Azathioprine-induced interstitial nephritis in an anti-neutrophil cytoplasmic antibody (ANCA) myeloperoxidase (MPO) vasculitis patient

Abstract

Azathioprine (AZA) is used in a wide array of autoimmune diseases, still corresponding to the main-stay maintenance therapy in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides.Although generally well-tolerated, several side effects are recognized. We report the case of a 50-year-old Caucasian man with kidney-limited ANCA myeloperoxidase (MPO) vasculitis who presented withgeneral malaise, fever, worsening renal function, and elevated inflammatory markers 2 weeks afterthe initiation of therapy with oral AZA. Although a disease relapse was suspected, renal biopsy re-vealed an eosinophilic infiltrate, suggestive of acute interstitial nephritis. After suspension of AZA, asustained improvement of renal function and normalization of inflammatory markers was observed.A diagnosis of allergic interstitial nephritis secondary to AZA was established, corresponding to thefirst biopsy-proven case described in an ANCA MPO vasculitis patient. Although rare, renal toxicityof AZA must be present in the clinician ́s mind, avoiding the straightforward assumption of diseaserelapse in the case of worsening renal function.