How are the inflammatory myopathies diagnosed?

Diagnosis is based on the patient’s medical history, results of a physical exam and tests of muscle strength, and blood samples that show elevated levels of various muscle enzymes and autoantibodies.  Diagnostic tools include electromyography to record the electrical activity that controls muscles during contraction and at rest, and ultrasound and magnetic resonance imaging to reveal abnormal muscle and evaluate muscle disease.  A muscle biopsy can be examined by microscopy for signs of chronic inflammation, muscle fiber death, vascular deformities, or the changes specific to the diagnosis of IBM.  A skin biopsy can show changes in the skin layer in patients with dermatomyositis.