Muscle biopsy for the diagnosis of ANCA-associated vasculitis: A case series and literature review

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is diagnosed on the basis of a combination of clinical symptoms, imaging findings, and histological findings. In general, skin, kidney, upper airway and lower airway tissues are selected as biopsy targets. However, some patients present with few abnormalities in these major organs. Herein, we report three patients with AAV who presented with myalgia as a main symptom, with high C-reactive protein levels and a positive myeloperoxidase-ANCA test without elevated serum creatine kinase levels. All the patients underwent muscle magnetic resonance imaging and muscle biopsy (MB) to diagnose AAV. We also investigated peer-reviewed cases of AAV that were diagnosed by MB to confirm the efficacy of MB for AAV. Several retrospective studies have reported MB sensitivity to AAV and its predictors. We argue that an MB from the area where myalgia, muscle weakness, and abnormal MRI signals are present is useful for the diagnosis of AAV.