Focal Eosinophilic Myositis.

A 72-year-old man presented to the hospital with a 2-day history of rapidly progressive, painful redness, swelling, and warmth of the right thigh (Picture A). His temperature was 38.9℃; the creatine kinase level was 2,139 U/L. Magnetic resonance imaging (Picture B) showed extensive hyperintensity in the muscle (arrows) and intermuscular fascia (arrowheads) on short-tau inversion recovery imaging. These findings suggested necrotizing fasciitis. However, a histological examination (Picture C, Hematoxylin and Eosin staining) revealed endomysial mononuclear cell infiltration with eosinophils (arrows) and muscle fiber necrosis with regeneration (arrowheads). Subsequently, the eosinophil count increased to 2,223 /μL. The patient was diagnosed with focal eosinophilic myositis, a rare and self-limited disease with localized lower limb pain and swelling without other organ involvement (1). The thigh can also be affected (1,2), but the etiologic factors were not identified in the patient. At one-month follow-up after the presentation, the symptoms had spontaneously resolved, with normal laboratory values shown.

Picture.

The authors state that they have no Conflict of Interest (COI).