Polymyositis (PM) is an inflammatory muscle disease with an unknown cause. The disease has a gradual onset and generally begins in the second decade of life and, thus, it rarely affects persons under the age of 18. It causes muscles to exhibit varying degrees of decreased strength, usually affecting those muscles that are closest to the trunk of the body. Trouble with swallowing (dysphagia) may occur with polymyositis.
In polymyositis, muscles exhibit varying degrees of weakness, evolving gradually over weeks to months. It is known that PM begins when white blood cells, the immune cells of inflammation, spontaneously invade muscles, and is thus termed an autoimmune disease. In PM, muscle fibers are found to be in varying stages of necrosis (tissue death) and regeneration. The muscles affected are typically those closest to the trunk or torso, resulting in weakness that can be severe. Eventually, patients have difficulty rising from a sitting position, climbing stairs, lifting objects, or reaching overhead. In some cases, distal muscles (those not close to the trunk of the body) may also be affected later in the course of the disease. Polymyositis is a chronic illness with periods of increased symptoms, called flares or relapses, and decreased symptoms, known as remissions.
Polymyositis mimics many other muscle disorders and remains a diagnosis of exclusion. It should be viewed as a syndrome of diverse causes that occurs separately or in association with other autoimmune disorders or viral infections. A similar inflammatory myopathy is often associated with skin rash and is referred to as dermatomyositis .
Polymyositis in the United States is most common among African Americans. The disorder is most prevalent in women in a male/female ratio of 1:2. In the United States, its incidence is one per 100,000 persons per year; internationally, a lower incidence among the Japanese has been observed. The age of onset is normally above the second decade of life and it is rare or nonexistent for persons under the age of 20.
Causes and symptoms
To date, no cause of polymyositis has been isolated by scientific researchers. While the initial inciting agent remains unknown, possibilities include infection with certain viruses or muscle trauma. There are many infectious agents that are thought to trigger the disease, mainly Coxsackie virus B1, HIV, human T-lymphotropic virus 1 (HTLV-1), hepatitis B and C, influenza, echovirus, and adenovirus. Certain drugs are also thought to be potential triggers, including D-penicillamine, hydralazine, procainamide, and phenytoin.
There are indicators of heredity (genetic) susceptibility that can be found in some patients, mainly the HLA (human leukocyte antigen) genes, which are responsible for encoding some proteins that can activate the immune system.
The muscle weakness affecting mainly the proximal (closest to the trunk of the body) muscles is the first sign of PM. The onset can be gradual or rapid, but normally progresses over weeks or months. This results in varying degrees of loss of muscle strength and atrophy (tissue degeneration). The loss of strength can be noticed as difficulty getting up from chairs, climbing stairs, or lifting above the shoulders. Trouble with swallowing (dysphagia) and weakness lifting the head from the pillow may occur. Occasionally, the muscles ache at rest or with use, and are tender to the touch (occurs in about 25% patients). Persons with polymyositis can also feel fatigue , a general feeling of discomfort, and have weight loss, and/or low-grade fever. Heart and lung involvement can lead to irregular heart rhythm and shortness of breath.
Persons with polymyositis generally seek initial medical help due to weakness. A physician typically reviews the condition of other body systems, including the skin, heart, lungs, and joints. Blood tests are helpful to reveal abnormal high levels of muscle enzymes in the serum of PM patients, mainly creatinine phosphokinase (CPK) and aldolase. In PM, muscle damage causes the muscular cells to break open and spill their content into the bloodstream. Since most of CPK and aldolase exist in muscles, an increase in the amount of these enzymes in the blood indicates that muscle damage has occurred, or is occurring. Blood tests can also point to active inflammation.
The muscle biopsy is one of the best ways to diagnose myositis and other muscle disorders. A muscle biopsy is used to confirm the presence of muscle inflammation typical only of polymyositis. This is a surgical procedure whereby muscle tissue is removed for analysis by a pathologist, a specialist in examining tissue under a microscope. Muscles often used for biopsy include the quadriceps muscle of the front of the thigh, the biceps muscle of the arm, and the deltoid muscle of the shoulder. The results can show conditions such as inflammation, or swelling, of the muscle, damage to the muscle, and loss of muscle mass, or atrophy.
Imaging of the muscles using radiology tests such as magnetic resonance imaging (MRI ) can show areas of inflammation of muscle, swelling, or scarring. This sometimes can be used to determine muscle biopsy sites. MRIs show signal intensity abnormalities of muscle due to inflammation.
