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| Focal eosinophilic myositisa | Eosinophilic polymyositisb | Eosinophilic perimyositisc |
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Major | (1) Pain and calf swelling (other muscles can be affected) (2) Deep eosinophilic infiltration with muscle fiber invasion and necrosis on muscle biopsy | (1) Proximal weakness affecting limb girdle muscles (may be severe) (2) Widespread deep infiltration of eosinophil into muscles, with eosinophilic cuffing, on histology. Myonecrosis and endomysium inflammation usually +ve. If −ve deposition of MBP should be demonstrated by immunostain | (1) Myalgia, proximal mild weakness (2) Eosinophilic infiltrate confined to fascia and superficial perimysium, absence of myofiber necrosis |
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Minor | (1) ↑ CPK and aldolase (2) MRI or EMG evidence of focal myositis (3) Absence of systemic illness (4) Eosinophilia >0.5 × 109/L | (1) ↑ CPK and aldolase (2) Eosinophilia >0.5 × 109/L (3) Systemic illness with frequent cardiac involvement (4) Steroids are needed | (1) Absence of systemic manifestations (2) Normal CK and aldolase levels (3) Eosinophilia >0.5 × 109/L |
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Exclude | DVT, cellulitis, parasitic infection | HES, cell T clonality, DM, vasculitis (CSS), drugs, calpainopathy, parasitic infections | Toxic oil syndrome, myalgia-eosinophilia, exposure to inorganic or organic substances |
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Treatment | No steroid treatment required. Symptoms resolve spontaneously | Prednisone 0.5–1 mg/kg/day is the treatment of choice | Rarely requires steroid treatment for symptom resolution |
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