Polymyositis (PM) and Dermatomyositis (DM) are two similar and rare chronic (long-term) diseases that affect the muscles. They cause inflammation in the muscles that leads to weakness but not usually pain or swelling. The most significant difference between PM and DM in terms of symptoms is that a rash also occurs with DM that does not occur with PM.
When polymyositis and dermatomyositis are severe, they can cause problems with things like swallowing. This is serious because it can cause a person to choke or breathe things into their lungs. In the rarest and worst of cases, it can even impact the muscle of the heart and the muscles used for breathing.
PM and DM are autoimmune diseases, meaning that they occur when the body’s immune system attacks its own healthy cells and tissues. The reason why it does this is not well understood. When the body’s immune system is “activated” in this way, it can make a person feel very tired, similar to when they have the flu.
PM and DM are types of inflammatory myopathies, which refer to diseases that cause inflammation of the muscles.
For simplicity, this article will refer to them as myositis. There are other types of myositis that are not related to the autoimmune disorders PM and DM discussed in this article.
Myositis can exist on its own, or it can sometimes be seen along with other rheumatic diseases. Muscle inflammation can be seen with Sjogren’s syndrome, lupus, and systemic sclerosis (scleroderma). In a small number of people, myositis can be accompanied by a cancer that somehow triggers the immune system and causes the condition. Everybody who gets myositis should be screened for cancer.
While anyone can get PM or DM, they most often affect two age groups: children aged 10 to 15 and adults aged 45 to 60. Myositis is very rare: it affects only about 10 people in every million. Women are about 2 times more likely to get myositis than men.
One of the first things people with myositis notice is fatigue. Muscle weakness comes on slowly over time.
It can take a while before a person notices the muscle weakness since it happens gradually, usually over several months. People with myositis might start to have trouble getting up from a chair, climbing the stairs, getting up off the floor, or lifting things above their head.
When myositis is more severe, it can cause problems with things like swallowing. This is serious because it can cause a person to choke or breathe things into their lungs.
In the rarest and worst of cases, myositis can cause weakness in the heart muscle and the muscles that enable breathing.
In some people with myositis, inflammation can be seen in other places. One of the most common places it can affect after the muscles are the joints, leading to pain and stiffness (arthritis). The stiffness is usually worse in the morning or after a period of rest. In some people, it gets better once the joints have had a chance to get “worked out.”
Myositis can cause weight loss. People with the disease can lose weight because of a loss of appetite or from the disease itself.
If myositis causes inflammation in the lungs it can lead to shortness of breath. It can also rarely cause pain with a deep breath.
Rash (Dermatomyositis Only)
People who have dermatomyositis get a rash. In some cases, the rash happens up to 1 year before the muscle weakness comes on. The rash can occur in several different spots, but the most common ones are:
- Backs of the hands or over the knuckles
- Chest (the rash often forms a “V” shape)
- Shoulders (like a shawl)
- Face and forehead
Some people with myositis may also develop swelling around the eyes.
They can also develop a condition called Raynaud’s phenomenon. This causes the fingers and toes to turn white and discolour after exposure to cold.
Myositis is best diagnosed by someone who is very familiar with the condition. This is usually a rheumatologist, a type of doctor that is an expert in autoimmune disease and arthritis, or a neurologist, a type of doctor that is an expert in the nervous system.
The doctor will take a thorough history and will then perform a complete physical examination. Following this various tests will be arranged to confirm PM or DM and to rule out other possible conditions.
Other causes of inflammation in the muscles that are not related to myositis include: certain medications and drugs, hormone imbalances (thyroid, cortisone), infections, and rare genetic conditions.
If a diagnosis of PM or DM is confirmed in a patient, they should be screened for cancer as well.
Common Tests to Diagnose Myositis
Looking for high levels of muscle enzymes: The first type of blood tests look for high levels of muscle enzymes in the blood. When the muscles are inflamed they become damaged and break down. The enzymes inside the muscles then “leak out” into the blood. The levels of these enzymes can be measured with a blood test.
