What are inflammatory muscle diseases?

Inflammation is the process by which our immune system reacts to infections and tissue damage. In inflammatory muscle diseases, the immune system reacts against healthy muscles thereby causing damage to muscle fibres.

Polymyositis and dermatomyositis are the two major types of inflammatory muscle diseases. Most noticeable feature of these diseases is muscle weakness. Muscles in the hip and shoulder are particularly affected. This can cause difficulty in climbing stairs, rising from a chair or brushing your hair.

They are both rare conditions. Doctors see about one new patient per 100,000 population each year.

Who can get inflammatory muscle diseases?

Polymyositis can occur at any age. However, adults in their 40s and 50s are most commonly affected and more women are affected than men.

Dermatomyositis too can occur at any age but mostly affects adults between 40 and 60. Children between ages of 5 and 15 can also get it but this is distinct from the adult form.

What causes it?

Polymyositis and dermatomyositis are both believed to be autoimmune conditions in which our body’s immune system attacks healthy components of our body mistaking them for foreign substances.

The cause is unknown but it is believed that a combination of environmental and genetic factors is responsible.

In polymyositis, there is direct damage to muscle fibres mediated by cells in our immune system.

In dermatomyositis, small blood vessels in muscles are particularly affected. Destruction of the blood vessels causes the degeneration of muscle fibres.

What are the symptoms?

The most common features of polymyositis are:

• Weakness in muscles closest to the trunk of the body such as those in hips, thighs, shoulders and neck which develops slowly over weeks or months
  
• Fatigue
  
• Joint or muscle tenderness
  
• Due to the muscle weakness, some people may experience difficulty with
  
  
  
  • Climbing stairs
    
  • Rising from a chair
    
  • Brushing hair
    
  • Lifting your head up from the pillow
    
  • Swallowing
    
  • Taking a deep breath
    
  
  

In addition to the above features, individuals with dermatomyositis frequently get a violet or dusky-red rash usually on eyelids, face, knuckles, elbows, chest and back

The skin rash can precede the muscle weakness by a few weeks or occur independently.

Grassi W. Department of Rheumatology, University of Ancona, Italy

What are the complications?

It is important to note that the complications described below do not occur in everyone with inflammatory muscle diseases. It is however important to monitor patients for these.

• Lungs: Some patients can develop lung disease where inflammation and scarring of lung tissue make lungs stiff and inelastic. Symptoms include a dry cough and shortness of breath. As a late complication, high blood pressure in the blood vessels in the lung (pulmonary hypertension) can develop. Weakness in muscles that aid inspiration and expiration can cause breathing difficulties.

  
  

• Heart: Rarely, inflammation of the heart muscles can occur. This may cause palpitations, a sensation of the heart beating.

  
  

• Gut: Difficulty in swallowing may occur due to abnormalities of movement in the oesophagus. In the childhood form of dermatomyositis, bleeding in the bowels can occur.

  
  

• Cancer: Dermatomyositis may be associated with increased risk of malignancy in older patients but this risk is often overestimated. Malignancies which may be associated with dermatomyositis include tumours in the lung, oesophagus, breast, colon and ovary and lymphomas.

  
  

Your doctor may have screened you for these complications using tests such as CT scans, x-rays, lung function tests and blood tests. It is advisable to keep up to date with all screening tests such as cervical smears and mammograms.

How is it diagnosed?

The following criteria are widely used for diagnosis:

• Symmetrical weakness of muscles close to the trunk of the body developing over weeks to months
  
• A rise in the blood level of certain enzymes found in muscles (creatine kinase, aldolase)
  
• Typical findings in electromygraphical studies: Electrical activity in muscles is measured as you relax and tighten them. There are patterns typical of particular diseases.
  
• Muscle biopsy findings: A small piece of muscle tissue is tissue is surgically removed to analyze for signs of inflammation.
  
• Skin changes typical of dermatomyositis:
  
  
  
  • Scaly red rash over knuckles, knees and elbows (Gottron’s sign)
    
  • Violet, dusky-red rash over eyelids (Heliotrope sign)
    

Other diagnostic findings include:

• Autoantibodies (proteins produced by our immune system that react against our own body tissues) specific to inflammatory muscle diseases (Anti-nuclear antibody, anti Jo-1).
  
