Use of muscle biopsies for diagnosis of systemic vasculitides.

OBJECTIVE: Few studies have investigated the use of muscle biopsies (MB) for the diagnosis of systemic vasculitides (SV). We aimed to evaluate the diagnostic use of MB in this condition.

METHODS: We reviewed 310 consecutive MB performed in our center between 2000 and 2008 and correlated them with clinical data from the corresponding patients. Thirty-one of the patients, representing a total of 33 MB, were diagnosed with active SV. MB were considered positive when they demonstrated either necrotizing vasculitis or nonnecrotizing vasculitis.

RESULTS: Twenty-two of the 33 MB were positive (sensitivity of 66.7%), with necrotizing vasculitis and nonnecrotizing vasculitis being equally frequent. The SV were antineutrophil cytoplasmic antibody (ANCA)-associated in 22 patients (71%), and ANCA-negative in 9 cases (29%). Neither the type nor the clinical spectrum of the SV was predictive of MB positivity. None of the muscle symptoms (myalgias or biological rhabdomyolysis) were correlated with MB positivity. All the biopsies were performed uneventfully.

CONCLUSION: The feasibility and positive predictive value of MB make it a valuable tool for ruling out a diagnosis of SV. Since no clinical signs could predict its positivity, MB should be considered in all suspected cases of SV. Unlike other biopsies, including kidney biopsy, MB had no prognostic value.