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Dermatomyositis and Polymyositis are two forms of inflammatory myopathies - diseases of muscle caused by an immune response. They cause muscle weakness as their major symptom, and dermatomyositis also causes a skin rash. Both are thought to be autoimmune diseases, in which the body's immune system attacks the muscles.
Because the causes, symptoms and treatments are similar, polymyositis and dermatomyositis are often discussed as a pair.
Incidence
It is estimated that polymyositis and dermatomyositis combined affect some 20,000 people in the United States, with approximately 1,400 new adult cases per year. These conditions are two to three times as common among blacks as whites, and twice as common among women as men. They may appear at any age, but begin most commonly between the ages of 40 and 60. A juvenile form of dermatomyositis also occurs, with approximately 2,000 new cases per year in the United States. It appears most commonly in middle childhood to early adolescence (ages 5-15).
Signs & Symptoms
Symptoms of dermatomyositis usually begin gradually, with muscle weakness, joint pain, fever, weight loss, and fatigue. Children may experience a more rapid onset. Muscle weakness usually affects the upper arms, neck, and legs, on both sides of the body. Some people experience joint and muscle pain, and some have difficulty swallowing.
As the disease progresses, the muscles begin to waste away (atrophy) and permanently shorten (contracture). A grayish-red/violet rash appears at the same time as the muscle weakness. The rash commonly appears on the face and includes a purplish swelling, called a heliotrope, around the eyes/eyelids. There may be a shawl-like rash over the neck, shoulders, and upper chest and back. Another rash often appears around the joints, especially around the fingers but also on the knees and elbows. This rash may be smooth or have hard/scaly patches, and is called Gottron's sign. When the rash fades, it leaves behind pigmented patches of skin.
Exposure to sun can worsen existing areas or lead to the development of new ones. Hard nodules of calcium deposits under the skin (calcinosis) are common in juvenile dermatomyositis, but not in the adult form.
Some people with dermatomyositis develop a rash without muscle weakness. This is called dermatomyositis sine myositis. Others may also have Raynaud's phenomenon, in which the small arteries in the fingers and toes constrict, causing the skin to look pale or bluish, usually after exposure to cold.
The muscle weakness may appear suddenly and progress over weeks to months. Patients may have difficulty raising the arms above the shoulders, climbing steps, or arising from a sitting position, and be unable to raise the head from the pillow. Patients may become wheelchair bound or bedridden because of weakness of pelvic and shoulder girdle muscle groups. The flexors of the neck may be severely affected. Weakness of the laryngeal musculature is responsible for dysphonia. Involvement of the striated muscle of the pharynx and upper portion of the esophagus leads to dysphagia and regurgitation. A diminution in peristaltic activity and dilation of the lower esophagus and small intestine may be present. The muscles of the hands, feet and face escape involvement. Contractures of limbs may develop late in the chronic stage.
Diagnosis & Tests
Dermatomyositis is diagnosed through a thorough physical exam and the characteristic symptoms. A doctor will order diagnostic tests to check levels of certain enzymes in the bloodstream. He or she will also take a small sample of tissue from the affected muscle (a muscle biopsy), to check for abnormalities. A test called electromyography will reveal any abnormal electrical activity in the muscles. Magnetic resonance imaging (MRI) is also helpful in revealing muscle inflammation. The doctor should order blood tests and other cancer-screening tests to check for malignancies because people with dermatomyositis are more likely to develop malignant cancers.
Treatment & Prevention
The first line of treatment for dermatomyositis is restricted activity and a daily injection of a corticosteroid, such as prednisone, to reduce inflammation and relieve pain. This dose is gradually decreased as the condition improves. Adults usually need to stay on a maintenance dose for life. However, children may be able to stop steroid treatment after approximately one year. Some patients cannot tolerate or do not respond to corticosteroids - they may instead be treated with immunosuppressive drugs, such as azathioprine or methotrexate. Other patients may respond well to intravenous immune globulin. Dermatomyositis often improves with treatment of malignant tumors.
While there is no known way to prevent dermatomyositis, you can find relief from symptoms and possible remission by following your doctor's treatment recommendations. It is very important to reduce your physical activity until your muscles have had an opportunity to recover.
Complications
People with polymyositis or dermatomyositis are more likely to have other autoimmune diseases. Arthritis is common, as is Raynaud's phenomenon; others include systemic lupus erythematosus and Sjögren's syndrome.
Interstitial lung disease occurs in 10-30% of all people with polymyositis or dermatomyositis. This condition causes fibrous scarring of lung tissue, leading to a dry, unproductive cough and shortness of breath with exertion.
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Signs, symptoms & indicators of Dermatomyositis:
Conditions that suggest Dermatomyositis:
Recommendations and treatments for Dermatomyositis:
KEY | | Weak or unproven link |  | | Strong or generally accepted link |  | | Likely to help |
GLOSSARY
Arterial (Arteries, Artery)
Blood that leaves the heart. When it leaves the right ventricle, it is venous blood; and when it leaves the left ventricle, through the aorta, it is fresh and oxygenated. After it has passed out to the capillaries and started to return, it is venous blood.
Arthritis (Arthritic)
Inflammation of a joint, usually accompanied by pain, swelling, and stiffness, and resulting from infection, trauma, degenerative changes, metabolic disturbances, or other causes. It occurs in various forms, such as bacterial arthritis, osteoarthritis, or rheumatoid arthritis. Osteoarthritis, the most common form, is characterized by a gradual loss of cartilage and often an overgrowth of bone at the joints.
