Myositis, Polymyositis, Inflammatory Myopathy

Myositis is an inflammation of muscle tissue that may cause muscle weakness. The potential conditions that can cause myositis include injuries, infection, medications or autoimmune diseases.

Along with muscle weakness, you may experience a rash, fatigue after mild exercise, and some swelling or pain.

Myositis may appear in different forms.

  • Polymyositis occurs when muscle weakness affects both sides of your body. The symptoms usually develop gradually and typically affect people in their 30s, 40s and 50s.
  • Dermatomyositis appears as muscle weakness along with a distinctive skin rash. This form of myositis can affect children (usually between the ages of 5‒15) and adults (typically between the ages of late 40s to early 60s).
  • Inclusion body myositis is caused by a combination of two factors: inflammation and degeneration.

Myositis may be caused by various factors.

  • Injuries from vigorous exercise can cause myositis, but this usually resolves itself after rest. 
  • Infections, such as the common cold, flu or HIV, can cause myositis.
  • Drugs, such as cocaine, alcohol, statins (to treat cholesterol), colchicine (to treat gout) and hydroxychloroquine (to treat malaria), may cause myositis. A relatively rare and dangerous condition, rhabdomyolysis, can be caused from taking statins; it causes massive deterioration of muscle tissue and a resulting secretion of protein in urine and can lead to kidney damage.
  • Inflammation induced by autoimmune diseases may trigger myositis symptoms; polymyositis, dermatomyositis and inclusion body myositis are among the common causes. Lupus, scleroderma and rheumatoid arthritis may cause a mild form of the symptoms.

Diagnosis of Myositis 

Many conditions that are more common than myositis may cause muscle weakness and pain. Our team may suspect myositis based on your symptoms (muscle weakness) and other factors. We will recommend various tests to determine the causes for your muscle weakness.
  • Blood tests will show whether you have high levels of muscle enzymes, such as creatine kinase, which can indicate inflammation. We may also look for abnormal antibodies to identify autoimmune conditions that may be contributing to your condition.
  • An MRI scan will help us identify which muscles may be experiencing myositis and will allow us to monitor changes in those muscles.
  • We will use an electromyogram (EMG) to test the response of your muscles to electrical nerve signals; this allows us to identify weak or damaged muscles. 
  • A muscle biopsy of a small portion of an identified muscle will help us provide a definitive diagnosis for myositis.

Treatment Options  for Myositis

The first set of treatments for myositis is to resolve or manage the underlying condition. If we cannot determine the cause, we will help you manage the symptoms.
  • For myositis caused by injuries, treating the affected muscle and rest will usually resolve the weakness.
  • If your myositis is caused by a virus, the symptoms will usually pass once the virus has run its course. (In the rare case of a bacterial infection causing myositis, we may recommend antibiotics to stop the spread of the infection.)
  • If medications are determined to be the cause of your myositis, then we will work with your primary physician to find alternatives that do not cause this condition.
  • For myositis caused by inflammation or autoimmune conditions, we may recommend treatment with drugs that suppress the immune system such as prednisone.

If you have experienced a prolonged period of muscle weakness, we may suggest physical therapy and exercise to regain strength in the affected muscles.

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