Application of Electrical Impedance Myography (EIM) as a Potential Biomarker of Idiopathic Inflammatory Myopathies

Inclusion Criteria: * duration of weakness \>12 months. * ages 18 to 80 years old. * serum CK level no greater than 15 times the upper limit of normal. * quadriceps weakness \>hip flexor weakness and/or finger flexor weakness \>shoulder abduction weakness. * one or more of the following pathological findings: * endomysial inflammatory infiltrate. * rimmed vacuoles. * protein accumulation or 15-18 mm filaments. DM/PM inclusion criteria: * ages 18 to 80 * Symmetric proximal weakness * Elevated CK * EMG suggestive of myopathy with evidence of muscle membrane irritation * Muscle biopsy suggestive of inflammatory myositis (degeneration, regeneration, necrosis, and interstitial mononuclear infiltrates) * Typical skin rashes of DM (Heliotrope rash or Gottron sign) Key inclusion criteria for the control group: * no active neuromuscular disorders or known history of neuromuscular disorders. * no sign or symptoms of muscle weakness. * no family history of muscular dystrophies or ALS. * ages 18 to 80 Exclusion Criteria: * Patients with decompensated congestive heart failure * Patients with chronic kidney disease on hemodialysis * Patients with active cancer on chemotherapy or radiotherapy * Patients with severe disease who are already wheel chair bound