AP-VAS 2012 case report: MPO-ANCA-negative relapse of MPO-ANCA-associated vasculitis.

A 79-year-old female was admitted to our hospital with fever, proteinuria, hematuria, high levels of C-reactive protein (CRP), and high titer of myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA). Our diagnosis was microscopic polyangiitis (MPA) and she was treated with steroid pulse therapy. Clinical remission was induced; however, the disease relapsed with saddle nose and necrotizing vasculitis of the nasal cavity mucosa 1 year later. Although there was no elevation of the MPO-ANCA titer, we diagnosed the patient with relapse of MPO-ANCA-positive granulomatosis with polyangiitis (GPA). Remission was induced again with steroids and azathioprine. It has been reported that the number of MPO-ANCA-positive patients in Asian countries is relatively higher than in Western countries. We checked 29 GPA patients in our hospital and 9 patients (31.0 %) were MPO-ANCA-positive. In addition, it is not rare that an ANCA-associated vasculitis (AAV) patient who has been in remission with negative ANCA relapses without any elevation of ANCA titer. We checked the transition of ANCA titer of 24 AAV patients in our hospital who relapsed and 6 patients (25 %) relapsed without any elevation of ANCA titer. We should be careful for a relapse, even if the ANCA titer remains negative. It is also possible that ANCA had been changed so as not to be detected by the same enzyme-linked immunosorbent assay (ELISA) kit. Thus, it is also important to change the detection system if clinical symptoms are worsened while ANCA is still negative.