A previously healthy 58-year-old man was admitted for muscle pain and weakness [manual muscle testing (MMT) of 4/4 for upper and lower limbs]. We detected elevated levels of inflammatory makers and PR3-anti-neutrophil cytoplasmic antibody (ANCA). Subsequently, the muscle weakness rapidly progressed to an MMT of 2 for all limbs. Magnetic resonance imaging indicated muscle edema, and the creatine kinase (CK) level increased to 29,998 U/L. Methylprednisolone (mPSL) and cyclophosphamide pulse therapy improved the patient symptoms. MMT recovered to 4 for all limbs. A muscle biopsy showed degenerated muscle fibers surrounded by neutrophil-predominant infiltration. In addition, lamina elastic breakdown and fibrinoid necrosis of arterioles were observed. A final diagnosis of microscopic polyangiitis (MPA) limited to the muscles was made.
Keywords: ANCA-associated vasculitis,; PR3-ANCA; organ limited vasculitis.