MDA leads the search for treatments and therapies for polymyositis (PM). The Association also provides comprehensive supports and expert clinical care for those living with PM.
In this section, you’ll find up-to-date information about polymyositis, as well as many helpful resources. This information has been compiled with input from researchers, physicians and people affected by the disease.
As you learn more about PM, always remember that you’re not alone. MDA is here for you and your family, standing ready to provide help and hope. There is a place for you in the MDA PM community.
MDA provides support by:
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In addition, MDA will keep you informed through e-alerts, educational publications and speakers, seminars, videos and newsletters.
Please know that there’s a role for you in the fight against polymyositis. The MDA community is strong and dedicated, with opportunities for involvement at all levels, such as:
Please know that there’s an important role for every member of the PM community. We urge you to contact your local MDA office  to learn more.
A PM diagnosis doesn’t mean an end to your hopes and dreams. Changes, challenges and adaptations lay ahead, but also opportunity, fulfillment, joy and hope for a future free of polymyositis.
Never forget that MDA is here to help.
|Polymyositis mostly affects the muscles of the hips and thighs, the upper arms, the top part of the back, the shoulder area and the neck.|
Polymyositis is one of the inflammatory myopathies, a group of muscle diseases that involves inflammation of the muscles or associated tissues, such as the blood vessels that supply the muscles. A myopathy is a muscle disease, and inflammation is response to cell damage.
Another word for inflammatory myopathy is myositis. The myo root means muscle, and the itis root means inflammation; so a myositis is an inflammatory muscle disease.
The muscles of the shoulders, upper arms, hips, thighs and neck display the most weakness in PM. There also can be pain or tenderness in the affected areas, as well as swallowing problems and inflammation of the heart and lung muscle tissues. For more, see Signs and Symptoms .
In most cases, the cause of an inflammatory myopathy is unclear. For some reason, the body’s immune system turns against its own muscles and damages muscle tissue in an autoimmune process. In PM, the inflammatory cells of the immune system directly attack muscle fibers.
PM is not a genetic disorder, although there may be genetic factors that make it more or less likely that an inflammatory myopathy will develop. For more, see Causes/Inheritance .
PM usually begins after age 20, and its progression is gradual. Although inflammatory myopathies like PM can lead to great discomfort for at least a period of time, effective treatments are available, and for the most part these conditions aren’t life-threatening. In fact, many people recover partially or completely from PM.
New research is rapidly leading to increased understanding of PM and to more successful treatments. Scientists are examining factors that may trigger PM such as viruses, certain drugs or vaccines. All these factors are being studied so inflammatory myopathies like PM can someday be better understood, treated or perhaps prevented entirely. For more, see Research .
Polymyositis (PM) is more common in females than males and usually begins after age 20. Over a period of weeks or months, several muscles become weak and gradually get weaker. Most affected are the muscles of the hips and thighs, the upper arms, the top part of the back, the shoulder area and the muscles that move the neck.
Many people with PM have pain or tenderness in the affected areas. The person may have trouble extending the knee, stepping down or climbing stairs.
Lifting things, fixing the hair or putting things on a high shelf may be difficult. It can be hard to raise the head off the bed when lying down.
PM also can affect the heart muscle, causing a condition called inflammatory cardiomyopathy. The muscles involved in breathing may be affected and a few people develop some inflammation of the lung tissues themselves, another respiratory complication.
Of course, the heart, respiratory and swallowing problems are the most serious effects of PM and need close monitoring.
As with other muscle diseases, a doctor diagnoses polymyositis (PM) by considering an individual’s history, family medical history and the results of a careful physical examination. This may be followed by some lab tests, perhaps of the electrical activity inside the muscles and usually a muscle biopsy.
After a careful history and physical exam to document the pattern of weakness in muscles, a doctor who suspects myositis likely will order a blood test to check the level of creatine kinase (CK) , an enzyme that leaks out of muscle fibers when the fibers are being damaged. In PM, the CK level is usually very high.
In some cases, the doctor may ask for a blood test for specific antibodies, proteins produced by the immune system in myositis and other autoimmune diseases. Some of these antibodies appear to be specific to autoimmune muscle disease.
The next step is sometimes an electromyogram , a test in which tiny needles are inserted into the muscles to test their electrical activity both at rest and when the person tries to contract the muscle.
