• Marc-Etienne Parent, Sandrine Larue, and Benjamin Ellezam.
• Department of Internal Medicine, Université de Sherbrooke, 3001 12e Avenue, Fleurimont, QC J1H 5N4, Canada. Marc-Etienne.Parent@USherbrooke.ca.
• Bmc Musculoskel Dis. 2014 Nov 21; 15: 388.

BackgroundEosinophilic granulomatosis with polyangiitis is a complex multisystemic syndrome with heterogeneous presentation. Most often, there is a clinical history of asthma or other atopic conditions, and current presentation generally includes signs of cutaneous or pulmonary involvement. Very few reports described myalgia or weakness as the chief complaint. Of these, only a few included muscle biopsy evaluation and none showed convincing evidence of primary myositis. We believe this report is the first to demonstrate true myositis in the setting of early eosinophilic granulomatosis with polyangiitis.Case PresentationThis report describes a 74 year old Caucasian man, with no known allergies, presenting severe myalgia, muscle weakness, jaw claudication, and fever. Blood work showed marked eosinophilia and high creatine kinase levels. Biceps brachialis muscle biopsy revealed eosinophilic necrotizing vasculitis and true myositis with myophagocytosis of non-necrotic fibers and strong sarcolemmal MHC-1 overexpression by immunohistochemistry. This patient was successfully treated with prednisone and azathioprine.ConclusionOur finding of true myositis in a case of eosinophilic granulomatosis with polyangiitis suggests that primary auto-immunity against muscle fibers, distinct from the secondary effects of vasculitis, can occur in this entity and may represent an overlap syndrome. Early recognition of eosinophilic granulomatosis with polyangiitis in patients presenting with myositis may provide an opportunity to treat the vasculitis before onset of severe multisystemic disease. We recommend the use of muscle biopsy with immunohistochemistry for MHC-1 to confirm the diagnosis of myositis in the setting of eosinophilic granulomatosis with polyangiitis.

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