Polymyositis is a disease caused by inflammation of the muscles. This occurs when white blood cells, the immune cells of inflammation, begin to invade the muscle tissue. The muscles most severely affected are typically those closest to the trunk or torso. This results in weakness that can be severe.

Some patients with polymyositis also have lung involvement, which can cause difficulty breathing.

Risk Group

The incidence of polymyositis increases with age, with the highest rates being seen in the 35-44 and 55-64 year old age groups. Women are two times more likely to suffer from polymyositis 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

Diagnostic Tests

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


If you have polymyositis, your doctor will most likely prescribe medications that suppress the immune system, such as corticosteroids. Frequently, more than one medication will be prescribed to treat your disease. If you have lung problems, you will also see a pulmonologist at the Johns Hopkins Myositis Center.