The exact cause of dermatomyositis is unknown, but it may be that the body's immune system mistakenly attacks healthy muscle and blood cells.
According to The Johns Hopkins Myositis Center, women are twice as likely as men to experience dermatomyositis.
Although there is no cure for the condition, some treatments are available that can help to minimize symptoms.
Doctors do not know what causes dermatomyositis but there are many theories about why it develops.
According to the American College of Rheumatology, the most commonly accepted theory is that the body's immune system attacks muscle cells and blood vessels by mistake.
Another theory suggests that dermatomyositis is caused by a virus that affects the skeletal muscles. Doctors also believe that some people are more susceptible to developing the condition due to their family history.
Symptoms of dermatomyositis appear gradually. The first symptom that a person may notice is a rash, which tends to be red and patchy in nature.
However, some people report a rash that is bluish-purple in color. The most common locations for the rash are in the following areas:
- across the shoulders and upper back
- over the knuckles, often with changes to the cuticles and nail beds
- on the palms and fingers
- over the elbows and knees
- around the eyes
- on the upper chest in a V shape
Sometimes a person will start to develop calcium deposits under the skin that may feel like hardened bumps to the touch. This is known as calcinosis and is common in children but not in adults with dermatomyositis.
Those with dermatomyositis often have "Gottron papules." These are scaly, red areas that often appear over the knuckles.
The skin symptoms associated with dermatomyositis usually give way to muscle weakness, which is likely to progress over the course of weeks or months.
Additional symptoms associated with dermatomyositis include:
- difficulty rising from a sitting to standing position
- unexplained core weakness
- pain or weakness in the joints, or both
- problems swallowing
- unexplained weakness
- feeling tired all the time, even after resting
According to the American Osteopathic College of Dermatology, an estimated 15 to 30 percent of people with dermatomyositis also experience:
- lung involvement
- problems breathing
There are some different types of dermatomyositis as well as some related conditions.
One example is juvenile dermatomyositis or JDM. This condition causes a child, usually between the ages of 5 and 10, to experience muscle weakness.
Children with JDM may have difficulty doing basic tasks, such as brushing their hair or climbing the stairs.
Children with JDM experience the following symptoms:
- problems climbing stairs
- problems brushing their hair
- problems getting up from a chair or up off the floor
- extreme tiredness
- shortness of breath
Children with JDM will also have a rash that is purple or dusky red. Sometimes doctors may mistake it for eczema.
Those with JDM are also more likely to experience inflammatory conditions, such as:
Children also experience a more sudden onset of their symptoms than adults with the condition.
Sometimes a person may develop dermatomyositis due to underlying cancer, which is known as malignancy-associated dermatomyositis.
Researchers are still studying the relationship between cancer and dermatomyositis. However, they do know that people with certain cancers are more likely to have the condition. These include cancers of the:
- GI tract
- white blood cells
A doctor will start by asking a person about their symptoms. The doctor should review all medical history and a list of medications the person takes.
Additional testing would likely include:
- Blood work: This is to rule out other conditions that could cause similar symptoms. Doctors may also test for enzymes associated with muscle breakdown that could indicate dermatomyositis. Examples include creatine kinase and aldolase. They may also look at specific antibodies that can be in dermatomyositis.
- Examining the nail beds: A lighted magnifying device is used to identify inflammation and swelling in the blood vessels of the nail beds, which is a possible sign of dermatomyositis.
- Electromyography (EMG) and nerve conduction tests: These procedures measure how well the muscles are responding to nervous system stimulation.
- Magnetic resonance imaging (MRI): This tests for any deformities in the muscles.
- Muscle biopsy: This means removing a small tissue sample of the muscle to confirm the condition is dermatomyositis.
Conditions that may initially resemble dermatomyositis include:
- systemic lupus erythematosus (SLE)
A doctor will usually try to rule out these conditions when determining whether a person has dermatomyositis.
Doctors may prescribe medications which reduce inflammation and discomfort.
Unfortunately, there is not currently a cure for dermatomyositis. Instead, doctors focus on methods to reduce inflammation and prevent further disability.
Doctors may prescribe medications to reduce inflammation, such as corticosteroids. These decrease inflammation in the body by reducing the number of antibodies the immune system produces against a particular substance.
Doctors commonly prescribe the corticosteroid prednisone to treat the initial inflammatory symptoms associated with dermatomyositis. A doctor may initially prescribe a high dose of these steroids, and then slowly decrease the dose over a number of years.
If a person cannot take corticosteroids or wishes to avoid the long-term risks associated with their use, there are alternatives. These include:
- Methotrexate: Methotrexate is often prescribed alongside corticosteroids to treat a person when they are first diagnosed with dermatomyositis. The medication is a disease-modifying agent that can reduce the body's immune response.
- Immunoglobulin: These are intravenous (IV) drugs that can block the antibodies that the immune system uses to attack the skin and muscles when a person has dermatomyositis.
- Steroid-sparing agents: Examples of these medications include cyclosporines, azathioprine, tacrolimus, anti-TNF medications, and rituximab. These medications can cause severe side effects and are usually reserved for more advanced cases of dermatomyositis.
A doctor may also recommend supportive services to help a person live better with dermatomyositis. Examples of these services include:
- Nutrition: Some individuals who have dermatomyositis can benefit from seeing a registered dietitian. A dietitian can help identify a menu that is healthful, yet features easy-to-eat foods.
- Physical therapy: Once the initial inflammation has been treated, physical therapy exercises can help to strengthen muscles, hopefully preventing them breaking down any further. A physical therapist will plan the activities according to the person's symptoms. For example, those who suffer from calcium deposits and muscle stiffness may benefit from stretching therapies. Those whose inflammation is under control may benefit from strength-building exercises.
- Speech therapy: Some people with dermatomyositis may experience difficulty swallowing as a result of muscle weakness. Speech therapy can help a person build these muscles and reduce the risk for choking and aspiration.
A person with dermatomyositis should also protect their skin from the sun's damaging rays, which seem to worsen the condition's symptoms.
Wearing a broad-spectrum sunscreen, protective clothing, and a wide-brimmed hat helps. Taking these precautions when going outdoors can reduce the incidence of skin rash and muscle weakness associated with the disease.
In rare instances, a person may require surgery to reduce the incidence of calcium deposits under the skin caused by dermatomyositis. People often undergo surgery when the deposits are causing extreme nerve pain.
The complications and outlook for dermatomyositis often depend upon:
- when a person was diagnosed with the condition
- what their associated symptoms are
For example, those diagnosed with JDM usually find that their symptoms disappear almost entirely as they get older.
However, those diagnosed with dermatomyositis as adults are less likely to experience total remission of their symptoms.
Severe and prolonged muscle weakness can lead to complications such as:
People who have dermatomyositis that affects their heart and, or lungs, may have a less positive outlook.
If someone experiences symptoms that could indicate dermatomyositis, they should speak to a doctor straight away.
The sooner that a person is diagnosed and treated, the better their outlook will be.