Acute tubulo-interstitial nephritis with positive anti-neutrophil cytoplasmic antibodies.

INTRODUCTION Anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis involving the kidney usually comprises pauci-immune, necrotizing glomerulonephritis with crescents. Mononuclear tubulo-interstitial infiltrates are common in ANCA associated vasculitis, but these have usually been described in conjunction with glomerulitis. Acute tubulo-interstitial nephritis (ATIN) is a common cause of acute kidney injury that is most frequently induced by drugs or infections. Idiopathic ATIN has rarely been reported in association with the presence of a positive ANCA. These two entities seem to share a common immunological basis. CASE REPORT We report a 75 years-old male patient who presented with acute kidney injury and his serum tested positive for p-ANCA by indirect immunofluoresence with a titer of 1/320. Testing by ELISA demonstrated anti-myeloperoxidase (MPO) specificity with a level of 28.8 IU/mL. His kidney biopsy showed features of ATIN with no glomerular involvement. Treatment with corticosteroids led to improvement of his kidney function and serology for ANCA became negative. In this case report ATIN seems to be associated with ANCA positivity, in the absence of other obvious causes for the acute tubulo-interstitial insult. CONCLUSION ATIN can be associated with positive ANCA without features of renal-limited vasculitis or systemic vasculitis. This can occur in the absence of drug exposure. The outcome in our case was favorable with corticosteroid therapy.