Polymyositis and Dermatomyositis
An Information BooklET
Introduction
Inflammation of the muscles is called myositis (myo = muscle, sitis = inflammation). Polymyositis is a condition which affects many muscles (poly = many), mainly the larger muscles of the body, such as those around the shoulders, hips and thighs. This booklet also deals with dermatomyositis. This is a disease where a particular skin rash occurs (derm = skin) with muscle inflammation that is similar to polymyositis.
This booklet explains:
- the nature of these conditions and the importance of getting proper treatment
- who is affected
- the probable causes of the conditions
- how doctors diagnose them and the tests used to do this
- treatments and possible side-effects of drug therapies
- current research into the conditions.
It also includes questions often raised by people who have polymyositis or dermatomyositis. Finally it gives useful addresses for further information.
What are the symptoms of polymyositis and dermatomyositis?
Polymyositis affects mainly the large muscles of the body, such as those around the shoulders, hips and thighs. If you suffer from it you may have difficulty climbing stairs, getting up from low chairs, and getting in and out of the bath. Your muscles may feel weak and very tired, so that tasks that are normally easy are now exhausting for you. You may also feel pain in your muscles, known as myalgia, and your inflamed muscles may be tender to the touch. People with polymyositis may feel generally unwell (malaise) and have weight loss or night sweats.
Figure 1. Muscle weakness can cause difficulty in many daily activities.
However, polymyositis is not always so severe. Symptoms range from mild pain and stiffness (making the condition difficult to diagnose) through to a condition which comes on rapidly with severe weakness becoming apparent within a few days. In a small number of cases polymyositis can become such a serious problem that it affects breathing and swallowing.
Polymyositis can develop in muscles alone or alongside inflammation of other tissues of the body. There can be a red/pink rash on the upper eyelids, face, neck, and backs of the hands and fingers. The affected skin may become swollen – which gives a characteristic puffiness and colouring around the eyes. When myositis occurs with this specific rash the condition is called dermatomyositis.
Polymyositis and dermatomyositis usually affect adults, though there is a type of dermatomyositis which affects children. This is called juvenile dermatomyositis.
Who may be affected?
Polymyositis and dermatomyositis are rare diseases, affecting only 6–8 people out of every 100,000 of the population. People who have symptoms which may be due to polymyositis or dermatomyositis are usually referred to a specialist. This could be a skin specialist (dermatologist) if your rash is the most troublesome symptom, a nerve specialist (neurologist) if muscle weakness is the biggest problem, or a joint and muscle specialist (rheumatologist) if joint or muscle pain is the main issue. Some people need the help of more than one of these specialists.
If the symptoms have appeared very suddenly, and especially if they are accompanied by breathing or swallowing difficulties, you may be admitted urgently into hospital under a general physician.
What causes polymyositis and dermatomyositis?
The processes in the body that cause polymyositis and dermatomyositis are not well understood. Normally, the body's immune system protects it against infections such as those caused by bacteria and viruses. In polymyositis and dermatomyositis the immune system attacks the body's own tissues, causing inflammation in the muscles and possibly the skin.
If small samples of muscle from people with polymyositis and dermatomyositis are examined under a microscope, white blood cells can be seen sticking to the covering of the muscle and damaging the muscle proteins that make the muscle contract. This causes the weakness and fatigue characteristic of myositis.
In the case of dermatomyositis there are also changes in the skin and the small blood vessels which carry the blood to the muscles.
What causes the immune system to turn against the muscles, skin and blood vessels is not known.
How do doctors diagnose the conditions?
Your doctor will ask you to describe your symptoms, and will examine you. Muscle weakness, tiredness and muscle pain can also occur in other conditions and diseases, so you will be asked for a blood sample for testing.
It is especially important to test for levels of muscle enzymes in the blood. These enzymes are substances that are found in muscles and which leak out when the muscles are damaged. One of the most important muscle enzymes is creatine phosphokinase. A high level of creatine phosphokinase in the blood is a very characteristic feature of both polymyositis and dermatomyositis, and the level of this enzyme goes down as the disease is treated. Repeated measurements of this level throughout the course of the disease will help your doctor tell how well your illness is responding to treatment. Another important test is the erythrocyte sedimentation rate (ESR) test, which gives an indication of the level of inflammation.
