Polymyositis – Causes, Symptoms, Diagnosis, Treatment

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Polymyositis is an inflammatory disease that affects the muscles and surrounding tissues, including blood vessels. It is a rare autoimmune disease, with an annual incidence of 8 per million. It can affect children but normally manifests in adults over the age of 20, impacting females more often than males.

Causes of Polymyositis

Polymyositis has no clear cause and is not fully understood. While not a genetic disorder, the incidence may be affected by genetic factors. May also be triggered by a virus or exposure to certain kinds of drugs, such as interferon-alpha.

Symptoms of Polymyositis

Symptoms generally consist of a gradually worsening weakness and tenderness in the muscles of the torso, specifically in the neck, shoulders, upper back, upper arms, hips, and thighs. Daily activities, such as reaching high cabinets, brushing/fixing hair, taking the stairs, or even lifting one’s head off a pillow can be compromised. Getting up from a fall or even a chair becomes difficult. Sometimes weakness in the neck muscles can affect the ability to chew and swallow.

Diagnosis of Polymyositis

A diagnosis of polymyositis is made based on a review of the reported symptoms, family medical history, a physical examination, and most often lab tests and a muscle biopsy. Lab Tests include:

  • A blood test to measure the presence of creatine kinase (CK), which would normally be high in a patient with polymyositis
  • A blood test to look for the presence of antibodies common in autoimmune diseases
  • An electromyogram, which tests electrical activity in muscles
  • A nerve conduction velocity test, which assesses the speed and strength of nerve impulses 

Complications of Polymyositis

When muscles and surrounding blood vessels become inflamed and constricted, they can damage other organs of the body as well:

  • inflammatory cardiomyopathy, a condition affecting the heart muscle
  • difficulty breathing, due to muscle weakness and/or inflammation of the lungs and surrounding tissue
  • dysphagia, trouble swallowing due to muscle weakness in the neck

Treatment of Polymyositis

Polymyositis is an extremely treatable disease, normally with drugs that suppress the immune system:  

  • Corticosteroids such as prednisone – generally the first course of treatment. The side effects of prednisone, such as weight gain (including redistribution of fat from the extremities to the face and abdomen), psychological and/or vision problems, often lead both doctors and patients to seek alternative treatments in long-term situations, such as
  • Immunosuppressants such as methotrexate and cyclosporine
  • Intravenous Immunoglobulins (IVIg) – antibodies harvested from donors and injected into patients, designed to “confuse” the immune system, thereby stopping the attack.

Prognosis of Polymyositis

With proper treatment, some people experience a full recovery, some people experience greatly reduced symptoms, and some people are required to take medication for the rest of their lives. Most patients experience increased quality of life. In some cases, there is permanent muscle atrophy and loss of strength, while in other cases there is a full recovery of muscle size and strength.


  1. mda.org
  2. myositis.org
  3. https://www.rheumatology.org