Polymyositis (pol-e-my-o-SY-tis) is an uncommon inflammatory disease that causes muscle weakness affecting both sides of your body. Having this condition can make it difficult to climb stairs, rise from a seated position, lift objects or reach overhead.
Polymyositis most commonly affects adults in their 30s, 40s or 50s. It's more common in blacks than in whites, and women are affected more often than men. Signs and symptoms usually develop gradually, over weeks or months.
While there is no cure for polymyositis, treatment — ranging from medications to physical therapy — can improve your muscle strength and function.
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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.
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.
Your risk of polymyositis is higher if you have lupus, rheumatoid arthritis, scleroderma, or Sjogren's syndrome.
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.
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.