Polymyositis and dermatomyositis: symptoms, treatment

Myositis involves muscles that are inflamed. This affects the muscle cells and leads to pain and less strength in the muscles. The cells that are affected are not replaced, so the muscles become increasingly weaker. The two most common forms of myositis are polymyositis and dermatomyositis. Polymyositis and dermatomyositis are autoimmune diseases in which the immune system turns against its own tissue. What are the symptoms and how can the diseases be treated?

Article content

  • Polymyositis
  • Dermatomyositis
  • Causes
  • Symptoms
  • Diagnosis
  • Therapy
  • Prognosis


Polymyositis is a muscle disorder that causes loss of strength and pain in various muscles. It is mainly the muscles in the upper arms and thighs that are inflamed. Polymyositis is uncommon, affecting approximately ten in every hundred thousand people. You can get it at any age. Polymyositis is not hereditary


If polymyositis is accompanied by spots on the skin, it is called dermatomyositis. In addition to the muscles, the skin is also inflamed. This can cause itching and pain, especially around the eyes and on the knuckles of the hands. In the Netherlands, five out of every million people are affected each year. It can occur at any age, but especially in children between the ages of five and fifteen and in people between the ages of forty-five and sixty. Dermatomyositis is not hereditary.


The cause of myositis is unknown, but it is suspected that the immune system does not work properly and that this is the reason why inflammation occurs. In polymyositis and dermatomyositis, the immune system targets blood vessels or muscle cells in the muscles (in addition to the usual task of detecting and removing substances and cells that do not belong in the body). Because the immune system targets its own tissues, it is called an autoimmune disease .

The condition can be activated by certain (environmental) factors, such as an infection caused by a virus. In adults, especially men, polymyositis and dermatomyositis may be related to cancer. They can also occur in combination with other autoimmune diseases, for example with systemic lupus erythematosus.


The symptoms can develop rapidly, especially in children. In adults it often takes a few weeks.

  • Muscle strain;
  • Muscles become weakened (lifting arms or standing up may be difficult);
  • Joints may be painful and swollen;
  • A tired feeling;
  • Increased body temperature;
  • If the muscles of the mouth are affected, a person will have difficulty swallowing;
  • If the heart or chest muscles are affected, shortness of breath may occur;
  • General malaise;
  • Damage to other organs such as heart, lungs, stomach and intestines may occur, especially in children;
  • There may be calcium deposits in the skin, which feels like a lump or disc and causes pain.

In dermatomyositis, the above symptoms may be preceded or followed by the symptoms below (especially around the eyes and on the hands). They can also occur in addition to the above symptoms.

  • Sore and itchy skin;
  • wounds;
  • Red rash, usually on the face, back or chest or knuckles;
  • The eyelids may be swollen and have a red-purple color;
  • Red dots near the cuticle.


If a doctor thinks that there is polymyositis and dermatomyositis, blood tests will be performed to see whether there is inflammation and whether the antibodies that match the syndromes are present. An electromyogram and a muscle biopsy can also be taken. For the latter, a sample of the tissue is taken and further examined. An electrocardiogram can be performed to check the heart muscle.


Polymyositis and dermatomyositis cannot be cured, but they can be treated reasonably well with anti-inflammatory medications. The treatment of choice is prednisone. Prednisone must be used for a long time, first in high doses and later in low doses. If the treatment does not have the desired effect, other immune suppressants can be used. Muscle stiffness can be relieved by physiotherapy. This can also improve muscle strength. Ointment can be prescribed to relieve the itching and pain of dermatomyositis. If you have problems with swallowing and feeding, a dietitian can be contacted. Sometimes surgery can be performed for painful subcutaneous calcifications.


The prognosis is more favorable in children than in adults. About seventy percent of children recover within a few years. Adults may need to take corticosteroids for years.