Autoimmune Disease (Autoimmune, Autoimmunity)
One of a large group of diseases in which the immune system turns against the body's own cells, tissues and organs, leading to chronic and often deadly conditions. Examples include multiple sclerosis, rheumatoid arthritis, systemic lupus, Bright's disease and diabetes.
Biopsy
Removal of a sample of tissue from a living being for diagnosis. A pathologist later uses a microscope to look for certain features, such as cancer cells, in the sample. A fine-needle aspiration biopsy involves inserting a thin needle to remove a small amount of tissue, sometimes using CT or ultrasound to guide the needle. A core biopsy involves obtaining a sample of tissue with a thick needle or by inserting a thin, lighted tube (laparoscope) into a small incision in the abdomen. Another biopsy method is to remove tissue during an operation.
Calcium
The body's most abundant mineral. Its primary function is to help build and maintain bones and teeth. The body also needs calcium to carry nerve signals, keep the heart functioning, contract muscles, clot blood and maintain healthy skin. Calcium helps control blood acid-alkaline balance, plays a role in cell division, muscle growth and iron utilization, activates certain enzymes, and helps transport nutrients through cell membranes. Calcium also forms a cellular cement called ground substance that helps hold cells and tissues together.
Chronic (Chronicity)
Usually referring to chronic illness: Illness extending over a long period of time.
Contracture (Contractures)
An abnormal, often permanent shortening, as of muscle or scar tissue, that results in distortion or deformity, especially of a joint of the body.
Corticosteroid (Corticosteroids)
Steroid hormone produced by the adrenal cortex.
Dermatomyositis
A diffuse connective tissue disease.
Dysphagia
Difficulty in swallowing.
Dysphonia
Difficulty in speaking, usually evidenced by hoarseness.
Enzymes (Enzyme)
Specific protein catalysts produced by the cells that are crucial in chemical reactions and in building up or synthesizing most compounds in the body. Each enzyme performs a specific function without itself being consumed. For example, the digestive enzyme amylase acts on carbohydrates in foods to break them down.
Esophagus (Esophageal)
Commonly called the "food pipe", it is a narrow muscular tube, about nine and a half inches long, that begins below the tongue and ends at the stomach. It consists of an outer layer of fibrous tissue, a middle layer containing smoother muscle, and an inner membrane, which contains numerous tiny glands. It has muscular sphincters at both its upper and lower ends. The upper sphincter relaxes to allow passage of swallowed food that is then propelled down the esophagus into the stomach by the wave-like peristaltic contractions of the esophageal muscles. There is no protective mucosal layer, so problems can arise when digestive acids reflux into the esophagus from the stomach.
Flexor (Flexors)
A muscle that closes a joint.
Immune System (Immune Response, Immunity)
A complex that protects the body from disease organisms and other foreign bodies. The system includes the humoral immune response and the cell-mediated response. The immune system also protects the body from invasion by making local barriers and inflammation. The process may involve acquired immunity (the ability to learn and remember a specific infectious agent), or innate immunity (the genetically programmed system of responses that attack, digest, remove, and initiate inflammation and tissue healing).
Larynx (Laryngeal, Voice Box)
The short passageway shaped like a triangle that is just below the pharyx in the neck.
Lung (Lungs, Pulmonary)
Organ of the body, located in the chest cavity which is designed to bring oxygen from the air into the blood stream, while also expelling carbon dioxide and other waste gases out of the body. Pulmonary: Related to the lungs.
Magnetic Resonance Imaging (MRI)
A technique used in diagnosis that combines radio waves and magnetic forces to produce detailed images of the internal structures of the body.
Malignant (Cancerous)
Dangerous. Mainly used to describe a cancerous growth -- when used this way, it means the growth is cancerous and predisposed to spreading.
Pharynx (Pharyngeal)
A hollow tube about five inches long that starts behind the nose and goes down to the neck to become part of the esophagus (the tube that goes to the stomach).
Raynaud's Phenomenon (Raynaud's, Raynauds Disease, Raynaud's Disease, Raynauds Phenomenon, Raynauds Syndrome, Raynaud's Syndrome)
Raynaud's disease or syndrome is a disorder of blood circulation, mainly in the fingers and toes. It is of unknown cause and characterized by changes of the skin that are aggravated by exposure to cold: first, becoming white with numbness and pain as a result of inadequate oxygenation of the blood, then red/purple with a burning sensation. The sudden constriction of blood vessels causes decreased blood flow to the extremities and can, in extreme cases, lead to gangrene. Also called "white finger", "wax finger" or "dead finger".
Small Intestine (Small Bowel)
The small intestine lies between the stomach and the large intestine. It is about 6 meters (20 feet) long and its primary function is to digest (break down) food and absorb nutrients (vitamins, minerals, proteins, carbohydrates, and fats). The small intestine makes up more than 70% of the length and 90% of the surface area of the gastrointestinal (GI) tract.
Steroid (Steroids)
Any of a large number of hormonal substances with a similar basic chemical structure containing a 17-carbon 14-ring system and including the sterols and various hormones and glycosides.
Striated Muscle (Skeletal Muscle, Voluntary Muscle)
The human body contains 2 types of muscle - smooth muscle and striated (skeletal) muscle. Striated muscle (striped when seen under the microscope) is the muscle that allows us to move our arms and legs and other body parts on purpose - that is, voluntary movement.
Syndrome
A medical condition characterized by a collection of related symptoms (what the patient feels) and signs (what a doctor can observe or measure).
Last updated: Oct 18, 2009
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