Diagnosis

If your doctor suspects you have polymyositis, he or she might suggest some of the following tests:

  • Blood tests. A blood test will let your doctor know if you have elevated levels of muscle enzymes, which can indicate muscle damage. A blood test can also detect specific autoantibodies associated with different symptoms of polymyositis, which can help in determining the best medication and treatment.
  • Electromyography. This test involves inserting a thin needle electrode through the skin into the muscle. Electrical activity is measured as you relax or tighten the muscle, and changes in the pattern of electrical activity can confirm a muscle disease. The doctor can determine the distribution of the disease by testing different muscles.
  • Magnetic resonance imaging (MRI). A scanner creates cross-sectional images of your muscles from data generated by a powerful magnetic field and radio waves. Unlike a muscle biopsy, an MRI can assess inflammation over a large area of muscle.
  • Muscle biopsy. During this test, a small piece of muscle tissue is surgically removed for laboratory analysis. Analysis may reveal abnormalities, such as inflammation, damage, certain proteins or enzyme deficiencies.