[A case of mixed connective tissue disease with microscopic polyarteritis nodosa associated with perinuclear-antineutrophil cytoplasmic antibody and anti-glomerular basement membrane].

A 46-year-old female was admitted to our hospital due to general fatigue, systemic edema and dyspnea with history of systemic sclerosis (SSc). The patient was diagnosed as mixed connective tissue disease (MCTD) based on Raynaud phenomenon, a high anti-RNP antibody level and clinical symptoms and laboratory findings suggesting SSc, dermatomyositis (DM) and systemic lupus erythematosus (SLE). After the admission, both alveolar hemorrhage and a rapidly progressive glomerulonephritis (RPGN) also developed and laboratory findings showed a positive remark of myeloperoxydase-antineutrophil cytoplasmic antibody (MPO-ANCA) and anti-glomerular basement membrane (GBM) antibody. She was therefore re-diagnosed as microscopic polyarteritis nodosa (microscopic PAN) combined with MCTD and treatment with high dose prednisolone and steroid pulse therapy dramatically improved general conditions and lung symptoms, but maintenance dialysis was persistent because of irreversible renal failure. However, 3 months after the admission, she died of acute exacerbation of interstitial pneumonitis that was unresponsive to steroid pulse therapy. Autopsy revealed interstitial pneumonitis with alveolar hemorrhage and crescentic glomerulonephritis (CrGN), in which immunofluorescent microscopy showed no deposition in agreement with pauciimmune type. The histological findings supported the diagnosis; primary microscopic PAN combined with MCTD, which is a quite rare case, to our knowledge. Furthermore, co-existence of MPO ANCA and anti-GBM antibody, clinical and histological findings of the case also lead us to reconsider the relevance of these antibodies to pathogenesis and/or categories of microscopic PAN and Goodpasture's syndrome.