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Tests and diagnosis
By Mayo Clinic staffDiagnosis of polymyositis isn't always easy and can be a lengthy process. Even though the attempt to diagnose your condition may be frustrating, remember that an accurate diagnosis is necessary to receive appropriate treatment.
In addition to a thorough physical exam, your doctor will likely use other tests to confirm a diagnosis of polymyositis.
Imaging tests
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Magnetic resonance imaging (MRI). A scanner creates cross-sectional images of your muscles from data generated by a powerful magnetic field and radio waves.
As MRI has become more sensitive, doctors have been using it more to diagnose inflammatory myopathies. MRI can detect active inflammation in your muscles, fibrosis and calcification. Its high sensitivity can detect subtle muscle inflammation and swelling early in the disease. A benefit of MRI is that it can look at large amounts of muscle to look for patterns or patches of muscle weakness, instead of taking a small sample from a single muscle, for example.
Muscle tests
- Electromyography. A doctor with specialized training inserts a thin needle electrode through the skin into the muscle to be tested. 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.
- Muscle biopsy. A small piece of muscle tissue is removed surgically for laboratory analysis. A muscle biopsy may reveal abnormalities in your muscles, such as inflammation, damage or infection. The tissue sample can also be examined for the presence of abnormal proteins and checked for enzyme deficiencies. In polymyositis, a muscle biopsy typically shows inflammation, dead muscle cells (necrosis), and degeneration and regeneration of muscle fibers.
Blood tests
- Blood analysis. A blood test will let your doctor know if you have elevated levels of muscle enzymes, such as creatine kinase (CK) and aldolase. Increased CK and aldolase levels 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.
- NINDS polymyositis information page. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/polymyositis/polymyositis.htm. Accessed May 21, 2009.
- Baer A. Advances in the therapy of idiopathic inflammatory myopathies. Current Opinion in Rheumatology. 2006;18:236.
- Dalakas MC. Inflammatory disorders of muscle: Progress in polymyositis, dermatomyositis and inclusion body myositis. Current Opinion in Neurology. 2004;17:561.
- Miller ML. Clinical manifestations and diagnosis of adult dermatomyositis and polymyositis. http://www.uptodate.com/home/index.html. Accessed May 8, 2009.
- Di Martino SJ, et al. Newer therapeutic approaches: Inflammatory muscle disorders. Rheumatic Disease Clinics of North America. 2006;32:121.
- Koski CL, et al. Intravenous immunoglobulin use for neurologic diseases. Journal of Infusion Nursing. 2006;29:S21.
- Amato AA, et al. Treatment of idiopathic inflammatory myopathies. Current Opinion in Neurology. 2003;16:569.
- Oddis CV. Current approach to the treatment of polymyositis and dermatomyositis. Current Opinion in Rheumatology. 2000;12:492.
- Walker UA. Imaging tools for the clinical assessment of idiopathic inflammatory myositis. Current Opinion in Rheumatology. 2008;20:656.
- Miller ML, et al. Initial treatment of dermatomyositis and polymyositis in adults. http://www.uptodate.com/home/index.html. Accessed May 8, 2009.
- Miller ML, et al. Treatment of recurrent and resistant polymyositis and dermatomyositis. http://www.uptodate.com/home/index.html. Accessed June 15, 2009.
