MPO-ANCA-positive conversion and microscopic polyangiitis development in idiopathic interstitial pneumonia: a case report

Shingo Nakayama, Akari Endo, Takuo Hirose, Keiji Matsumoto, Ayaka Kamada, Hiroki Ito, Hideaki Hashimoto, Katsuya Ishiyama, Ikuko Oba-Yabana, Tomoyoshi Kimura, Hannah Nakamura, Masahito Ebina, Takefumi Mori

Research output: Contribution to journalArticlepeer-review


Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a systemic autoimmune disease characterized by necrotizing inflammation of the small blood vessels. ANCA-associated vasculitis is subclassified into three variants: granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, and microscopic polyangiitis (MPA). Myeloperoxidase (MPO) ANCA is a marker antibody for MPA. Interstitial pneumonia (IP) is occasionally complicated with MPA. However, only a few cases of idiopathic IP develop MPO-ANCA-positive conversion and MPA. Therefore, we present a case of a 70-year-old Japanese man with idiopathic IP who developed MPO-ANCA-positive conversion and MPA. We performed renal biopsy, which revealed pauci-immune crescentic glomerulonephritis. The patient was treated with intravenous methylprednisolone pulse therapy and oral prednisone, and the patient's laboratory data gradually improved with steroid therapy. The association between the production of MPO-ANCA and IP remains unclear, and the present case suggests that IP plays a role in inducing MPO-ANCA production. Patients with idiopathic IP should be followed-up carefully for an examination of increased MPO-ANCA levels and MPA development. In addition, early gastric cancer was detected during upper gastrointestinal endoscopy in our case, and it could also be important not to miss malignancy in patients with ANCA-associated vasculitis.

Original languageEnglish
Pages (from-to)39-44
Number of pages6
JournalCEN case reports
Issue number1
Publication statusPublished - 2023 Feb 1


  • Idiopathic interstitial pneumonia
  • MPO-ANCA-positive conversion
  • Malignancy
  • Microscopic polyangiitis


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