What is dermatomyositis?
Dermatomyositis is a rare acquired muscle disease that is accompanied by a rash. It is one of a group of muscle diseases called inflammatory myopathies.
Classification of inflammatory myopathies
- Dermatomyositis (DM): inflammation of voluntary muscles (myositis) in association with a rash
- Polymyositis (PM): myositis without 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 50–70 years.
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. The rash often, but not always, develops before the muscle weakness.
- Reddish or bluish-purple patches mostly affect sun exposed areas.
- A violaceous rash may also affect cheeks, nose, shoulders, upper chest and elbows.
- Purple eyelids, which are described as heliotrope, as they resemble the heliotrope flower, Heliotropium peruvianum, which has small purple petals.
- Purple papules or plaques are found on bony prominences, especially the knuckles (Gottron papules).
- Ragged cuticles and prominent blood vessels on nail folds are best seen by capillaroscopy or dermoscopy.
- A scaly scalp and thinned out hair may occur.
- Less commonly, there is poikiloderma, in which the skin is atrophic (pale, thin skin), red (dilated blood vessels) and brown (post-inflammatory pigmentation).
Calcinosis affects some people, especially children and adolescents
- It presents as hard yellow or white lumps under the skin.
- These usually appear on fingers or over joints.
- Sometimes these nodules may poke through the skin and ulcerate.
- The ulcers 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).
Muscle weakness may arise at the same time as the rash, or it may occur weeks, months or years later. Proximal muscles are affected, that is, those closest to the trunk (upper arms, thighs). 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, and are diagnostic of antisynthetase syndrome.
- Skin biopsy of the rash: the microscopic appearance of an interface dermatitis is similar to systemic (acute) 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 dermatomyositis completely resolves in about one-in-five patients. 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.