What is myositis?

Myositis is a rare muscle disease that causes muscle weakness. There are different types of the condition.

What is myositis?

Myositis is the collective name given to a rare group of diseases known as the inflammatory myopathies.

These are a group of diseases, with no known cause, that involve chronic muscle inflammation accompanied by muscle weakness.

This includes dermatomyositis, juvenile dermatomyositis, polymyositis and inclusion body myositis. Within these there can also be further complications, such as myositis antisynthetase syndrome.

Collectively these diseases are more commonly referred to as myositis because they all cause inflammation of the muscles and connective tissues (‘myo’ means muscle and ‘itis’ means inflammation).

The main symptom is muscle weakness which may be progressive and can be severely disabling. In most people myositis starts very gradually – the first signs might be an unusual rash or tripping and falling more regularly.

In polymyositis, the condition affects many areas (‘poly’ means many). In dermatomyositis the problems are similar to polymyositis but also include skin rashes (‘derma’ means skin). Inclusion body myositis is usually progressive and difficult to treat.

These are all rare diseases. Polymyositis and dermatomyositis affect only 6–8 people out of 100,000. They mostly affect adults, although children can be affected by a type of dermatomyositis (juvenile dermatomyositis). Inclusion body myositis is the most common acquired muscle disease in people over 50, but it is still a rare disease.

All types of myositis can be accompanied by pain, depression and feelings of unhappiness.

What causes myositis?

The definitive cause is unknown, but both genetic predisposition and environmental factors are thought to play a part.

Dermatomyositis, polymyositis and juvenile dermatomyositis are thought to be autoimmune diseases. This is where the immune system attacks the body’s own tissues, in these cases the muscles, leading to persistent and chronic inflammation.

The cause of inclusion body myositis is speculative and may involve both autoimmune and degenerative processes.

Myositis can affect people of any age and there is no way to predict who will be affected by it.

More about myositis conditions

Is there a cure?

There is no cure but most types of myositis can be treated using steroids and immunosuppressant medication. Unfortunately inclusion body myositis is unresponsive to current treatment and is often a case of adapting to live and cope with the disease.

More about treatments and therapies

Where next?

Types of myositis

Find out more

Recently diagnosed

Find support

Living with myositis

Ways to cope
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