• Typical findings in magnetic resonance imaging (MRI) scans.
  

How is it monitored?

• Periodic testing of muscle strength gives an objective measure of the progression of the disease. Muscle strength is measured by performing a few simple exercises on a specialised exercise machine at the hospital.

• Creatine kinase levels are useful in gauging disease activity but do not correlate particularly well with the severity of the disease.

  
  

How is it treated?

• Corticosteroids: Corticosteroids such as prednisolone are the first choice in treating inflammatory muscle diseases. Usually treatment is started with a high dose and is gradually reduced as symptoms improve. It may take three to six months for a significant improvement and it may be necessary to be on therapy for years. However, prolonged use of corticosteroids can give serious side effects such as brittle bones (osteoporosis), diabetes, muscle weakness and cataracts. Hence, your doctor my recommend supplements such as vitamin D and calcium and medication that protects bones.

  
  

• Immunosuppressants: Medicines such as azathioprine, methotrexate or mycophenolate mofetil may be used if the response to corticosteroids is inadequate or in order to reduce the dose of corticosteroids used.

  
  

• Physical therapy: Exercises which improve muscle strength and flexibility are a useful adjunct to drugs. Gentle exercise which increases your heart rate such as swimming and cycling are more beneficial than weight training.

  
  

What is juvenile dermatomyositis?

Juvenile dermatomyositis causes a rash and weak muscles in children. It is different from adult dermatomyositis and polymyositis. The skin rash and the weakness in muscles are due to inflammation in blood vessels. Blood vessels in other areas of the body such as the gut may also be affected.

It is important to realise that juvenile dermatomyositis is not contagious. It is an autoimmune disease in which the body’s immune system reacts against our own healthy tissues. The cause is unknown.

Some children may have calcium deposits in muscles or contractures where muscles shorten and joints stay bent. Exercising helps avoid contractures. Other symptoms include weak voice, difficulty swallowing and pain in muscles.

Treatment is similar to that in adult dermatomyositis and polymyositis.

How can I help myself?

• Find out more about the illness: Having a greater understanding about the condition and asking your doctor about the diagnosis and treatment will help you cope. Also talk to people with the condition.
  
• Exercise: A suitable exercise plan is provided which will help build strength in muscles in shoulders and hips. Regularly perform the physical exercises prescribed to you. It is important that you learn to pace yourself and rest before you get tired. Ask for help when needed.
  
• Emotions: It is normal to feel anger and frustration when dealing with a chronic illness. Feelings of fear and isolation are also common. Being close to your family and friends and maintaining your daily routine as much as possible will help deal with such emotions.
  

What resources are available?

Some find it helpful to get in touch with others with similar disease and to share experiences.

Myositis Support Group

Exercise Referral Schemes are exercise schemes run by fully-qualified professionals that are tailor-made to improve your health in a safe and effective way. Your GP can refer you onto such schemes.

• "Startup" is an exercise referral scheme run jointly by Cambridge City Council, South Cambridgeshire District Council and the Cambridge City and South Cambridgeshire Primary Care Trust. For further information phone (01223) 415151 or visit their website.
  

COMMON LINKS

Lung function tests

Lung function tests evaluate how well your lungs work. They measure how much air your lungs can hold, how quickly you can move air in and out of your lungs and how well the lungs exchange gases such as oxygen and carbon dioxide with air. They provide information that help diagnose lung diseases and measure severity of lung problems.

For most lung function tests, you will be asked to breathe into a mouthpiece connected to a computer (spirometer). They present little or no risk to a healthy person.

Residual volume, or the amount of air that remains in your lungs after you exhale as completely as possible, is measured with gas dilution tests. You breathe a known amount of a gas from a container. The test measures how the concentration of the gases in the container changes.
Gas diffusion tests measure the amount of oxygen and other gases that cross the lung’s air sacs per minute. They evaluate how well gases are being absorbed into your blood from your lungs.

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These pages have been prepared by clinical student Udara Kularatne, in conjunction with members of the Rheumatology department

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