Muscle biopsy in anti-neutrophil cytoplasmic antibody-associated vasculitis: diagnostic yield depends on anti-neutrophil cytoplasmic antibody type, sex and neutrophil count.

Objectives: This study aimed to examine the sensitivity of muscle biopsy (MB) in ANCA-associated vasculitis (AAV), identify factors predicting MB positivity and assess the prognostic value of a positive MB.

Methods: We conducted a single-centre retrospective study of AAV with an MB performed at diagnosis. AAV classification [granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis (EGPA)] followed the European Medicines Agency algorithm.