Another test, an electromyogram (EMG), is used to measure the activity of muscles and to provide clues to the cause of muscle weakness or paralysis, muscle problems such as muscle twitching, numbness, tingling, or pain , and nerve damage or injury. EMG is useful in the diagnosis of PM and to exclude other nerve-muscle diseases. Although EMG and MRI imaging are helpful in many cases, the diagnosis of PM is definite when a patient has subacute elevated levels of serum creatine kinase and characteristic findings on muscle biopsy.
A neurologist or rheumatologist is the primary consultant for PM, with allied health care areas that include, but are not limited to, physical therapy.
In PM, high-dose corticosteroids constitute the first line of treatment, and are effective in more than 70% of patients. Alternatives include immunosuppressant medications, notably azathioprine, methotrexate, and intravenous immunoglobulins (IVIg).
Recovery and rehabilitation
Before the era of corticosteroids, PM was a particularly severe disease with a spontaneous survival rate of less than 40%. Polymyositis in adults now has a relatively favorable prognosis, with a five-year survival rate of around 90%. Only 30–50% of persons with polymyositis achieve complete recovery; the majority of patients have persistent functional problems. However, patients can ultimately do well, especially with early medical treatment of disease and early recognition of disease flares. The disease frequently becomes inactive, and rehabilitation of atrophied (withered) muscles becomes a long-term project.
The National Institute of Environmental Health Sciences (NIEHS) is recruiting patients for a study entitled "Myositis in Children." The aim of the study is to learn more about the immune system changes and medical problems associated with myositis. The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) is examining whether infliximab (Remicade[r]) is safe for treatment of PM. Updated information is available at The National Institutes of Health website for clinical trials at <http://www.clinicaltrials.gov>.
The prognosis for PM and the response to therapy vary from very good to satisfactory. Most patients respond well to treatment, although residual weakness is common. Osteoporosis, a common complication of chronic corticosteroid therapy, may be significant. For African Americans, older people, females, people with interstitial lung disease and associated malignancies, those who delay treatment, and those with trouble swallowing or heart involvement, the prognosis is much less favorable.
Exercise is generally beneficial, and helps to get the most out of diseased muscles. Falls and injuries, however, can cause substantial disability. People with PM, therefore, have the difficult task of undertaking regular exercise within their capability, but avoiding injury through accident. Because weakened muscles cannot carry an excess load, keeping to an ideal weight is critical. Although this may seem obvious, weight control is more difficult when exercise is limited.
A well-balanced diet is helpful. Patients with severe inflammation of the muscles may need extra protein. Feeding should be avoided prior to bedtime in patients with trouble swallowing.
Staff. The Official Patient's Sourcebook on Polymyositis: A Revised and Updated Directory for the Internet Age. San Diego: Icon Health International, 2004.
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Myositis Association of America. 755 Cantrell Ave., Suite C, Harrisonburg, VA 22801. (540) 433-7686; Fax: (540) 432-0206. firstname.lastname@example.org. <http://www.myositis.org>.
Marcos do Carmo Oyama
Iuri Drumond Louro, MD, PhD
do Carmo Oyama, Marcos; Louro, Iuri. "Polymyositis." Gale Encyclopedia of Neurological Disorders. 2005. Encyclopedia.com. (May 27, 2016). http://www.encyclopedia.com/doc/1G2-3435200284.html
do Carmo Oyama, Marcos; Louro, Iuri. "Polymyositis." Gale Encyclopedia of Neurological Disorders. 2005. Retrieved May 27, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3435200284.html
Polymyositis is an inflammatory muscle disease causing weakness and pain. Dermatomyositis is identical to polymyositis with the addition of a characteristic skin rash.
Polymyositis (PM) is an inflammatory disorder in which muscle tissue becomes inflamed and deteriorates, causing weakness and pain. It is one of several types of inflammatory muscle disease, or myopathy. Others include dermatomyositis (DM) and inclusion body myositis. All three types are progressive conditions, usually beginning in adulthood. A fourth type, juvenile dermatomyositis, occurs in children. Although PM and DM can occur at any age, 60% of cases appear between the ages of 30 and 60. Females are affected twice as often as males.
Causes and symptoms
The cause of PM and DM is not known, but it is suspected that a variety of factors may play a role in the development of these diseases. PM and DM may be autoimmune diseases, caused by the immune system's attack on the body's own tissue. The reason for this attack is unknown, although some researchers believe that a combination of immune system susceptibility and an environmental trigger may explain at least some cases. Known environmental agents associated with PM and DM include infectious agents such as Toxoplasma, Borrella (Lyme disease bacterium), and coxsackievirus. Most cases, however, have no obvious triggers (direct causative agents). There may also be a genetic component in the development of PM and DM.
