[A case of MPO-ANCA-related nephritis caused by an anti-tuberculosis drug]

We report a rare case of MPO-ANCA-related nephritis induced by an anti-tuberculosis drug. The patient was a 67-year-old woman who was admitted to our hospital because of proteinuria and renal dysfunction. She had been under treatment with rifampicin (RFP) and ethambutol hydrochloride (EB) for pulmonary nontuberculous mycobacteriosis. Her serum myeloperoxidase (MPO)-ANCA titer was high. Drug-induced MPO-ANCA-related nephritis was suspected. When medication with RFP and EB was terminated, the levels of serum Cr and MPO-ANCA decreased. Renal biopsy examination revealed cell infiltration and fibrosis in the interstitium as well as crescent formations and necrotization of the capillary wall in the glomeruli. These findings were compatible with the diagnosis of ANCA-related nephritis. The standard treatment for ANCA-related glomerular nephritis (GN)is generally steroid pulse therapy, steroid therapy and immunosuppressive drugs. The lymphocyte stimulation test was positive for EB and negative for RFP, suggesting that in our patient EB was the cause of ANCA-related GN. After withdrawal of RFP and EB, the titer of MPO-ANCA decreased and the patient's renal function improved. This outcome is characteristic of drug-induced ANCA-related vasculitis.