Patient education: Polymyositis, dermatomyositis, and other forms of idiopathic inflammatory myopathy (Beyond the Basics)
- Marc L Miller, MD
Marc L Miller, MD
- Clinical Assistant Professor of Medicine
- Tufts University School of Medicine
IDIOPATHIC INFLAMMATORY MYOPATHIES
The idiopathic inflammatory myopathies are a group of diseases in which inflammation occurs in muscles and often in organs and tissues other than muscle. Included in this group are various conditions whose names contain the term “myositis,” which simply means muscle inflammation:
●Myositis that occurs with other systemic (body-wide) rheumatic diseases, such as mixed connective tissue disease, lupus, and scleroderma
●Autoimmune necrotizing myopathy
The cause of the idiopathic inflammatory myopathies remains undetermined. All are thought to be due to immune system abnormalities leading to the development of inflammation in muscle and other tissues.
These are rare disorders, together affecting only about 1 in 100,000 people per year. More women than men are affected. Although the peak age of onset is in the 50s, the disorders can occur at any age. The word “juvenile” is used in the name when a child is affected by myositis.
Clinical manifestations — The main symptom that is common to the inflammatory myopathies is muscle weakness. Other symptoms that indicate involvement of body systems other than muscle can occur.
Muscle weakness — Typically patients develop painless weakness of the proximal muscles—the large muscle groups of the upper arms, thighs, neck, and trunk—in a symmetric pattern affecting both sides of the body. The smaller distal muscles of the hands, wrists, feet, and ankles are usually not affected. Patients may notice difficulty rising from a chair, climbing stairs, or performing tasks overhead such as reaching up to a high shelf, while grip strength remains normal. At times there may be mild muscle soreness. The weakness usually develops over several weeks to months.
The throat and upper esophagus consist of muscle identical to the muscles that control voluntary movement. As a result of weakness in these muscles, some patients will develop difficulty swallowing or may aspirate food into the lungs, which can lead to pneumonia.
Skin changes — People with dermatomyositis often develop a rash or other changes in the skin. Sometimes the rash develops before muscle problems occur. In some cases, the rash of dermatomyositis appears, but muscle weakness never develops. Several types of rash may occur:
●Gottron’s sign or Gottron’s papules – Gottron’s sign is a flat red rash over the back of the fingers, elbows or knees. Gottron’s papules are red, often scaly, bumps overlying the knuckles of the fingers (picture 1).
●Shawl sign – The shawl sign is a widespread, flat, reddened area that appears on the upper back, shoulders, and back of the neck. It can worsen with exposure to ultraviolet light.
●V sign – The V sign has an appearance similar to that of the shawl sign, but appears on the front of the chest in the area of skin exposed by a V-necked sweater.
●Heliotrope rash – The heliotrope rash is located on the upper eyelids and is often accompanied by eyelid swelling (picture 2). The heliotrope sign is named for the heliotrope flower, which is violet-colored.
●Mechanic's hands – People with dermatomyositis or polymyositis may develop “mechanic's hands,” a roughening and cracking of the skin of the tips and sides of the fingers, resulting in irregular, dirty-appearing lines that resemble those of a manual laborer (picture 5).
●Scalp – Changes in the scalp resembling psoriasis may occur in people with dermatomyositis.
Lung disease — Interstitial lung disease (inflammation of lung tissue) occurs most commonly in patients with anti-synthetase antibodies in their blood. These patients may develop a cough and shortness of breath with exertion that ranges from mild symptoms to severe, progressive respiratory distress.
Antisynthetase syndrome — This subgroup of patients all have one of a family of antibodies in their blood termed the anti-synthetase antibodies. Anti-Jo-1 antibody is the most common and is found in about 20 percent of dermatomyositis patients. This subgroup is characterized by rashes (particularly mechanic’s hands), interstitial lung disease, fever, arthritis, and Raynaud’s phenomenon (in which the fingers turn white on cold exposure) in addition to muscle disease.
Juvenile dermatomyositis — Children with inflammatory myopathy usually but not always have a dermatomyositis rash. They differ from adults most importantly in that painful calcium deposits can form on the skin and on the fibrous tissue that wraps around muscles, called fascia.
Other systemic rheumatic diseases — When myositis accompanies scleroderma or systemic lupus, the myositis does not always cause symptoms. Some people have mild muscle weakness, while others have only abnormal blood muscle enzymes to indicate the presence of the disease.
