What is Dermatomyositis

Dermatomyositis is a systemic muscle disorder of unknown origin that causes muscle weakness and characteristic skin changes. Polymyositis causes a similar muscle weakness, but without the skin changes.

Statistics on Dermatomyositis

Dermatomyositis is rare. The disease is diagnosed in 2-10 people per million each year.

Risk Factors for Dermatomyositis

Dermatomyositis may occur at any age, but commonly onset is following middle-age. It is more common in Caucasians and females are affected about twice as often as males. The average age of onset in juvenile dermatomyositis is between five and 14 years. This subgroup of patients has a better prognosis than adult patients.
Cause remains unknown. A number of studies have suggested an association with viruses, drugs and immunological mechanisms.

Progression of Dermatomyositis

Studies have shown an increased risk of developing certain forms of cancer in adults patients with dermatomyositis. The most common reported cancers include ovarian and gastric cancer, and lymphoma. A thorough examination at diagnosis is important, as are regular follow-up appointments.

How is Dermatomyositis Diagnosed?

Investigations normally performed include blood tests to measure muscle enzymes and specific antibodies. Electromyography, a test that measures electrical activity within muscle fibers usually shows abnormalities. MRI may be useful.

Prognosis of Dermatomyositis

With early diagnosis and treatment, prognosis is good. Survival rates of 80 and 73% at five and eight years respectively have been reported. Factors which point to a poor outcome include late diagnosis, difficult-to-treat disease, older age, cancer, fever, difficulty swallowing and fibrosis in the lungs.

How is Dermatomyositis Treated?

Goals of treatment are to improve function and prevent disability. Treatment should be started early, with co-ordination between the physiotherapist, dermatologist and general practitioner.
The aim of physiotherapy is to prevent muscle wasting and loss of movement. Initial therapy consists of passive stretching and splinting, with strength-building exercises once inflammation subsides. Wearing sunscreen and protective clothing is advised. Antihistamines may be useful in controlling symptoms of itching.
Steroid medications, such as prednisolone are the treatment of choice. In difficult-tp-treat cases, the addition of an immunosuppressant drug may be necessary.

Dermatomyositis References

  1. Bligh, Farrow. Interactive case report: A 66 year old woman with a rash: case progression. BMJ 2003;326:640.
  2. Koler, Montemarano. Dermatomyositis. Am F Phys 2001. (online) http://www.aafp.org/afp/20011101/1565.html
  3. Kumar and Clark. Clinical Medicine 5th ed. 2002. WB Saunders
  4. Tierney, McPhee, Papadakis. Current Medical Diagnosis and Treatment, 40th ed.2001. Lange.

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