[Clinico-pathological and follow-up analysis of 5 skeletal muscle single-organ vasculitis cases].

Objectives: To delineate clinico-pathological features, treatment and outcome of skeletal muscle single-organ vasculitis (SM-SOV). Methods: The clinico-pathological characteristic of SM-SOV cases treated over 3 years in China-Japan Friendship Hospital were retrospectively analyzed and the data were compared with the cases from the literature. Results: Five patients (2 women and 3 men) with a median age of 36 years were included in this study. The main clinical manifestations were lower limb myalgia (5/5) and fever (1/5). The most frequent laboratory findings included high erythrocyte sedimentation rate (5/5), high C reactive protein (5/5) and leukocytosis (1/5). No elevated creatine kinase (CK) was found in these cases. Four patients received electromyogram examination and none of them showed myogenic injury. On MRI, hyperintense signals in T2 weighted image (T2WI) and/or short TI inversion recovery (STIR) and normal unenhanced T1 weighted image (T1WI) of one or several leg muscles was founded in all 5 patients. All muscle specimens showed nongranulomatous vasculitis without myonecrosis affecting small sized artery (5/5) in perimysia (75.0%, 3/4) or both perimysia and fascia (25.0%, 1/4). Corticosteroids (5/5) and immunosuppressants (5/5) were the main agents prescribed. With a median follow-up of 24 months, sustained remission was observed in 3 patients, relapses occurred in 2 patients. Conclusion: SM-SOV should be considered for patients with lower limb myalgia, high inflammatory markers and normal/low CK level. The diagnosis of SM-SOV should be applied when there are both histologic evidence of vasculitis and a minimum of 6 months of follow-up surveillance without evidences suggesting extra-muscular involvement. Corticosteroid combined with immunosuppressant is effective.