Cancer — People with inflammatory myopathies, especially adults with dermatomyositis who do not have anti-synthetase antibodies (see 'Antisynthetase syndrome' above), have an increased risk of cancer. This risk increases with age and involves the same common cancers that affect the general population, including cancer of the lung, breast, prostate, and ovaries. In many cases, people newly diagnosed with polymyositis or dermatomyositis should also be screened for cancer. This may include blood tests, chest X-ray, colonoscopy, Pap test, and/or mammogram (depending on the person's age and sex).
Diagnosis — The diagnosis of the inflammatory myopathies involves a careful history, a thorough physical exam, and some blood tests. People who have these conditions often have muscle weakness and/or typical skin changes, and blood tests showing evidence of muscle damage or the presence of antibody markers that signal these diseases. Nearly all patients with myositis will have elevation of creatine kinase (CK) levels. Many will have antinuclear antibodies (ANA) or one of the anti-synthetase antibodies in their blood. Some myositis patients however will be “serologically silent,” meaning they have no antibody markers.
In patients in whom it is difficult to determine the cause of muscle weakness, other tests may be useful. A magnetic resonance imaging (MRI) scan of the muscles, for example, can demonstrate changes suggesting muscle inflammation, while an electromyogram (EMG) can demonstrate abnormal electrical activity in muscles, also indicating muscle injury. An EMG is usually performed by a neurologist and involves inserting small needles into muscles, usually of the arms or legs, and recording the electrical potentials generated by the muscle. EMG testing can help distinguish weakness due to muscle disease from weakness due to nerve problems.
A muscle biopsy is a procedure that removes a small piece of muscle through an incision in the skin. The specimen is prepared with special stains and a pathologist then examines it for evidence of muscle inflammation and for specific characteristics of polymyositis or dermatomyositis. Muscle biopsy is the most accurate test to definitively diagnose dermatomyositis or polymyositis but may not be necessary to establish the diagnosis in cases with typical presentations and characteristic rash.
Other conditions that can cause muscle weakness and need to be distinguished from the inflammatory myopathies include:
●Hypothyroidism (usually severe cases).
●Drug-induced myopathies – Drugs that can cause myopathy include statin drugs, used to treat elevated cholesterol; prednisone, in high and prolonged doses; and colchicine, used on a daily basis in patients with kidney disease.
●Muscular dystrophies, which have specific patterns of weakness and may be familial.
●Metabolic myopathies – These are rare conditions that are due to abnormalities in enzymes involved in the metabolism of carbohydrates or fats.
●Electrolyte abnormalities, such as severe potassium depletion.
●Infections (most commonly viral).
●Inclusion body myositis – This is a rare disease that most often affects older men and causes slowly progressive weakness that tends to involve distal muscles, such as those in the hands, as well as proximal muscles. The diagnosis for this condition is established by characteristic changes on muscle biopsy.
Treatment — Treatment of the inflammatory myopathies is usually initiated with prednisone. Prednisone is a form of cortisone that in high doses is a very effective antiinflammatory agent.
In patients treated with prednisone, muscle enzyme levels will begin to fall in a few weeks and muscle strength usually recovers within a few months. Unfortunately, high-dose prednisone can also cause numerous side effects, including weight gain and redistribution of body fat to the face, neck, and abdomen; elevated blood sugar; mood swings; thinning of the skin; and osteoporosis. For this reason, it is important to use the lowest dose for the shortest time that controls the disease.
Methotrexate or azathioprine is usually added early in the treatment course in order to minimize the use of prednisone. While these medications do have some side effects, they are often effective in controlling the disease long-term and they can be used safely in the vast majority of patients. Methotrexate is taken orally or by injection on a weekly basis. Blood counts and liver tests are monitored periodically. Azathioprine is an oral daily medication and can sometimes cause anemia.
For those patients who are resistant to treatment with either methotrexate or azathioprine, other treatment options include a combination of both methotrexate and azathioprine, intravenous immune globulin, mycophenolate, or rituximab.
Hydroxychloroquine (an antimalarial drug related to quinine and chloroquine) is often effective in the treatment of dermatomyositis rashes.
Since polymyositis and dermatomyositis cannot be cured but can be controlled by medications, it is important for patients with these diseases to be monitored long-term for signs of disease reactivation. That way, appropriate adjustments in treatment can be made. Patients need to have their CK level and muscle strength tested on a regular basis.
