Author: Vanessa Ngan, Staff Writer, 2003.

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.

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.

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.

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.

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:

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.

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