What is Myositis?

There are two types of myositis. One is called dermatomyositis (DM) and the other is polymyositis (PM).

Dermatomyositis is a condition that causes muscle weakness and skin rashes in adults and children. There’s no cure for DM, but treatment can clear the skin rash and help patients regain muscle strength for periods of time called remission.

Polymyositis also causes muscle weakness, and is more common in adults than in children.

DM symptoms include:

  • Muscle weakness – The weakness affects both sides of the body and usually happens slowly over time. It involves muscles closest to the middle of the body, such as those in the neck, shoulders, hips and thighs. Depending on the muscles involved, patients may have trouble climbing stairs, lifting things overhead, or swallowing.
  • Skin rashes – The rashes are red, sometimes scaly and patchy, and usually very itchy. Sunlight usually makes the rashes worse. DM causes different kinds of skin rashes on different parts of the body, such as:
    • Fingers, including on the backs of the finger joints and around the fingernails
    • Elbows and knees
    • Upper eyelids
    • Neck, upper chest or upper back
    • Scalp

Some people with DM have only mild symptoms. But many people have more bothersome symptoms that last years.

PM symptoms include:

  • Muscle weakness – The weakness affects both sides of the body and usually happens slowly over time. It involves muscles closest to the middle of the body, such as those in the neck, shoulders, hips and thighs. Depending on the muscles involved, patients may have trouble climbing stairs, lifting things overhead, or swallowing.

To diagnose or rule out DM and PM, your doctor or nurse will order one or more of the following tests:

  • Blood tests
  • Electromyography (EMG) – This test shows whether your muscles respond to the nerves’ electrical signals in the correct way.
  • Muscle biopsy – The doctor takes a small sample of tissue from a muscle that is weak. Then another doctor looks at the sample under a microscope.
  • Skin biopsy (for DM) – The doctor takes a small sample of skin from your skin rash. Then another doctor looks at the sample under a microscope.
  • MRI scan – This scanner creates pictures of the inside of the body, giving your doctor a more clear vision of how your muscles are affected.

DM can cause other types of long-term medical problems too, such as lung and heart problems, so it’s important to see a doctor and get diagnosed as soon as possible.