Inflammatory myopathies show a distinctive pattern of electrical activity that can help differentiate them from other types of muscle disease.
A nerve conduction velocity test is sometimes performed. This test measures how fast a nerve impulse travels and how strong it is.
Sometimes these tests are used to rule out disorders that may mimic the symptoms of inflammatory myopathies.
A person with a suspected inflammatory myopathy is often asked to undergo a muscle biopsy , a procedure in which a small piece of muscle is removed for examination. This biopsy can enable the physician to pinpoint the diagnosis to a type of myositis.
In PM, the biopsy generally shows the muscle fibers themselves being invaded by cells of the immune system.
In most cases, the cause of an inflammatory myopathy like polymyositis (PM) is unclear. For some reason, the body’s immune system turns against its own muscles and damages muscle tissue in an autoimmune process.
Viruses might be a trigger for autoimmune myositis. People with the HIV virus, which causes AIDS, can develop a myositis, as can people with a virus called HTLV-1. Some myositis cases have followed infection with the Coxsackie B virus.
There are reports of myositis following exposure to certain drugs. Among the drugs that have been suspected of contributing to myositis are carticaine (a local anesthetic), penicillamine (a drug used to lower copper levels in the body), interferon-alpha (mostly used to treat cancer and hepatitis), cimetidine (used to treat ulcers), carbimazole (to treat thyroid disease), phenytoin (used to treat seizures) and growth hormone. The vaccine for hepatitis B also has been implicated in some cases.
Recent research suggests that the mixing of blood cells of a mother and a fetus during pregnancy could lead to the later development of an autoimmune disease such as myositis in the mother or the child.
Although inflammatory myopathies like PM aren’t genetic, there may be genetic factors that make it more or less likely that an inflammatory myopathy will develop.
Polymyositis (PM) is a highly treatable disease. Some people recover completely, while others experience greatly diminished symptoms for long periods of time. Several years of treatment to suppress the immune system may be necessary to achieve these results.
Those who don’t recover completely may need to continue on at least a low dose of medication to control the autoimmune attack of PM throughout their lives.
Drugs that suppress the immune system are the mainstay of therapy for PM. The chart  below describes the drugs and treatments commonly used in PM, how they work and their side effects.
The first drug used in the treatment of PM is usually a corticosteroid, such as prednisone. The treatment may involve high-dose oral prednisone on a daily, every other day, or other schedule; or intermittent, short courses of intravenous corticosteroids. Sometimes, prednisone is stopped and then has to be restarted several times during the course of the disease. Prednisone is usually very effective at bringing inflammation under control, restoring for the most part the person’s strength, as well as swallowing, breathing and heart functions.
But prednisone can have many side effects, including unwanted weight gain, redistribution of fat to the face and abdomen and away from the limbs, thinning of the skin, bone loss, cataracts and psychological problems. For this reason, if long-term treatment is necessary, most doctors (and patients) want to lower the dose of prednisone as quickly as possible. This can be accomplished by adding one or more other medications to suppress the damage being caused by the immune system.
These medications include azathioprine, methotrexate, cyclosporine, cyclophosphamide — all “traditional” immunosuppressants that have been used for many years; and some newer drugs, such as mycophenolate mofetil and tacrolimus.
Although most people tolerate these medications without difficulty, they carry their own risks, such as flulike symptoms, a lowered white blood cell count (which can predispose the patient to infection) and liver toxicity. Many are associated with an increased risk of cancer.
Some with PM have responded well to intravenous infusion of antibodies culled from donors. This treatment — known as intravenous immunoglobulins, or IVIg, may seem strange in a disease that’s probably caused by an immune response in the first place, but the extra antibodies seem to “confuse” the immune system and at least temporarily alleviate the attack on muscle.
Gently progressive physical therapy, such as that taken in a swimming pool, can be very helpful in maintaining strength. Range-of-motion exercise (putting a joint through its normal movement range), particularly of the shoulders, is helpful in keeping the joints supple.
Some people may need a cane, walker or even a wheelchair during acute flare-ups of PM.
Many people eventually recover much or all of their muscle strength and function, although they may relapse and lose function if they stop taking medications.
