Author: Vanessa Ngan, Staff Writer, 2003.
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.
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.
Dermatomyositis is considered one of the connective tissue diseases, like systemic sclerosis and lupus erythematosus. Dermatomyositis is thought to be caused by microangiopathy affecting skin and muscle.
Factors that may play a part in its development are listed below.
Dermatomyositis is characterised by cutaneous features and myositis.
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.
See more dermatomyositis images.
Muscle weakness may arise at the same time as the dermatomyositis 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.
Occasionally the affected muscles ache and become tender to touch.
Calcinosis affects some people, especially children and adolescents
Some patients have swollen joints (arthritis) and Raynaud phenomenon (this term refers to fingers that go very white and stiff in cold conditions, then purple as they warm again).
The following tests usually confirm the diagnosis of dermatomyositis.
In those over 60, full body examination and testing are recommended, looking for underlying cancer.
The primary aim of treatment is to control the skin disease and 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.
Hydroxychloroquine may reduce the photosensitive rash. Note that adverse cutaneous reactions to hydroxychloroquine are reported to affect more than 30% of patients with dermatomyositis, compared to a lower risk of rash in patients with cutaneous lupus erythematosus .
Immunosuppressive or cytotoxic drugs may also be used including methotrexate, mycophenolate mofetil, azathioprine, cyclophosphamide, ciclosporin, high dose intravenous immunoglobulin and experimentally, biologics such as rituximab.
Most patients will require treatment throughout their lifetime, but dermatomyositis completely resolves in about one-in-five patients. Patients who have a disease affecting their heart or lungs, or who also have underlying cancer, do less well and may ultimately die from their disease.
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