Eosinophilia-associated myopathies are clinically and pathologically 
heterogeneous conditions characterized by the presence of peripheral and/or 
muscle eosinophilia. There are at least three distinct subtypes: focal 
eosinophilic myositis, eosinophilic polymyositis, and eosinophilic perimyositis. 
Infiltrating eosinophils are not always identified in conventional muscle 
histologic examination, but the eosinophil major basic protein, whose 
extracellular diffusion is considered a hallmark of eosinophilic cytotoxicity, 
is usually detected by immunostaining in muscle biopsy. Whereas focal 
eosinophilic myositis seems to be a benign and isolated condition, and 
perimyositis is usually related with the inflammatory infiltrate due to 
fasciitis, eosinophilic polymyositis can be associated with muscular dystrophy 
or be a feature of multiorgan hypereosinophilic syndrome. Muscle biopsy remains 
the cornerstone for the diagnosis. Parasitic infections, connective tissue 
disorders, hematologic and non-hematologic malignancies, drugs, and toxic 
substances are the main etiologic agents of eosinophilia-associated myopathy. 
However, in some cases, no known etiologic factor is identified, and these are 
considered idiopathic. Glucocorticoids are the mainstay therapy in idiopathic 
forms. Imatinib and mepolizumab, a humanized anti-interleukin 5 monoclonal 
antibody, may be useful in patients with eosinophilic myositis as part of a 
hypereosinophilic syndrome.