Basics of myositis

Myositis is the term for illnesses that involve chronic muscle inflammation ("myo" means muscle and "itis" means inflammation).

"Myositis" refers to several different illnesses including polymyositis, dermatomyositis and inclusion body myositis.

All forms of myositis involve chronic or persistent muscle inflammation. This muscle inflammation almost always results in weakness and less often in heat swelling and pain of the muscles. Myositis can affect many parts of the body. Sometimes the joints heart lungs intestines and skin can become inflamed.

Some forms of myositis like dermatomyositis ("dermato" refers to the skin) result in particular rashes over the knuckles around the eyes or sometimes in other parts of the body. Other forms of myositis occur in children. Some forms are seen with other connective tissues diseases like lupus or rheumatoid arthritis. Still other forms may occur in people with tumors. Rarely myositis can occur in a single part of the body such as one arm, one leg or just the muscles that move the eye.


Like other rheumatic diseases, myositis is unlikely to go away on its own. But with proper treatment and management these chronic diseases can be brought under control.


At present there is no cure for myositis. A person with myositis will need to manage the condition and to adjust to the changes it brings. This may involve continuing to take medicine and seeing a doctor regularly. It may also require changing some activities especially during periods of increased pain and weakness. For most people with myositis however treatment of myositis is satisfactory and they can lead productive lives. Myositis is more serious if it affects the breathing muscles the heart is combined with a tumor or if certain autoantibodies are present. People with these complications will need to be monitored even more closely by their doctors.


Myositis is a rare disease. In the United States it is estimated that each year five to 10 out of every one million people get one of the forms of myositis.

Although myositis can affect people of any age most children who get the disease are between five and 15 years of age and most adults are between 30 and 60. Like many other inflammatory diseases most forms of myositis attack more women than men. The exception is inclusion body myositis a form of myositis in which holes called inclusion bodies develop in the muscle fibers. This form affects more men than women.


We do not know what causes myositis. But because myositis has many forms it probably has many causes. Some scientists think that myositis results when a person with a certain genetic background is exposed to particular chemicals viruses or other infectious agents.

Whatever triggers these diseases also results in abnormalities in the immune system. The immune system consists of groups of cells called lymphocytes that circulate throughout the body. In healthy people these lymphocytes act as a defense force that produces substances that attack viruses bacteria and other agents of disease. But in many people with myositis there is an abnormality in the immune system that results in the production of proteins called autoantibodies. Autoantibodies and some of the lymphocytes turn against the body's own tissues and may cause damage.

Because illnesses associated with autoantibodies are called autoimmune diseases many doctors consider myositis to be an autoimmune disease. Some autoantibodies found in people with myositis are found in other autoimmune diseases but a few special ones are only found in people with myositis. These are called myositis-specific autoantibodies. They seem to be useful in helping doctors predict the problems that some people might develop and how they might respond to treatment.


Because myositis closely resembles many other diseases and differs so much from person to person it can be difficult to diagnose.

Your doctor may have to perform many tests and see you many times before deciding on a diagnosis of myositis. It often is necessary for your primary care doctor to send you to an arthritis specialist. Consultation with a neurologist who specializes in disorders of the nervous system may also be indicated.

During the process of reaching a diagnosis your doctor will ask a series of questions about the problems you are experiencing and will perform a physical examination. There are blood tests that may be done including some for autoantibodies and muscle enzymes. One of the most useful is a blood test for a muscle enzyme called creatine kinase or CK. In most people with active myositis the CK level in the blood is abnormally high. The CK level tends to go up with increasing myositis disease activity and tends to go down as the myositis improves.

Another procedure very useful in diagnosing myositis is an electromyogram (EMG). An EMG measures the electrical pattern of the muscles just as an electrocardiogram (EKG) measures the electrical pattern of the heart.

Your doctor will probably also request that a muscle biopsy be done. This is the removal of a small piece of muscle for staining and examination with a microscope. The muscle biopsy shows your doctor whether and how the muscle fibers are damaged.


There are many forms of treatment for myositis but most include medications, exercise physical therapy and rest.

The treatment will vary from person to person and will change over time in a single person. The specific therapy recommended by your doctor will depend upon the severity and type of problems the presence of other medical conditions and adverse reactions to previous therapy.

Exercise and therapy

A physical therapy or exercise program is an important part of treating myositis and can help improve muscle strength. However you should not begin vigorous exercise until the drug treatment takes effect. In the early stages of treating myositis your muscle fibers are fragile and could be damaged further by such exercises. Physical examination and laboratory tests will help your doctor determine the appropriate time to start an exercise program.

But even when strenuous exercise is not recommended it is important to prevent loss of flexibility of your arms legs and other parts of your body by doing range of motion stretching of the joints and muscles. Other physical therapy activities may range from simple exercises at home to formal sessions with a specially trained health professional. They can also include whirlpool baths heat and gentle massage or similar therapies. As you get better your physical therapy program will be adjusted accordingly with more vigorous exercises. Exercising in pools can be very helpful in restoring your muscle function to normal.

