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Polymyositis: Autoimmune condition with muscle weakness

Polymyositis is a rare chronic inflammatory disease in which skeletal muscle is damaged. These are the muscles necessary for making movements. This autoimmune condition leads to muscle weakness on both sides of the body and tissue damage also occurs. Other symptoms occur with this progressive disease. The disease is treated through medication and physiotherapy, which improves muscle strength and function. The prognosis of the inflammatory condition is variable. If left untreated, polymyositis leads to potentially life-threatening complications.

  • Epidemiology polymyositis
  • Causes of chronic autoimmune disease
  • Polymyositis and other conditions
  • Symptoms: Progressive muscle weakness in the trunk
  • Diagnosis and examinations
  • Treatment via medication and therapy
  • Prognosis is variable
  • Complications of chronic muscle disease


Epidemiology polymyositis

Polymyositis most often affects patients in the third to fifth decades. Patients with a black skin color are affected more often than people with a white skin color. The disease has a predilection for women. The disease also occurs all over the world.

Causes of chronic autoimmune disease

The precise cause of polymyositis is not known, but the disease shares many characteristics with autoimmune diseases, causing the immune system to mistakenly attack the body’s own tissues. The white blood cells spontaneously attack the muscles.

Polymyositis and other conditions

Sometimes the disease is accompanied by a characteristic skin rash; then there is dermatomyositis. Other conditions that may be associated with polymyositis include cancer, systemic lupus erythematosus, scleroderma (build-up of scar tissue in the skin and organs), rheumatoid arthritis (chronic autoimmune disorder with inflammation of joints and other organs) and Sjögren’s syndrome (disease of eyes, mouth and throat).

Symptoms: Progressive muscle weakness in the trunk

The symptoms of polymyositis usually develop gradually over several weeks or even months. The patient presents with widespread, painful, inflammatory muscle changes and muscle weakness. The muscles near the torso (hips, thighs, shoulders, upper arms and neck) are particularly affected on both sides. These symptoms may cause the patient to have difficulty climbing stairs, getting up from a sitting position, or lifting objects above the head. This also results in swallowing problems (medical term: dysphagia), speech problems (due to weak throat muscles) and shortness of breath. In addition, the patient has swelling of the abdomen, erythema (red rash in several places), morning stiffness, loss of appetite, weight loss, constipation, shortness of breath (dyspnea), fever, fatigue, joint pain and later often contractures (permanent contraction of tissues due to wasting) and/or calcinosis (deposits of calcium salts in organs or tissues in various places in the body, with or without alkalosis (too low acidity of the blood) or with an increased calcium level in the blood). The disease is slowly progressive, causing the symptoms of polymyositis to slowly worsen.

Diagnosis and examinations

Diagnostic research

Blood test The doctor carries out a blood test. Elevated muscle enzymes often indicate the presence of muscle damage. In addition, this shows specific autoantibodies associated with various symptoms of polymyositis , which is useful for developing a treatment plan.Results of an EMG: electromyogram / Source: D. Gordon E. Robertson, Wikimedia Commons (CC BY-SA-3.0)Electromyography An electromyography is also important (measurement of electrical muscle activity). This research is necessary to determine the spread of the disease.MRI scan Magnetic resonance imaging is a diagnostic test in which the scanner creates cross-sectional images of the affected muscles.Muscle biopsy The doctor performs an operation in which he removes a small piece of muscle tissue for laboratory research. A muscle biopsy provides information about abnormalities in muscles, such as inflammation, damage or infection. Further research is carried out in the laboratory into the presence of abnormal proteins and enzyme deficiencies. A muscle biopsy in patients with polymyositis usually shows inflammation, dead muscle cells (necrosis), and degeneration and regeneration of muscle fibers.Urinalysis The doctor measures the myoglobin content in the urine during the urine examination.

Differential diagnosis

The following diseases mimic the symptoms of polymyositis and are therefore the differential diagnosis of the inflammatory disease:

  • amyotrophic lateral sclerosis (neurodegenerative disorder with paralysis of limbs first and then other muscles and nerves)
  • fibromyalgia (chronic condition with pain and fatigue)
  • hyperthyroidism (overactive thyroid gland)
  • hypothyroidism (underactive thyroid gland)
  • iatrogenic Cushing’s syndrome (too much cortisol in the body with symptoms in the skin, muscles and bones)
  • rheumatoid arthritis
  • sarcoidosis (disease of the skin, eyes, lungs and nervous system)
  • muscular rheumatism (inflammatory muscle disease)
  • systemic lupus erythematosus (SLE)
  • trichinosis (worm infection with symptoms in the stomach, intestines and muscles)


Treatment via medication and therapy

Polymyositis cannot be cured, but the function and strength of the muscles can be improved. Early diagnosis and treatment increases the chance of effective results and reduces the risk of complications.


The most commonly used drugs to treat polymyositis include:

  • Corticosteroids are powerful anti-inflammatory drugs useful in polymyositis. However, long-term use is not recommended because it leads to serious and major side effects. The doctor therefore gradually reduces the dose.
  • Corticosteroid sparing agents: The patient takes this medication in combination with corticosteroids, which reduces the side effects and the patient requires a lower dose of corticosteroids.
  • Rituximab (Rituxan) is a medication that the patient takes when the other medications are not working.



The patient receives intravenous immunoglobulin, a purified blood product that contains healthy antibodies from thousands of blood donors. These healthy antibodies block the harmful antibodies that attack the muscles in polymyositis. This is done via an intravenous infusion. This treatment gives varying results.


Other possible therapies include physiotherapy (to improve strength and flexibility), speech therapy (to help with swallowing problems) and nutritional advice (for chewing and swallowing problems).

Prognosis is variable

The prognosis for polymyositis varies. All patients respond differently to the treatment of polymyositis. Many patients, especially children, recover from the disease without additional treatment. However, most adults require immunosuppressants to combat the disease. However, most patients respond well to treatment. Occasionally this is not the case and severe, progressive muscle weakness occurs, causing the patient to develop pneumonia or breathing problems. Occasionally a patient dies from polymyositis.The main causes of death are:

  • respiratory failure (severe illness with slow breathing)
  • pneumonia or other lung diseases
  • severe, long-term muscle weakness
  • cancer
  • malnutrition


Complications of chronic muscle disease

Complications of polymyositis include:

  • abdominal complications
  • aspiration pneumonia (pneumonia due to inhaling foreign substances)
  • congestive heart failure (poor pumping of blood through the heart)
  • dysphagia (difficulty swallowing)
  • a heart block
  • an infection
  • a pneumonia
  • a myocardial infarction (death of a piece of the heart muscle: (heart attack))
  • heart and vascular disease
  • cardiac arrhythmias
  • interstitial lung diseases (scarring and inflammation in the lungs)
  • calcium deposits in the affected muscles, especially in children with the disease
  • cancer (especially breast cancer and lung cancer)
  • pulmonary fibrosis (scarring of lungs with shortness of breath)
  • lung diseases
  • malabsorption (problems with nutrient absorption)
  • pericarditis (inflammation of the membrane surrounding the heart)
  • retinopathy (damage to the retina)
  • steroid myopathy or other complications of corticosteroid treatment


read more

  • Autoimmune disorder: Body attacks its own immune system
  • Muscle weakness (weak muscles): Decreased muscle strength