Symptoms and causes

Symptoms

The muscle weakness associated with polymyositis involves the muscles closest to the trunk, such as those in your hips, thighs, shoulders, upper arms and neck. The weakness affects both the left and right sides of your body, and tends to gradually worsen.

When to see a doctor

Seek medical attention if you develop unexplained muscle weakness.

Causes

The exact cause of polymyositis is unknown, but the disease shares many characteristics with autoimmune disorders, in which your immune system mistakenly attacks your own body tissues.

Complications

Possible complications of polymyositis include:

  • Difficulty swallowing. If the muscles in your esophagus are affected, you may have problems swallowing (dysphagia), which in turn may cause weight loss and malnutrition.
  • Aspiration pneumonia. Difficulty swallowing may also cause you to breathe food or liquids, including saliva, into your lungs (aspiration), which can lead to pneumonia.
  • Breathing problems. If your chest muscles are affected by the disease, you may experience breathing problems, such as shortness of breath or, in severe cases, respiratory failure.

Associated conditions

Although these are not complications, polymyositis is often associated with other conditions that may cause further complications of their own, or in combination with polymyositis symptoms. Associated conditions include:

  • Raynaud's phenomenon. This is a condition in which your fingers, toes, cheeks, nose and ears initially turn pale when exposed to cold temperatures.
  • Other connective tissue diseases. Other conditions, such as lupus, rheumatoid arthritis, scleroderma and Sjogren's syndrome, can occur in combination with polymyositis.
  • Cardiovascular disease. Polymyositis may cause the muscular walls of your heart to become inflamed (myocarditis). In a small number of people who have polymyositis, congestive heart failure and heart arrhythmias may develop.
  • Lung disease. A condition called interstitial lung disease may occur with polymyositis. Interstitial lung disease refers to a group of disorders that cause scarring (fibrosis) of lung tissue, making lungs stiff and inelastic. Signs and symptoms include a dry cough and shortness of breath.
  • Cancer. People who have polymyositis have an elevated risk of cancer.
July 21, 2017
References
  1. Polymyositis and dermatomyositis. Merck Manual Professional Version. http://www.merckmanuals.com/professional/musculoskeletal-and-connective-tissue-disorders/autoimmune-rheumatic-disorders/polymyositis-and-dermatomyositis. Accessed April 13, 2017.
  2. Facts about inflammatory myopathies (myositis). Muscular Dystrophy Association. https://www.mda.org/sites/default/files/publications/Facts_Inflamm_Myopathies_P-199.pdf. Accessed April 13, 2017.
  3. Polymyositis information page. National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/Disorders/All-Disorders/Polymyositis-Information-Page. Accessed April 13, 2017.
  4. Goldman L, et al., eds. Inflammatory myopathies. In: Goldman-Cecil Medicine. 25th ed. Philadelphia, Pa.: Saunders Elsevier; 2016. https://www.clinicalkey.com. Accessed April 13, 2017.
  5. Daroff RB, et al. Disorders of skeletal muscle. In: Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, Pa.: Saunders Elsevier; 2016. https://www.clinicalkey.com. Accessed April 13, 2017.
  6. Miller ML, et al. Treatment of recurrent and resistant dermatomyositis and polymyositis in adults. http://www.uptodate.com/home. Accessed April 13, 2017.
  7. Miller ML, et al. Initial treatment of dermatomyositis and polymyositis in adults. http://www.uptodate.com/home. Accessed April 13, 2017.
  8. Chang-Miller A (expert opinion). Mayo Clinic, Rochester, Minn. April 23, 2017.