Further tests will probably be needed, especially as in a minority of cases the results of blood tests are normal. One such test is electromyography (EMG). Normally muscles contract by electrical discharges from nerve endings at muscle membranes, but the electrical properties of the membrane are different in people with myositis. This difference can be detected by inserting a thin electrode probe into the muscle. The pattern of electrical activity is shown on a computer screen. Any alteration produced by myositis will show up. As the effects of myositis are patchy, a number of muscles will need to be tested in this way. These EMG tests are not usually very uncomfortable.
Another test is muscle biopsy. A small sample of muscle, usually taken from the thigh, is examined under a microscope. A local anaesthetic is used to numb the area while the sample is taken, but there may be some discomfort for a day or two afterwards.
What treatments can I have?
Once the diagnosis is confirmed, treatment starts. Steroids are the drugs used as the first choice, and can have a dramatic effect in reducing the inflammation very quickly. An initial, relatively high dose will settle the muscle pain and feeling of being unwell. Muscle strength will take longer to recover, however, as the damage to the muscles may take weeks or sometimes months for the body to repair.
High-dose steroids do have side-effects (see arc leaflet 'Steroid Tablets'). To reduce side-effects, your doctor will only keep the dose high for the shortest possible time. In some cases, the risk of side-effects can be reduced by prescribing other drugs along with the steroids. For example, the risk of developing osteoporosis (thinning of the bones) due to steroids can be reduced with other drugs (see arc booklet 'Osteoporosis').
If the inflammation is so active that it is impossible to reduce the dose of steroids without getting a flare-up of symptoms, then your doctor may add other drugs, which can help the steroids reduce inflammation and thus allow the dose of steroid to be reduced. The two drugs most commonly used are methotrexate and azathioprine (see arc leaflets 'Methotrexate' and 'Azathioprine'). In some cases these drugs may have side-effects of their own, so you will need to have regular blood-monitoring tests to allow your doctors to watch out for signs of these developing.
In a small number of cases tablets alone may not be enough to control the disease and you may require treatment with infusions of immunoglobulins (see arc leaflet 'Intravenous Immunoglobulin'). These are antibodies collected and pooled from blood donations given by healthy people. An infusion of immunoglobulins from healthy people acts to suppress the attack by your immune system on your own tissues. These infusions are given in hospital at monthly or 3-monthly intervals for several months. However, it should be stressed that most people with polymyositis and dermatomyositis do not need treatment with immunoglobulins.
As the disease is controlled, you will be given exercises to counter any muscle wasting. With juvenile dermatomyositis vigorous physiotherapy is needed to make sure that joints, and especially knees, do not become permanently bent – an irreversible change known as a flexion contracture.
What complications of polymyositis and dermatomyositis might occur?
The most frequent complication for adults is that the drug treatment doesn't work, and the muscles stay weak. Research into why drugs do not work for everyone is continuing, but meanwhile it appears that moderate exercise (i.e. not strenuous but sufficient to make you breathe faster) helps the recovery of your muscle strength and improves your ability to use your muscles. Very strenuous exercise should be avoided.
At the start of more severe cases the muscles used for swallowing and breathing may become very weak. People with these conditions may require medical help to eat or breathe.
In both polymyositis and dermatomyositis inflammation of the lung tissues can lead to lung scarring and cause the lungs to work less well. This often irreversible damage can cause long-term breathlessness.
Another complication of myositis is that rarely it can be associated with cancer. Most people with polymyositis and dermatomyositis do not develop cancer but your consultant may well arrange a number of tests to exclude this possibility, e.g. a chest x-ray or an ultrasound scan of your abdomen and pelvis.
Children with dermatomyositis may develop painful calcium deposits in damaged muscles. These, together with the fact that the disease means they spend periods without moving (disease-related immobility), can make them liable to develop permanently bent joints.
What research is being done?
A great deal of research is being done, looking at various aspects of polymyositis and dermatomyositis. Because these conditions are so rare, there is increasing collaboration between research centres. You may hear about such studies. For instance, there is a national clinical study of the effectiveness of steroids in various combinations with other drugs. It aims to establish the best combination of the currently available drugs for treating polymyositis and dermatomyositis. Another example is the UK Adult-Onset Myositis Genetic Collaboration, which has already recruited nearly 400 patients nationally, and is beginning to find out what genetic factors make some people more likely to get myositis. Ultimately this may help us understand the mechanisms responsible for muscle cell damage, and therefore lead to the development of new and more effective treatments. New tests are also being devised to help distinguish myositis from certain other muscle diseases.
