Signs and Symptoms of Myositis

The hallmark feature of myositis is muscle weakness with an onset that is often insidious. Patients complain of ‘proximal’ weakness with difficulty holding their arms above their head or getting up from a chair or walking up steps. DM is characterized by any number of rashes located on the face, hands, elbows, knees or scalp but rashes can become generalized as well. Many other signs and symptoms occur such as fatigue, fever, Raynaud phenomenon, difficulty swallowing and joint pain, but pulmonary involvement is an important and serious feature commonly seen in patients with PM and DM. Such patients complain of dyspnea and may develop interstitial lung disease (ILD) alone or in combination with pulmonary hypertension.


Myositis can be difficult to diagnose and there are many mimics of the IIM including drug-induced myopathy, thyroid problems, various neurologic conditions or even forms of muscular dystrophy.
Tests that are helpful in making the diagnosis of myositis include:

  • Blood tests: Any one of several muscle enzymes may be elevated including the serum creatine kinase (CK), transaminases (AST and ALT), lactate dehydrogenase (LDH) and aldolase. Other inflammatory tests may be elevated and there are a number of autoantibodies known to be associated with myositis.
  • Electromyography (EMG): Characteristic findings on EMG are seen in patients with myositis and these tests are generally performed under the direction of a neurologist or physiatrist.
  • MRI: Magnetic resonance imaging may be used to aid in the diagnosis of some patients with myositis – particularly children, as EMG can be painful.
  • Muscle Biopsy: This is often considered the gold standard in patients with myositis and is essential in most cases of PM due to the many mimics of this subset of IIM. However, it is also frequently performed in DM as the skin rash may be subtle and it always helps to make a definitive diagnosis of myositis to confirm the clinical suspicion.

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