Localized eosinophilic myositis of the masseter muscle associated with actinomycosis

A case of eosinophilic myositis of the masseter associated with pseudotumor and trismus is presented. Extensive eosinophilic infiltrates of the masseter are rarely observed in the absence of parasitic infection or the hypereosinophilic syndrome. This case is reported because of the rarity of the phenomenon and its importance to the surgeon from the standpoint of differential diagnosis and treatment. The pathogenesis of the condition and its relation to other lesions of muscle associated with eosinophilic infiltration are discussed.