A Narrative Review of the Diagnostic Role of Muscle Biopsy in Small- to Medium-Vessel Vasculitis: Consideration of Imaging-Guided Procedures.

Muscle biopsy (MB) remains an important diagnostic option in small- to medium-vessel vasculitis, particularly when other tissue biopsies are non-diagnostic. This narrative review aimed to clarify the diagnostic role of MB, summarize key histopathological features, and evaluate the clinical utility of imaging-guided procedures. A structured literature search of Medline/PubMed (2000-2025) identified 10 relevant studies for synthesis. Available evidence indicates that skeletal muscle is a valuable tissue for detecting vasculitic lesions, even in the absence of myalgia or creatine kinase elevation. Reported diagnostic yields vary across studies, reflecting differences in patient selection, biopsy techniques, and imaging use. Higher yields have been reported in imaging-guided procedures, particularly MRI-guided biopsy. However, evidence is largely derived from small retrospective and heterogeneous cohorts. Adequate sampling, including epimysial and perimysial tissue with appropriate staining, is essential to improve diagnostic reliability. In clinical practice, MB should be considered when suspicion of vasculitis persists despite non-diagnostic initial investigations. MRI may assist in identifying target biopsy sites and reducing sampling error. Overall, MB demonstrates diagnostic value in clinical practice, although results vary considerably and evidence remains heterogeneous.