Some questions answered
Can I pass myositis on to my children?
Polymyositis and dermatomyositis are not directly inherited (i.e. they are not automatically passed to a child from its parents), although genetic influences clearly play a part. However, if you have polymyositis or dermatomyositis, the chance of your children being affected is very small.
How serious is myositis?
The severity of polymyositis and dermatomyositis can range from mild, producing little weakness, to very extreme, causing breathing difficulties. However, even in severe cases myositis does respond to treatment. It is important to appreciate that, while some people with mild polymyositis and dermatomyositis recover completely and get off all drugs, this is not true for everyone. Many people with more severe inflammation have problems for a long time, and some never fully recover. Ongoing weakness and the associated disability can then be a serious problem.
What is post-infectious reactive myositis?
After some viral infections the body's immune system, after killing the virus, may cause inflammation in parts of the body for a few months. If this occurs in muscle, the result is a short-lived myositis that is called 'post-infectious reactive'. People with this condition develop widespread muscle pain and may get muscle weakness. Some of the tests for polymyositis may show positive, but the condition is usually mild and always settles without the need for specific treatment.
Are there any other types of myositis?
There is a disease called inclusion body myositis (IBM) which is similar to polymyositis and dermatomyositis. People with IBM have the symptoms of muscle weakness, a raised level of the enzyme creatine phosphokinase, and similar muscle biopsy results. It is, however, different in that the weakness most often affects muscles near the ends of the limbs (such as those of the hands, forearms and calves) and symptoms of muscle pain occur only rarely. Although most of the features seen under a microscope in IBM muscle biopsies look like those in polymyositis and dermatomyositis biopsies, we can use very powerful microscopes to see key differences called 'inclusion bodies' inside the muscle cells in IBM. These inclusion bodies are not present in other types of myositis. It is also found that IBM does not respond well to steroids, and this is such a consistent feature that a poor steroid response in somebody who is thought to have polymyositis suggests that further tests may be needed, including a repeat biopsy if necessary.
Is myositis related to fibromyalgia?
Fibromyalgia is another condition that causes muscle pain and fatigue. However, fibromyalgia is not caused by abnormalities in the immune system and the structure of the muscles is normal. Blood tests such as creatine phosphokinase and ESR are usually normal in fibromyalgia and people with this condition do not need to be treated with steroids. Fibromyalgia and myositis are not linked, i.e. people with fibromyalgia are no more likely to develop myositis than anyone else. (See arc booklet 'Fibromyalgia'.)
Should I exercise to keep up my muscle strength?
When your myositis is very active, it is probably wise to rest. However, as soon as the condition has begun to settle it is very important to do aerobic exercise so as to improve your stamina and to maintain muscle power. To start with this should be under the supervision of a physiotherapist. An occupational therapist could also advise you on how to pace yourself with your daily activities, as you may find these much more tiring than usual and it is important not to be disheartened by this.
Are there any support groups I can contact for further information?
Yes, there is the Myositis Support Group, whose contact details are given below.
Useful addresses
The Arthritis Research Campaign (arc)
PO Box 177
Chesterfield
Derbyshire S41 7TQ
Phone: 0870 850 5000
www.arc.org.uk
As well as funding research, we produce a range of free information booklets and leaflets. Please contact the address above for a list of titles or, on this website, see Publications for people with arthritis.
Arthritis Care
18 Stephenson Way
London NW1 2HD
Phone: 020 7380 6500
Helpline (freephone): 0808 800 4050
www.arthritiscare.org.uk
Offers self-help support, a helpline service, and a range of leaflets on arthritis.
Myositis Support Group
146 Newtown Road
Woolston
Southampton
Hampshire SO19 9HR
Phone: 02380 449708
www.myositis.org.uk
Information on drugs
Separate arc leaflets are available on many of the drugs used for arthritis and related conditions. We would recommend that you read the relevant leaflets for more detailed information about your medication.
