What are Inflammatory Myopathies?

The inflammatory myopathies are a group of muscle diseases that cause chronic inflammation of the muscles and are accompanied by muscle weakness. These conditions are thought to be autoimmune in nature, and may be triggered by environmental factors in genetically susceptible people. There are four main types of inflammatory myopathies, including juvenile myositis, polymyositis, dermatomyositis, and inclusion body myositis (IBM). They are treated with steroid hormones, such as prednisone, and immune system suppressant medications. Inflammatory myopathies caused by a virus or exposure to a harmful substance may subside when the acute illness phase passes.

Diagnosis of the inflammatory myopathies can be made after a muscle biopsy test, which shows damaged muscle fibers and inflammation in the muscles. Blood tests will show inappropriate levels of muscle enzymes and antibodies. An electromyography may be ordered to demonstrate the electrical activity of the muscles when they are at rest and during muscle contractions.

Treatment of inflammatory myopathies focuses on relieving the symptoms associated with the condition. Steroid drugs can alleviate the inflammation in polymyositis and dermatomyositis, but it is not effective for IBM. Some patients are treated with immunosuppressant drugs. Physical therapy and heat therapy can help relieve pain and maintain range of motion for some people.

Juvenile myositis usually begins between the ages of two and 15. It is characterized by muscle pain and inflammation of the proximal muscles. The muscle pain may be caused by a shortening of the tendons and muscles near the joints, which inhibits free muscle movement. Many children with juvenile myositis have skin rashes, abdominal pain, and frequent fevers. The muscle fatigue may cause a condition called dysphagia, which means difficulty swallowing, and nutritional deficits may result in weight loss.

Adult polymyositis is very similar to the juvenile version. It affects the muscles on both sides of the body at the same time. People with inflammatory myopathies generally have trouble with many simple daily activities. The muscle pain and weakness can cause difficulty standing, walking, and swallowing food.

IBM is a systemic muscle wasting disease. The muscles affected may be only on one side of the body. Small holes called vacuoles develop in the muscle fibers leading to muscle atrophy. The condition usually begins with an inability to pick up small objects, and progresses to widespread muscle weakness. IBM does not respond well to any medications.

Both children and adults can develop dermatomyositis. It is characterized by the eruption of a purplish or red rash that develops on the hands, feet, knees, and elbows. The rash occurs before signs of muscle weakness and pain, and may form on areas of the body such as the head, chest, and back. In some cases, dermatomyositis accompanies cancer or scleroderma, a hardening of the connective tissue.