Dermatomyositis and Polymyositis are two similar and rare chronic (long-term) diseases that affect the muscles. They cause inflammation in the muscles that leads to weakness but not usually pain or swelling. The most significant difference between Dermatomyositis and Polymyositis in terms of symptoms is that a rash also occurs with Dermatomyositis that does not occur with Polymyositis .

When dermatomyositis and polymyositis are severe, they can cause problems with things like swallowing. This is serious because it can cause a person to choke or breathe things into their lungs. In the rarest and worst of cases, it can even impact the muscle of the heart and the muscles used for breathing.

Dermatomyositis and Polymyositis are types of inflammatory myopathies, which refer to diseases that cause inflammation of the muscles.

While anyone can get Dermatomyositis or Polymyositis, they most often affect two age groups: children aged 10 to 15 and adults aged 45 to 60. Myositis is very rare: it affects only about 10 people in every million. Women are about 2 times more likely to get myositis than men.

Autoimmune Disease

Dermatomyositis and Polymyositis are autoimmune diseases, meaning that they occur because the body’s immune system is attacking its own healthy cells and tissues. The reason why it does this in some people is not well understood. When the body’s immune system is “activated” in this way, it can make a person feel very tired, similar to when they have the flu.

Types of Myositis

This article will refer to dermatomyositis and polymyositis as myositis. Note that there are other types of myositis that are not related to the autoimmune disorders dermatomyositis and polymyositis discussed in this article.

Myositis can exist on its own, or it can sometimes be seen along with other rheumatic diseases. Muscle inflammation can be seen with Sjogren’s syndrome, lupus, and systemic sclerosis (scleroderma).

In a small number of people, myositis can be accompanied by a cancer that somehow triggers the immune system and causes the condition. Everyone who gets myositis should be screened for cancer.

Understanding Myositis


Myositis Patient Guide