Myositis 

Myositis refers to any condition that causes muscle inflammation. Polymyositis and dermatomyositis are the two of the most common types. Polymyositis causes muscle weakness in both sides of the body, usually in the hips, thighs, shoulders, upper arms and neck.  Dermatomyositis causes muscle weakness as well as a skin rash. Dermatomyositis in children may differ from that seen in adults.  Myositis affects about 50,000 to 75,000 Americans. 
 

Anything that causes swelling in the muscles – including injury, vigorous exercise, infection or exposure to some viruses (the common cold and flu) – can trigger myositis. Certain medications (such as statins) and illegal drugs (like cocaine) can cause myositis, too.  

Inflammatory types of myositis, like polymyositis and dermatomyositis, are likely the result of an improperly working immune system. The immune system, which is supposed to fight invaders like germs, gets confused and attacks the body’s own cells and tissues instead. Experts still aren’t sure why this happens.  A trigger, like an infection, may jump start the disease process in people who have certain genes.  

Symptoms of myositis usually develop gradually and include  

• Muscle weakness. 
• Muscle swelling. 
• Muscle pain or soreness. 
• Fatigue. 
• Difficulty moving limbs or lifting arms. 
• Falls. 

Polymyositis and dermatomyositis often come with periods of worsening symptoms (flares). In addition to the ones listed above, symptoms may include: 

• Joint pain. 
• Shortness of breath. 
• Trouble swallowing. 
• Fever.  
• Weight loss. 
• Raynaud’s phenomenon (sensitivity to cold with a bluish or white color of the fingertips).  

Dermatomyositis causes patchy purple or red rashes on the face, eyelids, elbows, knees, toes, chest or back. These rashes can appear before, after or during symptoms of muscle weakness. People with dermatomyositis may also be sensitive to light and have hardened, white bumps under the skin (calcinosis).   

There is no cure for myositis, but symptoms can be managed. Treatment includes a combination of medication and lifestyle changes.  

Medications 

Depending on the type of myositis you have, your doctor may prescribe one or all these types of medications: 

• Corticosteroids. Treatment often begins with high doses of corticosteroids to quickly reduce inflammation. These are usually given through injection 
• Immunosuppressive drugs. If corticosteroids don’t relieve symptoms, drugs that suppress the immune system may be prescribed for inflammatory types of myositis. The most common ones used to treat myositis are methotrexate and azathioprine.  
• Immunoglobulin. This purified blood product, which contains healthy antibodies, can help prevent damaging antibodies from attacking the muscles. It is usually given through a vein (intravenously).  

Muscle weakness and fatigue can happen for several reasons, so diagnosis can be a long and challenging process. Often, people with myositis will have symptoms for months and have trouble doing daily tasks (like climbing stairs or rising from chairs) long before they are diagnosed. 

Your doctor will ask questions about your symptoms and family history, perform a physical exam to check for skin symptoms and signs of muscle weakness, and order laboratory or imaging tests to make a diagnosis. The doctor may also perform a biopsy, which involves removing a small sample of muscle tissue to check for signs of inflammation and damage.   

Physical therapy can help build muscle strength, prevent muscle weakness and atrophy, and improve flexibility.