Helping raise awareness of Myositis

Myositis is defined as inflammation of the muscles. The inflammatory myopathies are a group of disorders characterized by inflammation and weakness mainly of the muscles closest to the trunk of the body. These groups of disorders include Polymyositis (PM), Dermatomyositis (DM), and Inclusion Body Myositis (IBM).

Dermatomyositis and Polymyositis cause inflammation of the muscles. These are rare disorders, together affecting only about one in 100,000 people per year. More women than men are affected. 


  • Dermatomyositis (DM) is the easiest type of myositis to diagnose because of the skin rash which is often seen before any muscle weakness is felt. The DM rash looks patchy, dusky, and reddish or purple. It is found on the eyelids, cheeks, nose, back, upper chest, elbows, knees and knuckles. Some people also have hardened bumps under the skin, called calcinosis. The skin rash and weak muscles are caused by inflammation, or swelling, in the blood vessels under the skin and in the muscles, also called vasculitis. Patients who have the skin rash but feel no muscle weakness have amyopathic DM, or DM sine myositis.
  • Polymyositis (PM) is found mostly in people over the age of 20 and affects more women than men. Muscle weakness usually happens over days, weeks or months. The weakness begins with muscles closest to and within the trunk of the body. Neck, hip, back and shoulder muscles are examples. Some patients also have weakness in muscles farther from the trunk, like hands and fingers. Some PM patients experience muscle pain, breathing problems, and trouble swallowing.
  • Inclusion Body Myositis (IBM) The onset of muscle weakness in IBM is generally gradual (over months or years) and affects both proximal (close to the trunk of the body) and distal (further away from the trunk) muscles. Muscle weakness may affect only one side of the body. Inclusion body myositis primarily affects men after the age of 50 but can also affect women. The disease generally progresses slowly and does not affect life expectancy of those affected. The disease is generally unresponsive to corticosteroids and immunosuppressive drugs. Some evidence suggests that intravenous immunoglobulin may have a slight, but short-lasting, beneficial effect in a small number of cases. Prednisone is also used for treatment, although its benefit has not been proven.
  • These rare diseases are Autoimmune (AI) disorders. A normal immune system defends the body from infections and diseases. It is designed to attack and destroy foreign invaders like viruses, bacteria, and parasites. A misdirected immune response is referred to autoimmunity where your immune system attacks the healthy cells in your body by mistake causing muscle inflammation, weakness, and damage.