The most common enzyme measured is called Creatinine Kinase (CK). CK is often very elevated in people with myositis, ranging from the 1000’s to 10,000’s. In 5% of patients the CK can actually be normal.
Other muscle enzymes including AST, ALT, LDH, and aldolase can also be measured. These are also often elevated.
Looking for antibodies against muscles: The second type of blood tests look to see if the body is producing antibodies against the muscles. Common antibodies tested for include Anti-Nuclear Antibody (ANA) Test and the Extractable Nuclear Antigen (ENA) Panel.
Looking for muscle inflammation: An Electromyography (EMG) test can determine whether the muscles are inflamed (which could be PM or DM) or if there is something else causing them to break down and weaken. During an EMG test, small needles are inserted to test the muscles.
Looking for findings (or signs) of PM or DM: The best test to ultimately confirm a diagnosis of PM or DM is a muscle biopsy. This is a type of operation where a surgeon removes a small piece of muscle tissue to be examined in a lab. If the patient has PM or DM, common findings, or signs, consistent with these diseases will be seen in the tissue sample.
Common Tests to Screen for Cancer
Everyone with myositis should be screened for cancer because in a small number of patients, their myositis is accompanied by cancer. Patients should tell their doctor if they have a first degree relative (e.g. mom, dad, brother, or sister) that has ever had cancer. Common tests for cancer include:
- CT scan of Chest, Abdomen, and Pelvis
- Mammogram for women
- Prostate exam and PSA blood test for men
- Pap smear for women
- Ca 125 (cancer antigen 25) blood testing for women
- Stool testing to look for blood and a colonoscopy
- Thyroid ultrasound and thyroid testing
Scientists don’t know exactly what causes the immune system to start attacking the muscles in polymyositis or dermatomyositis, or why some people develop these diseases but others don’t.
In rarer cases, PM or DM may be accompanied by cancer. The cancer somehow triggers the immune system in a way that causes the myositis.
Treatment of myositis usually involves both medications and physical therapy. It is very important to treat myositis as early and aggressively as possible to prevent severe muscle damage and ensure the best possible treatment outcome.
In rarer cases where myositis is accompanied by cancer, treating the cancer often helps the myositis. It is very important to treat the myositis as well as the cancer.
Prednisone is the main medication used to treat myositis. It is a powerful medication that helps control the immune system and its attack on the muscles. It is usually started at high doses that will usually be tapered (lowered over time).
Disease Modifying Anti-Rheumatic Drugs (DMARDs)
The DMARDs that treat other types of arthritis can be effective in treating myositis. Methotrexate and Imuran (azathioprine) are common choices that are often combined with prednisone to get the disease under control quickly. DMARD medications can sometimes take a few months before patients start to notice improvements.
Intravenous Immunoglobulin (IVIG)
IVIG is sometimes used in people with severe myositis. This drug doesn’t work in everyone, but when it does work for someone, it can work extremely well.
Physical Therapy and Exercise
Physical therapy and exercise are important treatments to rebuild and to regain strength, flexibility, and range of motion. The right stretching and exercises can also reduce fatigue and emotional distress caused by myositis, and are most effective when done daily.
A trained arthritis physiotherapist can help design an exercise program that helps return muscles to their former strength. The earlier patients start this type of therapy, the better the results.
Everyone with myositis should be screened for cancer because for a small number of patients, their myositis can be related to cancer.
In these cases, cancer somehow turns on the immune system and causes the myositis. When this happens, treating the cancer often helps the myositis.
Patients with myositis should tell their doctor if they have a first degree relative (mom, dad, brother, or sister) that has had cancer.
Living with PM
The pain and stiffness caused by PM can sometimes limit people’s normal activities, including work. There are many things people can do to lessen the impact of PM on their work and daily routine.
