What is dermatomyositis?
Dermatomyositis is a rare acquired muscle disease that is accompanied by a skin rash. It is just one of a group of muscle diseases called inflammatory myopathies.
Types of inflammatory myopathies
|Dermatomyositis (DM)||Inflammation of voluntary muscles (myositis) in association with a skin rash|
|Polymyositis (PM)||Myositis without skin rash|
|Juvenile DM/PM||Myositis and skin rash occurring in children <18 years|
|Amyopathic DM||Typical skin rash develops without evidence of muscle involvement. Also called dermatomyositis sine myositis.|
|Antisynthetase syndrome||Myositis, arthritis, interstitial lung disease, mechanic's hands and Raynaud phenomenon|
Who gets dermatomyositis?
Dermatomyositis may affect people of any race, age or sex, although it is twice as common in women than in men. The onset of the disease is most common in those aged 50 to 70.
What are the signs and symptoms of dermatomyositis?
In many patients the first sign of dermatomyositis is the presence of a symptomless, itchy or burning rash.
- Reddish or bluish-purple patches, mostly on sun exposed areas
- Purple eyelids, which are described as
heliotrope, as they resemble the heliotrope flower, e.g., Heliotropium peruvianum, which has small purple petals.
- Purple spots on bony prominences, especially the knuckles, which are known as
- Ragged cuticles and prominent blood vessels on nail folds
- The rash may also affect cheeks, nose, shoulders, upper chest and elbows
- A scaly scalp and thinned out hair may occur
- Less commonly there is poikiloderma i.e. the skin is atrophic (pale, thin skin), red (dilated blood vessels) and brown (post-inflammatory pigmentation)
Prominent nail fold capillaries
Some people, especially children and adolescents, develop hard yellow or white lumps under the skin, called calcinosis. These usually appear on fingers or over joints. Sometimes these nodules may poke through the skin and they may become infected. Some patients have swollen joints and Raynaud phenomenon (this term refers to fingers that go very white and stiff in cold conditions, then purple as they warm again).
The skin rash often, but not always, develops before the muscle weakness. Muscle weakness may arise at the same time as the rash, or it may occur weeks, months or years later. Proximal muscles are affected, i.e. those closest to the trunk. The first indication of myositis is when the following everyday movements become difficult.
- Climbing stairs or walking
- Rising from a sitting or crouching position
- Lifting objects
- Raising arms above the shoulders, e.g. combing hair
- Difficulty swallowing (dysphagia)
Occasionally the affected muscles ache and become tender to touch.
What tests are performed?
The diagnosis of dermatomyositis is usually confirmed by the following tests.
- Blood test to detect raised circulating muscle enzymes: creatine kinase (CK) and sometimes aldolase, aspartate aminotransferase (AST) and lactic dehydrogenase (LDH)
- Blood test to detect autoantibodies: non-specific antinuclear antibody (ANA) is found in most patients, specific Anti-Mi-2 is found in one quarter and Anti-Jo-1 in a few, usually those who have lung disease.
- Skin biopsy of the rash: the microscopic appearance is similar to lupus erythematosus
- Biopsy of an affected muscle
- Electromyography (EMG) testing
- Magnetic resonance imaging (MRI) scan of muscles
In those over 60, full body examination and testing are recommended, looking for underlying cancer.
What causes dermatomyositis?
Dermatomyositis is considered one of the connective tissue diseases, like systemic sclerosis and lupus erythematosus. Why dermatomyositis occurs remains unknown but research is taking place to identify factors that may play a part in its development, some of which are listed below.
- Genetic predisposition
- Underlying cancer (more likely in the elderly)
- Autoimmune defect (immune reaction against self)
- Infectious or toxic agents acting as triggers
- Drug-induced (implicated drugs include hydroxyurea, penicillamine, statins, quinidine, and phenylbutazone)
Treatment of dermatomyositis
The primary aim of treatment is to control the skin disease and the muscle disease. An oral corticosteroid such as prednisone in moderate to high dose is the mainstay of medical therapy and is given to slow down the rate of disease progression. Immunosuppressive or cytotoxic drugs may also be used including methotrexate, azathioprine, cyclophosphamide, ciclosporin, mycophenolate, high dose intravenous immunoglobulin and experimentally, biologics such as rituximab. Other important measures in the management of dermatomyositis include:
- Diltiazem, a calcium channel blocker usually prescribed for high blood pressure, may reduce calcinosis
- Colchicine has also been reported to reduce calcinosis
- Hydroxychloroquine may reduce the photosensitive rash
- Avoid excessive sun exposure and use sun protection measures, including sunscreens, to minimize the harmful effects of the sun on already damaged and photosensitive skin
- Bedrest for those with severe inflammation of muscles
- Physical therapy and activity to keep the muscles and joints moving
- Avoid eating food before bedtime and raising the bed head for those with difficulty swallowing
Most patients will require treatment throughout their lifetime, but it completely resolves in about 20%. Patients who have disease affecting their heart or lungs, or who also have an underlying cancer do less well and may ultimately die from their disease.
See the DermNet NZ bookstore
On DermNet NZ:
- The Myositis Association
- Dermatologic Manifestations of Dermatomyositis – Medscape Reference
- Dermatomyositis – British Association of Dermatologists
Books about skin diseases:
See the DermNet NZ bookstore