Getting adequate rest is another important aspect of managing myositis. During times of increased muscle weakness you need to take frequent rests during the day and to limit your activity to a tolerable level. If you are employed you need to discuss your situation with coworkers, supervisors and your doctors to develop a work plan to accommodate your disease. When your myositis is active you should minimize strong physical activity and your workday should include rest breaks. More activity can be undertaken and fewer rest breaks will be needed as your condition improves but you need to avoid overdoing activity at the first sign of improvement. Your doctor and physical therapist can help decide the proper balance of rest and activity at each stage of myositis.



The most effective drugs in treating myositis are corticosteroids. These drugs are related to hormones produced naturally in the body. Corticosteroids are powerful and can have serious side effects. Some of these side effects include:

  • weight gain
  • rounding of the face
  • easy bruising
  • thinning of the bones
  • depression
  • high blood pressure
  • cataracts
  • diabetes
  • increased risk of infection
  • rarely bleeding from the stomach
  • avascular necrosis an arthritis like condition that most commonly affects the hips or shoulders and can be treated with total hip replacement or total shoulder replacement

If you take corticosteroids, you should be monitored carefully by your doctor and should report any new medical problems to the doctor.

Anyone taking corticosteroids should be aware of several precautions. During such therapy the body slows or stops its own natural production of steroids. For this reason any time the dose is to be lowered your doctor will gradually reduce the level of steroids you are taking over a period of weeks or months. During this time your body will gradually increase its own corticosteroid production. Do not ever decide on your own to stop or drastically reduce the amount of prednisone or other corticosteroid you are taking even if you feel well. Serious health problems could result if you do! You may want to wear a medic alert bracelet that says you are taking corticosteroids.

If you have taken corticosteroids for a long time be sure to discuss your medications with all doctors and dentists treating you. Any situation that places extra stress on your body such as surgery or major dental work may require higher levels of corticosteroids than you will be able to produce. This may require that the corticosteroid dosage be increased temporarily during such stressful periods.

The corticosteroid most commonly used for myositis is prednisone. If your myositis is severe your doctor may prescribe fairly high doses of corticosteroids. This may be done by giving prednisone as pills to be taken by mouth or in liquid form given through a plastic tube that enters a vein (intravenously). It may take several weeks or months for you to notice improvement even though you may be getting better without realizing it. Throughout the treatment of myositis your doctor will repeat blood tests for muscle enzymes to watch for signs of progress. Often the CK muscle enzyme will begin returning to normal before you notice any improvement.

After your strength improves your doctor probably will begin slowly reducing the dose of prednisone to a lower level that may remain the same for a long period of time. If your myositis is under good control your doctor may eventually be able to take you off prednisone completely at least for a time.


You may not respond to prednisone therapy alone. Your doctor may then prescribe both prednisone and a drug that suppresses the immune system. Such drugs are called immunosuppressants and the most common ones used in myositis are methotrexate and azathioprine. Immunosuppressants slow down the immune system reducing its ability to attack infections and attack healthy tissue in persons with autoimmune disease.

Immunosuppressant drugs are powerful agents and can result in side effects. If you are taking these medications see your doctor regularly so that he or she can check for any side effects and decrease the dosage of medicine if necessary. Your doctor may request ongoing consultation with a arthritis specialist when your treatment includes the use of immunosuppressant drugs.

If any of these side effects occur contact your doctor

  • upset stomach
  • loss of appetite
  • mouth sores
  • hair loss
  • skin rash
  • fever
  • chills
  • blood in urine
  • diarrhea
  • missed menstrual periods

Caution: Methotrexate may cause birth defects. Women on methotrexate must go off their medication during pregnancy and for several months prior to a planned pregnancy! Methotrexate should not be taken by people who have serious kidney or liver disease or who drink alcohol.

Condition research

Researchers are making some progress in understanding what happens in myositis and what goes wrong with the immune system. Currently they believe that the muscle fibers in some people with myositis are damaged by a group of cells called lymphocytes which make up part of the immune system. Researchers also are studying the possibility that certain autoantibodies may travel through the blood and cause damage to the muscle. Other researchers are studying how many different forms of myositis exist and how they are different from one another in their cause and treatment.

As scientists get closer to understanding the process leading to muscle damage in the different forms of myositis they can hope to find new ways of stopping the harmful actions. With the scientific progress that has been made in recent years people with myositis have reason to share that hope.

Research holds the key to better ways to prevent diagnose and control myositis.


Some of this material may also be available in an Arthritis Foundation brochure. 

Adapted from the pamphlet originally prepared for the Arthritis Foundation by Frederick W. Miller M.D. Ph.D. This material is protected by copyright.

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