The use of muscle biopsy in the diagnosis of systemic vasculitis affecting small to medium-sized vessels: a prospective evaluation in Japan.

OBJECTIVES: The aim of this study was to assess the use of muscle biopsy for histopathological confirmation of small vessel vasculitis (SVV) or medium vessel vasculitis (MVV).

METHOD: Muscle biopsies were performed for all consecutive cases of suspected SVV or MVV seen at Tokyo Metropolitan Tama Medical Centre between February 2012 and May 2014 except those for which a skin or renal biopsy was indicated.

RESULTS: Forty-nine patients underwent muscle biopsies. All patients were followed for a minimum of 6 months. Diagnosis of SVV or MVV was made in 35 patients. An unrelated condition was diagnosed in 11 patients and no diagnoses were made in three patients. Of the 35 patients in whom SVV or MVV was diagnosed, positive muscle biopsies were obtained in 20 patients [15 microscopic polyangiitis (MPA), three polyarteritis nodosa (PAN), and two eosinophilic granulomatosis with polyangiitis (EGPA)], while other findings led to the same diagnosis in 15 (seven MPA, four GPA, three PAN, and one rheumatoid vasculitis). The sensitivity of the muscle biopsy was 57% [20/35; 95% confidence interval (CI) 50-57]. Of 13 patients presenting with peripheral neuropathy, the muscle biopsy demonstrated vasculitis in nine patients, with 75% sensitivity (9/12; 95% CI 69-75). There were no complications in the procedure apart from delayed wound healing in one patient.

CONCLUSIONS: Muscle biopsy is a safe method that offers a high diagnostic yield for SVV or MVV, especially in patients with vasculitic neuropathy.