The early symptoms of PM and DM are slowly progressing muscle weakness, usually symmetrical between the two sides of the body. PM and DM affect primarily the muscles of the trunk and those closest to the trunk, while the hands, feet, and face usually are not involved. Weakness may cause difficulty walking, standing, and lifting objects. Rarely, the muscles of breathing may be affected. Weakness of themuscles used for swallowing can cause difficulty with swallowing (dysphagia). Joint pain and/or swelling also may be present. Later in the course of these diseases, muscle wasting or shortening (contracture) may develop in the arms or legs. Heart abnormalities, including electrocardiogram (ECG) changes and arrhythmias, develop at some time during the coursed of these diseases in about 30% of patients.
Dermatomyositis is marked by a skin rash. The rash is dusky, reddish, or lilac in color, and is most often seen on the eyelids, cheeks, bridge of the nose, and knuckles, as well as on the back, upper chest, knees, and elbows. The rash often appears before the muscle weakness.
PM and DM are often difficult diseases to diagnose, because they are rare, because symptoms come on slowly, and because they can be mistaken for other diseases that cause muscle weakness, especially limb girdle muscular dystrophy.
Accurate diagnosis involves:
- A neurological exam.
- Blood tests to determine the level of the muscle enzyme creatine kinase, whose presence in the circulation indicates muscle damage.
- Electromyography, an electrical test of muscle function.
- Muscle biopsy, in which a small sample of affected muscle is surgically removed for microscopic analysis. A biopsy revealing muscle cells surrounded by immune system cells is a strong indicator of myositis.
PM and DM respond to high doses of immunosuppressant drugs in most cases. The most common medication used is the corticosteroid prednisone. Prednisone therapy usually leads to improvement within two or three months, at which point the dose can be tapered to a lower level to avoid the significant side effects associated with high doses of prednisone. Unresponsive patients are often given a replacement or supplementary immunosuppressant, such as azathioprine, cyclosporine, or methotrexate. Intravenous immunoglobulin treatments may help some people who are unresponsive to other immunosuppressants.
Pain can usually be controlled with an over-the-counter analgesic, such as aspirin, ibuprofen, or naproxen. A speech-language therapist can help suggest exercises and tips to improve difficulty in swallowing. Avoiding weight gain helps prevent overtaxing weakened muscles.
As with all autoimmune conditions, food allergies/intolerances and environmental triggers may be contributing factors. For food allergies and intolerances, an elimination challenge diet can be used under the supervision of a trained practitioner, naturopath, or nutritionist, to identify trigger foods. These foods can then be eliminated from the person's diet. For environmental triggers, it is helpful to identify the source so that it can be avoided or eliminated. A thorough detoxification program can help alleviate symptoms and change the course of the disease. Dietary changes from processed foods to whole foods that do not include allergen triggers can have significant results. Nutrient supplements, especially the antioxidants zinc, selenium, and vitamins A, C, and E, can be beneficial. Constitutional homeopathic treatment can work at a deep level to rebalance the whole person. Acupuncture and Chinese herbs can be effective in symptom alleviation and deep healing. Visualization, guided imagery, and hypnosis for pain management are also useful.
The progression of PM and DM varies considerably from person to person. Immunosuppressants can improve strength, although not all patients respond, and relapses may occur. PM and DM can lead to increasing weakness and disability, although the life span usually is not significantly affected. About half of the patients recover and can discontinue treatment within five years of the onset of their symptoms. About 20% still have active disease requiring ongoing treatment after five years, and about 30% have inactive disease but some remaining muscle weakness.
There is no known way to prevent myositis, except to avoid exposure to those environmental agents that may be associated with some cases.
Dermatomyositis and Polymyositis Support Group. 146 Newtown Road, Southampton, SO2 9HR, U.K.
Myositis Association of America. 600-D University Boulevard, Harrisonburg, VA 22801. (540) 433-7686. 〈http://www.myositis.org〉.
National Institutes of Health. National Institute of Arthritis and Musculoskeletal and Skin Diseases. 900 Rockville Pike, Bethesda, MD 20892. (301) 496-8188. 〈http://www.hih.gov.niams〉.
Autoimmune disease— A diseases in which the body's immune system, responsible for fighting off foreign invaders such as bacteria and viruses, begins to attack and damage a part of the body as if it were foreign.
Immunosuppressant— A drug that reduces the body's natural immunity by suppressing the natural functioning of the immune system.
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Robinson, Richard. "Polymyositis." Gale Encyclopedia of Medicine, 3rd ed.. 2006. Retrieved May 27, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3451601291.html
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"polymyositis." A Dictionary of Nursing. 2008. Retrieved May 27, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O62-polymyositis.html