We recommend adjusting features of the workplace to help make working with PM easier. For example, people that sit for much of the day can adjust the position of chairs and desks for proper posture. Vehicle seats can be adjusted to make driving more comfortable and reduce stress on joints and affected tissues.
Those who find out they have PM while they’re still young can consider choosing work that isn’t physically demanding on their joints and back.
Exercise is important to overall health. It also helps keep the joints moving properly, and helps protect them by strengthening the muscles around them.
The level and amount of exercise people with PM can do depends on the activity of their disease.
A trained arthritis physiotherapist is the best person to help design an exercise program tailored to the needs of patients with PM.
The following are some useful articles on exercising with arthritis:
Exercise and Arthritis: An article by arthritis physiotherapist Marlene Thompson
Exercising in a Flare: Another excellent article by Marlene Thompson on how to cope with flares through your exercise routine.
Alcoholic beverages are not an effective treatment for PM, and they can interact with many medications.
People with PM that plan on drinking should ask their doctor about possible negative interactions with the medications they take.
Some examples of medication that mixes poorly with alcohol includes, and is not limited to: the DMARDs methotrexate, Arava (leflunomide), and Imuran (azathioprine).
Smoking is not healthy for people with PM. It can make symptoms worse and harder to treat.
Research has shown that some arthritis medications do not work as well in people who smoke.
We recommend that smokers quit immediately to reduce the impact of their symptoms, improve the effectiveness of their medications, and improve their overall health.
Smoking significantly increases the risk of cardiovascular disease. The chronic (long-term) inflammation caused by rheumatic diseases like PM already increases this risk without a big extra boost from smoking.
Travel is still possible when you have PM.
It is best for people with this disease to get organized well in advance of a trip to ensure a smooth, comfortable, and enjoyable time.
Check out our Travel Checklist page.
Though PM does not particularly cause a loss of sex drive, it can cause pain, fatigue and emotional hardships. These hardships risk creating barriers to sexual needs, ability, and satisfaction.
People with PM can take comfort knowing that sex and intimacy can be maintained. In many cases, it can help draw partners closer together, especially through improved communication.
For more information on intimacy and arthritis, a great book is: Rheumatoid Arthritis: Plan to Win by Cheryl Koehn, Taysha Palmer and John Esdaile.
Polymyositis (PM) has no effect on fertility. The chances of getting pregnant for people with PM are the same as with people that don’t have it. PM also has no known effects on the developing fetus or the newborn.
The two main issues doctors worry about with PM and pregnancy are:
Patients with PM might be treated with a number of medications that can affect pregancies including NSAIDs, anti-TNF biologics, and occasionally DMARDs. It is important for people with PM who want to become pregnant to discuss their medications with their doctor and create a pre-pregnancy plan. A plan is important for a number of reasons. For example, discontinuing a particular medication for safety of the newborn might cause PM to flare, so its wise to have a plan in place to handle these possibilities.
Any type of arthritis that affects the pelvis or the hips can make vaginal delivery difficult. It is important for those planning pregnancy to discuss delivery options with an obstetrician.
Following the basics of healthy eating can help improve health and well-being in everyone, including those with PM. Keeping a healthy weight helps reduce the load on weight-bearing joints including the spine, hips, and knees, making it easier to live with the disease.
Unfortuantely, no special diet has ever been proven to significantly alter the course of PM or any other types of arthritis.
In addition, no known natural remedies or complementary therapies have been proven to help PM in any significant way.
People with PM should consult with their doctor to make sure that any supplements or alternative therapies they consume will not negatively interact with their medications.
Its very important for people with PM to attend regularly scheduled appointments with their rheumatologist, and promptly get any tests that are ordered by their doctors.
It is often very important that medications are taken exactly as prescribed. Patients should always talk to their doctor about any issues they experience, or if they would like to change anything.
Polymyositis is a chronic disease and a rheumatologist is the best partner in helping patients achieve the best quality of life possible.