Dermatomyositis is an acquired disorder due to inflammation in the muscle and skin. Children and adults may both be affected, with females being more likely to acquire it than males. It mainly affects the muscles of the hips and thighs, the upper arms, the top part of the back, the shoulder area and the neck.
It is an autoimmune disorder, meaning that a person’s white blood cells which are supposed to fight off bacteria and viruses, begin to attack their own muscles. While it is not known what triggers a person’s immune system to behave in this way, there are many theories that suggest it is a combination of one’s genetic predisposition, and environmental exposures. Persons not only of either sex, but also of any age can get dermatomyositis. Apart from females being slightly more predisposed, so too are people in middle childhood and their twenties. It is sometimes associated as well with other autoimmune diseases such as lupus, scleroderma, and rheumatoid arthritis. In rare cases it can be linked to certain types of cancer.
You experience weakness, muscle soreness, bumps of calcium deposits under the skin, and a red, scaly rash on the elbows, knees, chest, and face. Some patients with dermatomyositis will have trouble swallowing.
The weakness usually develops slowly over weeks to months, although rare cases can begin over days. This weakness most commonly affects the muscles of the arms and legs. Patients often realise that they have difficulty getting out of chairs, or climbing stairs. It does not typically involve the eyes, heart, or breathing muscles. However, the muscles involved in swallowing can become weak. Muscle pain may also be a prominent symptom because of the disorder’s association with inflammation in the muscles.
The rash associated with dermatomyositis can look very similar to a number of other rash types, and except by skin biopsy, there is nothing that distinguishes it from a host of others. In its most typical form, the rash maybe reddish, or even purplish, and extends across the face, chest, fingers and neck. Some patients may even lose their hair. Clinically, the appearance is often quite characteristic to neurologists, rheumatologists, and dermatologists.
The diagnosis begins with the patient’s history and performance of a clinical exam, especially examining the rashes. A physician who suspects a diagnosis of dermatomyositis, may perform blood tests, an EMG, or a magnetic resonance imaging scan (MRI). The blood tests confirm elevated levels of enzymes which are found in muscle. Without elevated levels of one of these enzymes, it is very unlikely to have a diagnosis of dermatomyositis. The EMG test looks at the function of a patient’s muscles and will reveal evidence for muscle inflammation and damage. An MRI looks for visual evidence of inflammation in a group of muscles. It can also be used to choose which muscle to biopsy.
If these three non-invasive tests suggest a diagnosis of dermatomyositis, then patients should have a muscle biopsy before beginning therapy. A muscle biopsy is needed in all patients for a definitive diagnosis. Finally, there are a very specific set of blood tests called Myositis Specific Autoantibodies. These antibodies are found in 20-30% of affected patients, but are important because they can predict the presence of other associated conditions.
Therapy is directed at altering a patient’s immune system. All of these therapies therefore have some significant risk of side effects, so treatment needs to be undertaken only with physicians accustomed to using these medications, and monitoring their side effects. Corticosteroids are often used as a first line therapy, because they decrease the muscle inflammation. These can be effective in a matter of weeks. If the corticosteroids are ineffective, other immunosuppressive medications may be given. Intravenous immunoglobulin has also been shown to be effective in select cases.
In most people once this disease begins, there is no clear way to cure it. There are, however, several effective treatments which exist that can improve a person’s muscle strength. In most cases people can resume their usual level of function. Further research is being done, and it is hopeful that eventually a cure would be found.