look for causes of tubulointerstitial injury.