Myositis is a rare disease in which the immune system chronically inflames the body's own healthy muscle tissue. The muscles are progressively weakened by persistent inflammation.
Specific forms of myositis include:
• Polymyositis (PM), which inflames muscles in the trunk
• Inclusion body myositis (IBM), which effects mostly men in their 50s
• Dermatomyositis (DM), which effects muscle fibers and skin and causes a rash
• Juvenile myositis (JM), which mostly effects children and causes muscle weakness, skin rash and swallowing trouble
The causes of myositis are currently unknown.
The initial symptoms of myositis are weakness and pain in the muscles of the hips and shoulders, making it difficult to rise from a chair. Myositis can also affect the muscles in the front of the neck and throat, making it hard to speak or swallow, a condition known as dysphagia.
Other symptoms include:
• Breathing trouble
• A rash on the face or knuckles
• Joint pain and swelling