Plasmapheresis, a “blood-cleansing” process to remove antibodies, was at one time used in PM but is rarely used today. Immunosuppressant drugs and/or IVIg treatments are now considered more effective.
|Medication or treatment||How it works||Comments|
corticosteroids prednisone tablets (Deltasone);
intravenous methylprednisolone sodium succinate
|Dampens inflammation and immune response by interfering with processing of antigens and with early triggering of T cell and B cell production and later proliferation of B cells and T cells. These cells are produced by the immune system in autoimmune diseases such as PM and DM.||Can be taken orally as prednisone and related compounds; also available for intravenous use. Many side effects with long-term, high-dose therapy, such as weight gain and redistribution of fat to face, abdomen and upper back; thinning of skin; susceptibility to infection; bone loss; muscle damage; cataracts; elevated pressures in eyes (glaucoma); psychological disturbances; high blood pressure; high blood sugar; growth slowing in children.|
|Interferes with proliferation of B cells and T cells.||Can suppress production of several types of blood cells, so cell counts must be monitored; increases risk of cancer.|
|methotrexate (Rheumatrex, Folex, Mexate)||Interferes with proliferation of B cells and T cells.||Can cause liver damage; used in higher doses to treat cancer.|
|Keeps T cells from stimulating production of more T cells and B cells (“upstream” of azathioprine and methotrexate action).||Doesn’t affect production of cells other than T cells and B cells; can cause kidney damage, infection, high blood pressure, tremor and excessive hair growth.|
|Interferes with proliferation and activity of B cells and T cells||Also used in cancer; toxic to many kinds of cells, including those of the blood and bladder; can cause sterility in both sexes.|
|Interferes with proliferation of B cells and T cells.||Can cause diarrhea, vomiting, infection (particularly with cytomegalovirus); increases risk of cancer, especially lymphomas; causes depletion of certain blood cells.|
|tacrolimus (Prograf, old name FK506)||Keeps T cells from stimulating production of more T cells and B cells (“upstream” of azathioprine and methotrexate action).||Can damage kidneys; can cause headaches, tremors and sleep difficulties; diarrhea, nausea and vomiting; high blood pressure, high blood sugar and high blood levels of potassium; increases risk of infection and lymphomas. Drug breakdown interfered with by grapefruit juice; potential for kidney damage increased by some anti-inflammatory drugs.|
|Mechanism not understood; used in arthritis, lupus, malaria; can be used to reduce steroid dosage in myositis, particularly in children.||Can treat muscle symptoms and dermatomyositis rash; can cause damage to eyes’ retinas or corneas; regular eye exams needed.|
infusion of mixed
(Gammar, Gammagard, Sandoglobulin others)
|Has complex actions on immune system, such as providing antibodies against patient’s own antibodies; interfering with immune system reaction to antibody-marked cells; interfering with blood-transported chemicals released by immune system; interfering with activation and maturation of T cells and B cells.||Doesn’t affect production of cells other than T cells and B cells; can cause kidney damage, infection, high blood pressure, tremor and excessive hair growth.|
|plasmapheresis||Removes antibodies and proteins made by the immune system from the blood and returns “cleansed” blood to patient.||Very rarely used in myositis since 1992 study showed it was no more effective than placebo; some think it’s useful when combined with immunosuppressant drugs.|
MDA-supported scientists are studying the underlying mechanisms that cause inflammatory myopathies, the group of diseases to which polymyositis (PM) belongs. Understanding precisely why and how the immune system attacks muscle tissue in PM will likely lead to better treatments for the disease.
One research team is studying inflammatory myopathies in dogs. These diseases appear to be similar in dogs and humans, and it is believed that this project may generate deeper understanding of human PM, and lead to new tools for diagnosis and treatment.
In addition, many clinical trials  are being conducted in PM.
For more about research in and medical management of PM, see:
A clinical trial is a test in humans of an experimental medication or therapy. Clinical trials are experiments, not treatments, and participation requires careful consideration.
Although it's possible to benefit from participating in a clinical trial, it's also possible that no benefit — or even harm — may occur. Keep your MDA clinic  doctor informed about any clinical trial participation. (Note that MDA has no ability to influence who is chosen to participate in a clinical trial.)
For a more refined list of PM clinical trials, visit ClinicalTrials.gov , a registry of federally and privately supported clinical trials in the United States and around the world. Select "Search for Clinical Trials," and follow the instructions to narrow down your search results.