An unusual case of acute kidney injury - idiopathic granulomatous tubulointerstitial nephritis.

We present a case which emphasizes the importance of performing a kidney biopsy in each case of acute kidney injury (AKI) of unknown etiology. The unexpected histological diagnosis of granulomatous interstitial nephritis (GIN) is a rare cause of AKI. The main causes of GIN include drugs (NSAIDs, antibiotics), sarcoidosis, and infections (mycobacterial and fungal). In our case, a 68-year-old woman was admitted with AKI, absence of symptoms and unremarkable history, apart from coronary heart disease. Renal biopsy was performed, since history as well as clinical and laboratory data could not define a cause of AKI. A more meticulous clinical and laboratory investigation followed the histological diagnosis in order to rule out sarcoidosis, vasculitis or any other known causes of GIN. Finally the diagnosis was characterized as AKI due to idiopathic GIN. The patient responded well to corticosteroids.