Dermatomyositis is characterized by a rash that precedes or accompanies muscle weakness. The cause is unknown.

The rash that accompanies the symptoms of muscle weakness looks like patchy, bluish-purple discolorations on the face, neck, shoulders, upper chest, elbows, knees, knuckles, or back. Some people may also develop calcium deposits, which appear as hard bumps under the skin.

The most common symptom of dermatomyositis is muscle weakness, usually affecting the muscles that are closest to the trunk of the body. Some patients also have lung involvement, which can cause difficulty breathing.

Risk Group

People all over the world can suffer from dermatomyositis. Women are at least two times more likely to suffer from dermatomyositis than men.


  • The gradual onset of weakness over weeks or months
  • Difficulty rising from a low-seated chair or combing one’s hair
  • Torso or “core” weakness
  • Difficulty swallowing (dysphagia)
  • Pain or weakness in the joints
  • Generalized fatigue
  • Patchy, reddish rash on the eyelids, cheeks, bridge of the nose, back or upper chest, and joints. In some cases, the development of hardened bumps under the skin.

Diagnostic Tests

  • Your doctor will ask for a complete medical history and will perform a thorough physical examination.
  • Blood work will be obtained.
  • Electromyography (EMG) and nerve conduction tests may be performed.
  • Magenetic resonance imaging (MRI) of affected muscle may be requested.
  • After the doctor sees you and reviews the results of your testing, a muscle biopsy may be required to confirm the diagnosis of dermatomyositis. This is a minor procedure that can be performed by a doctor at the Johns Hopkins Myositis Center.


If you have dermatomyositis, your doctor will most likely prescribe medications that suppress the immune system, such as corticosteroids. If you have severe skin involvement, you may also see a dermatologist. If you have lung problems, you will also see a pulmonologist at the Johns Hopkins Myositis Center.