Polymyositis and dermatomyositis are the conditions that cause inflammation in the muscles (myositis). Polymyositis affects many areas, mainly the large muscles like those around the shoulders, hips and thighs. When polymyositis occurs alongside a skin rash it is called as dermatomyositis. They both cause pain and weakness in many muscles.
Although the symptoms may vary between individuals, most people will only have mild and short-lived symptoms. These include:
If you have dermatomyositis (myositis with a rash), you may get some of the above symptoms as well as the ones below:
Myositis has similar symptoms to fibromyalgia, another condition that causes muscle pain and fatigue. These conditions aren't related and, unlike myositis, fibromyalgia isn't an autoimmune disease. Other conditions can mimic polymyositis. These include:
In a few cases of polymyositis and dermatomyositis, drug treatment doesn't work fully and the muscles can remain weak. Although the reason is not known yet, moderate exercise still helps the recovery of your muscle strength.
Occasionally polymyositis can also affect breathing and swallowing. This may occur at the start of severe cases when the muscles used become very weak. It may also cause weakening of the heart, and inflammation of the lungs may cause scarring. This affects how the lungs work. Lung and heart conditions can cause long-term breathlessness.
Children with dermatomyositis may develop painful calcium deposits in damaged muscles. These deposits, combined with immobility, can occasionally result in permanently bent joints (flexion contracture).
Polymyositis and dermatomyositis are autoimmune diseases – conditions in which our own body’s defense system (immune system) becomes overactive and produces antibodies that fight against one’s own body tissues. This causes inflammation of the muscles and skin. The exact reason for why this happens is not yet known.
Polymyositis occasionally occurs in patients who also have another autoimmune rheumatic disease such as rheumatoid arthritis, lupus and scleroderma. The myositis is then said to be part of an overlap syndrome.
In rare occasions, myositis can be associated with cancer. Most people with polymyositis and dermatomyositis don’t develop cancer, but your doctor might arrange tests such as chest x-ray or an ultrasound scan of your abdomen and pelvis to be on the safe side.
Your doctor Will talk to you about your symptoms and examine you, but because the symptoms of polymyositis and dermatomyositis are similar to many other conditions you'll probably have blood tests and other examinations.
Creatinine phosphokinase: it is an enzyme that leaks out of damaged muscle cells. You will need repeat measurement of this enzyme throughout the course of the condition to know how well you are responding to the treatment.
Erythrocyte sedimentation rate (ESR): it detects and measures inflammation by assessing how quickly blood cells settle at the bottom of a test tube. As inflammation occurs in other conditions too, a high ESR alone won't be confirmatory for polymyositis or dermatomyositis.
Autoantibodies: NO autoantibody test proves you definitely have polymyositis or dermatomyositis, but there are tests that can be helpful in making the diagnosis. One of these is the anti- nuclear antibody test (ANA). About 80—90% Of people with polymyositis and dermatomyositis test positive for ANA, but healthy people can also test positive so it's only helpful alongside all the other information about your symptoms.
These tests may not be able to diagnose polymyositis or dermatomyositis, but they can help to rule out other conditions. You may need other tests to confirm a diagnosis.
Electromyography (EMG): A thin electrode is inserted into the muscle to record electrical discharges from nerve endings that cause your muscles to move. An unusual pattern of electrical activity in a number of different muscles suggests you have polymyositis or dermatomyositis. This test isn't painful but may be uncomfortable.
Muscle biopsy: A small sample is taken from one of your larger muscles (for example at the front of your thigh) and examined under a microscope. The site of the biopsy might be chosen using an MRI scan to assess the area. The part of the muscle that looks most badly affected on the scan Will be the site of the biopsy. You'll be given a local anesthetics to numb the area while the sample is taken, but there may be some discomfort for a few days afterwards. The biopsy may show White blood cells sticking to the covering of the muscle and damaging the proteins that make your muscles contract, which causes the weakness and fatigue. You may need to have a repeat biopsy if your condition doesn't improve with standard treatments. This is to check for the proteins found in inclusion body myositis (IBM). You may see different specialists depending on which symptoms are giving you the most trouble. You could be referred to one or more of the following people:
Treatment for polymyositis and dermatomyositis includes a combination of drug treatment and exercise.
Steroids (tablets or injections): these are the first choice of treatment. Usually they are given at higher doses to begin with. As the steroids can have side-effects, your doctor will reduce the dose as quickly as possible.
Other drugs may be prescribed alongside the steroids to risk with or to reduce the flare-up of your condition when the steroid dose is lowered. The most common drugs used are:
These are all types ofdisease-modifying anti-rheumatic diseases (DMARDs), and you will need regular blood tests to check for any possible side-effects.
Occasionally these drugs may not be able to control the disease. In a small number of people with sever muscle disease and complications have therefore been treated with therapies biologic. Biologics are the newer type of DMARDs. They work by blocking the process of inflammation. Examples include infliximab and rituximab.
Infusion of intravenous immunoglobulins might also be given, though most people won't need these. Immunoglobulins are antibodies that stop your immune system attacking your body's own tissues. Infusions are given in hospital at monthly or 3-monthly intervals. Sometimes you might a feel a little unwell (as if you have flu) during the infusion.
Even in severe cases myositis usually responds well to treatment, although many people need life-long drug treatment to keep their condition under control.
It's probably best to rest when your myositis is very active, but once it's calmed down you'll need to start exercises. Aerobic exercise (any exercise that makes you breath more heavily and your heart beat faster) is especially important to help restore muscle strength and improve stamina. At first this should be done under the supervision of a physiotherapist, who'll give you a tailored program to suit your specific needs. Very strenuous exercise should be avoided.
Children with juvenile dermatomyositis will need more vigorous physiotherapy to prevent flexion contracture — this is a condition where the joints, especially the knees, become permanently bent. Some people with severe inflammation never fully recover but most people do, though it may take several months for muscle strength to improve. It may take weeks or months for your body to repair your muscles and you may get tired more quickly than normal, so don't worry if you're not back to full strength straight away.
The outlook for people with polymyositis and dermatomyositis is good. Symptoms aren't often severe and in most cases the pain and feelings of being unwell can be eased fairly quickly with drug treatment. Even in severe cases myositis responds to treatment. The condition frequently becomes inactive. Muscle strength will take longer to recover, but once the disease is controlled with treatment you'll be given exercises to counter any muscle wasting and to improve the strength of the recovering muscle.