What is Dermatomyositis?
Dermatomyositis (DM) is classified both as a neuromuscular disease and an autoimmune disease. It is thought that the inflammation resulting in cell damage is created when the immune system attacks healthy muscle tissue and blood vessels under the skin.
DM is one of several diseases in the Idiopathic Inflammatory or Acquired Myopathy category. The term “idiopathic” means no known cause, however some cases are known to have been caused by medications, viruses, bacteria, trauma, toxins, cancer or other illness.
It is called an “acquired” myopathy because it is not an inherited disorder. However it is thought that people with DM may have a genetic predisposition and some factor, such as the ones mentioned above, triggers the immune system, which goes haywire and attacks healthy cells.
Characteristic of Dermatomyositis
There can be significant variation in symptoms from patient to patient. Not everyone diagnosed with Dermatomyositis will display all the symptoms, and the intensity of the symptoms can vary widely.
Muscle weakness can develop over a period of days, weeks or months, is typically symmetrical (both sides of the body) and affects proximal muscles (muscles which are closest to the body’s core), such as the quadriceps, hip flexors, neck, shoulder and deltoid muscles. This weakness often leads to difficulty climbing stairs, rising from a chair or the floor, turning in bed, lifting, styling hair or reaching over the head for something like an item on a shelf. Muscle weakness may be accompanied by pain (myalgia).
Dermatomyositis is considered a chronic disease with no known cure, however, many people respond well to certain treatments or combination of treatments with improvement in symptoms or complete remission of symptoms. As discussed in detail in the Treating Myositis section, finding the most effective treatment for your specific symptoms can be a challenge.
Some patients, although not common, experience weakness in distal muscles, those farthest away from the body’s core such as hands and fingers.
Dermatomyositis is considered a rare disease. Approximately 5 to 10 people per million are diagnosed in the US with a form of Myositis each year.
The second manifestation of DM, and the reason the term “dermato” is used, is skin involvement, which frequently develops before the muscle weakness. DM is considered to be the easiest form of Myositis to diagnose due to the characteristic “heliotrope” rashes. Heliotrope refers to the pink-purple-violet shade of the heliotrope flower.
The rashes often appear on the eyelids and the face, as well as around the knuckles, nails, knees, elbows, back and chest region, which is referred to as the “shawl” rash. The rash has a tendency to be blotchy with blue-purple stains and, in many cases, is the first symptom of Dermatomyositis. Some may be painful, itchy, and intense enough to disturb sleep.
Amyopathic Dermatomyositis (ADM)
There is a subset of DM which has skin manifestations only with no muscle involvement, this is called Amyopathic Dermatomyositis (ADM), or Dermatomyositis Sine Myositis. About half of those diagnosed with ADM suffer from fatigue. Other significant potential complication of ADM is a higher risk for cancers, particularly internal malignancies and rapidly-progressing lung disease.
When Dermatomyositis is suspected, physicians will also request lab work for certain tests such as the Myositis Specific Antibodies (MSA), Antinuclear Antibodies (ANA) and Myositis Associated Antibodies (MAA) panels. If the patient tests positive to certain antibodies, the results may offer physicians the best chance of treating the disease successfully as well as offering “predictors” of possible disease progression and complications.
Signs and Symptoms of Dermatomyositis
Complications of Dermatomyositis
Dermatomyositis in images
Dermatomyositis and Cancer
Cancer can be an underlying cause of Dermatomyositis and may precede its onset. If the cancer precipitated DM, removal of the cancer may result in remission of the Dermatomyositis.
Dermatomyositis in adults has also been linked to an increased likelihood of developing cancer post diagnosis, particularly cancers of the cervix, lungs, pancreas, colorectal system, breasts, ovaries and gastrointestinal tract and non-Hodgkin’s lymphoma. The risk of cancer appears to level off about three years after a diagnosis of DM. The incidence of cancer is higher in Dermatomyositis than in Polymyositis, and particularly in those with certain antibodies. It is strongly suggested that appropriate cancer screenings be conducted upon diagnosis and in the years after a Myositis diagnosis.
Because of a high cancer risk, both before and after diagnosis, doctors will often perform cancer screenings at the onset or suspicion of Dermatomyositis. Cancer will continue to be a risk with such patients, and cancer screening should be continued on a regular basis and more often than suggested for the patient’s age group per doctor’s advice, particularly because of the increased cancer risk of immune-suppressing treatments.
Muscle biopsy comparison of normal muscle tissue versus muscle tissues affected with Dermatomyositis.
Image courtesy of
The Muscular Dystrophy Association
“Simply Put” is a service of Myositis Support and Understanding, to provide overviews of Myositis-related medical and scientific information in understandable language.
MSU volunteers, who have no medical background, read and analyze often-complicated medical information and present it in more simplified terms so that readers have a starting point for further investigation and consultation with healthcare providers. The information provided is not meant to be medical advice of any type.