The successful treatment of microscopic polyangiitis associated with non-tuberculous mycobacterial-pulmonary disease.

While the incidence and prevalence of non-tuberculous mycobacterial-pulmonary disease (NTM-PD) are increasing and microscopic polyangiitis (MPA) is common in East Asian countries, case reports of MPA associated with NTM-PD are limited. A 72-year-old male receiving treatment for NTM-PD with antibiotics was referred to our hospital with fever and arthralgia that developed a few months previously. A blood test revealed the presence of the myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA) and renal impairment. Based on a pathological examination of renal tissue, which showed crescentic glomerulonephritis, the patient was diagnosed with MPA. Due to acute kidney injury and strongly positive MPO-ANCA, pulse steroid therapy was initiated followed by intravenous rituximab (RTX). The patient also received plasmapheresis (14 sessions). Renal dysfunction was reversed. MPA associated with NTM-PD is extremely rare and, thus, there is currently no established treatment. Our patient was diagnosed with MPA based on the findings of renal biopsy while receiving treatment for NTM-PD. RTX and plasmapheresis combined with systemic glucocorticoid therapy were initiated before these clinical conditions had fully recovered. Although MPA secondary to NTM-PD may be more refractory to treatment than primary MPA in the presence of a very low interferon-gamma (IFN-γ) level, this case was successfully treated with steroids, RTX, and plasmapheresis.