Diseases > Polymyositis (PM)
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Polymyositis (PM) and Dermatomyositis (DM) are diseases that affect muscles. These diseases cause inflammation in the muscles. This causes weakness of the muscle. It is important to know that the muscles affected are not painful. They are weak but not painful. The biggest difference between PM and DM is a rash. The rash happens with dermatomyositis (DM).
To keep things easier we’ll discuss both polymyositis and dermatomyositis together. We’ll refer to both PM and DM as simply myositis. In fact they are both types of inflammatory myopathies.