General measures — In addition to medications, people with dermatomyositis or polymyositis should take precautions to prevent complications related to the disease and its treatments. These precautions include:
●Osteoporosis prevention – A calcium supplement with vitamin D and a prescription medication to prevent osteoporosis, such as one of the bisphosphonates, are often recommended in patients treated with prednisone. The potential benefits and possible side effects of such medications should be discussed with a healthcare provider. (See "Patient education: Calcium and vitamin D for bone health (Beyond the Basics)" and "Patient education: Osteoporosis prevention and treatment (Beyond the Basics)".)
●Exercise – Physical therapy and rehabilitation should begin soon after the diagnosis of dermatomyositis or polymyositis to prevent contractures (shortening of the muscle that can limit joint movement).
●Avoidance of sunlight – Since the rash of dermatomyositis is often worsened by sun exposure, people with dermatomyositis should protect themselves from the sun by using sunscreen or seeking shade. (See "Patient education: Sunburn prevention (Beyond the Basics)".)
●Aspiration prevention – Patients who have trouble swallowing must take care to avoid inhaling (aspirating) foods and drinks. This may be done by elevating the head of the bed, by adding thickening agents to drinks, or, in severe cases, by having a feeding tube placed in the stomach.
●Pneumonia prevention – The medications used to treat dermatomyositis and polymyositis (glucocorticoids, azathioprine, and methotrexate) weaken the immune system. This can increase the risk of certain infections, including a type of pneumonia called Pneumocystis. To decrease this risk, an antibiotic may be recommended.
Pregnancy and inflammatory myopathy — Little information is available regarding the impact of pregnancy on inflammatory myopathies or the impact of inflammatory myopathies on pregnancy. The data that are available indicate that complications of pregnancy are less likely in women who have inactive disease. Complications may include a smaller than normal infant, stillbirth, or premature birth.
Women with polymyositis or dermatomyositis who want to become pregnant should discuss their condition and current medications with a rheumatologist or maternal fetal medicine specialist before trying to conceive. Some medications, particularly methotrexate, are not safe for use during pregnancy due to a seriously increased risk of miscarriage and birth defects.
Dermatomyositis and polymyositis prognosis — The severity of disease in a person with dermatomyositis or polymyositis is highly variable, ranging from mild weakness that responds well to treatment to a rapid progression of symptoms that are unresponsive to all treatments. Less commonly, people with these conditions improve spontaneously without any treatment.
People with dermatomyositis or polymyositis tend to have a better outcome if they are treated promptly, have mild muscle weakness, have no difficulty swallowing, and have no signs of disease in other organ systems such as the heart and lungs.
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Clinical manifestations of dermatomyositis and polymyositis in adults
Clinical manifestations and diagnosis of inclusion body myositis
Clinical manifestations of mixed connective tissue disease
Management of inclusion body myositis
Juvenile dermatomyositis and polymyositis: Diagnosis
Initial treatment of dermatomyositis and polymyositis in adults
Interstitial lung disease in dermatomyositis and polymyositis: Clinical manifestations and diagnosis
Interstitial lung disease in dermatomyositis and polymyositis: Treatment
Malignancy in dermatomyositis and polymyositis
Juvenile dermatomyositis and polymyositis: Epidemiology, pathogenesis, and clinical manifestations
Juvenile dermatomyositis and polymyositis: Treatment, complications, and prognosis
Treatment of recurrent and resistant dermatomyositis and polymyositis in adults
Overview of viral myositis
The following organizations also provide reliable health information.
●National Library of Medicine
●American Academy of Family Physicians
●National Institute of Arthritis and Musculoskeletal and Skin Diseases
●American College of Rheumatology
- Dalakas MC. Inflammatory muscle diseases. N Engl J Med 2015; 372:1734.
- O'Connell MJ, Powell T, Brennan D, et al. Whole-body MR imaging in the diagnosis of polymyositis. AJR Am J Roentgenol 2002; 179:967.
- Lundberg IE. Idiopathic inflammatory myopathies: why do the muscles become weak? Curr Opin Rheumatol 2001; 13:457.
- Amato AA, Barohn RJ. Evaluation and treatment of inflammatory myopathies. J Neurol Neurosurg Psychiatry 2009; 80:1060.
- Distad BJ, Amato AA, Weiss MD. Inflammatory myopathies. Curr Treat Options Neurol 2011; 13:119.
All topics are updated as new information becomes available. Our peer review process typically takes one to six weeks depending on the issue.