Clinical characteristics of patients with myalgia as the initial manifestation of small and medium-sized vasculitis: a retrospective study

Myalgia is a common symptom in small and medium-sized systemic vasculitis, sometimes occurring as the initial or only clinical manifestation of vasculitis. This study investigated the clinical features and diagnostic process in patients presenting with myalgia as the initial symptom of anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) or polyarteritis nodosa (PAN). We included 93 patients diagnosed with AAV or PAN by retrospectively reviewing their clinical records at the initial diagnosis. Clinical findings and diagnostic methods were assessed in patients with myalgia. Of 93 patients, myalgia was observed in 21 (22.6%) patients, with diagnostic classifications of microscopic polyangiitis (MPA) in 12 (52.4%), granulomatosis with polyangiitis in 2 (9.5%), eosinophilic granulomatosis with polyangiitis in 2 (9.5%), and PAN in 5 (23.8%). Myalgia was present in the lower extremities of all patients; more than 80% of patients had pain in the calf muscle. In 10 patients with myalgia, including 7 with MPA and 3 with PAN, muscle biopsy was performed because myalgia was the main symptom and no other impaired organs were suitable for biopsy. Consequently, 8 patients had necrotizing vasculitis, leading to MPA or PAN diagnosis, although muscle pathology was not evaluated in patients without myalgia. Muscle magnetic resonance imaging was useful in determining the biopsy site. Myalgia, especially in the lower limbs, may be an initial clinical sign of vasculitis, particularly in MPA or PAN patients. Moreover, the histological evidence of muscular vasculitis can contribute to a definite diagnosis especially in patients presenting with myalgia as an early symptom of AAV or PAN.