Anti-neutrophil cytoplasm antibody-negative eosinophilic granulomatous polyangiitis complicated by myositis: a case report.

A 31-year-old woman visited our hospital with swelling and pain in both forearms of 2 months' duration, followed by swelling and pain in both thighs. Her medical history included bronchial asthma at the age of 18 years. After the birth of her first child at 30 years of age, her asthma worsened and was accompanied by abdominal pain and skin rash, with no identifiable cause. Blood testing showed eosinophilia and high muscle enzyme activities, but she was anti-neutrophilic cytoplasmic antibody (ANCA)-negative. Magnetic resonance imaging of her forearms and thighs revealed strong signals on T2-weighted images in the fascia and muscle. Skin-to-muscle en bloc biopsy showed eosinophilic infiltration of muscle and small vessels. She was diagnosed with eosinophilic granulomatosis with polyangiitis (EGPA), complicated by myositis, although EGPA is usually accompanied by ANCA-positivity in approximately half of cases. Treatment was started with prednisolone alone at 0.5 mg/kg/day, and her symptoms and eosinophil count quickly improved. Clinicians should note the possibility of ANCA-negative EGPA complicated by myositis.