[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.