Polymyositis (PM) is a form of myositis – a rare disease that causes muscle weakness and inflammation in adults.

What is polymyositis?

Polymyositis (PM) is a rare disease that causes chronic muscle inflammation and weakness. It affects the muscles and connective tissues of the body, and sometimes the joints too.

The main symptoms are weakness and inflammation of the muscles (‘poly’ means many, ‘myo’ means muscle, and ‘itis’ means inflammation). The muscular weakness may be progressive and can be severely disabling.

Who gets polymyositis and at what age?

Polymyositis can affect people of any age and gender. It affects about twice as many females as males.

What causes polymyositis?

We do not know what causes polymyositis. Like all types of myositis, it is thought to be down to a number of factors both genetic and environmental, and nothing a particular individual has done themselves. Many doctors and researchers worldwide are looking into the cause of myositis.

Most think that myositis is an autoimmune disease. This means that the disease is a result of a defect in the immune system, which is the body’s natural defence against disease. In healthy people, the immune system fights infection by producing substances to attack bacteria and viruses. In people with an autoimmune disease, the defect causes the immune system to turn against the body and attack it’s own tissues, blood vessels, fibres or joints.

Others feel myositis may be started by a virus or the combination of a viral infection and defective immune system.

What are the symptoms of polymyositis?

The main symptoms of polymyositis are weak and painful muscles, tiredness and feelings of depression. Some people may also have joint pains.

Some may have the disease for months or even years before it is realised, but most notice within weeks if they have developed muscular weakness.

Weak and tender/painful muscles

The large muscles about the hips and shoulders are usually the first to be affected and may feel tender and weak. This is caused by the swelling of the blood vessels in the muscles (vasculitis).

The weakness results in difficulty in walking, lifting arms and getting up from the sitting and lying down positions. There may even be some trouble in swallowing and the voice may become nasal or deeper in quality.

Other muscles sometimes affected are those in the neck, making it difficult to raise the head when lying down.

Feelings of depression

Depression and a general feeling of unhappiness is very noticeable and can be an indication of the disease before any sign of muscle weakness.

Other symptoms

Other possible symptoms of the illnesses include fever and weight loss.

How is polymyositis different from other types of myositis?

Polymyositis, while defined as an inflammation of the muscles, can also be a feature of a more general autoimmune illness such as systemic lupus erythematosus, scleroderma or even rheumatoid arthritis.

A few people have an extreme sensitivity and reaction to cold called Raynaud’s phenomenon which is most often felt in the fingers and toes and is caused by a spasm of the blood vessels.

This reduces blood flow and turns the fingers and toes white, then gradually to blue. They may also feel numb and may develop shiny red areas around and under the nails. In this situation it is very important to keep hands and feet warm.

Can I catch polymyositis from other people?

No, there is no evidence to suggest that polymyositis can be transmitted to other people as an infection. The disease is also not inherited and as yet there is no way one can predict who in the general population will be affected.

How is polymyositis diagnosed?

Experienced doctors at a centre familiar to the disease will recognise myositis after a simple examination. It will then need to be confirmed by  a combination of blood tests and other tests such as electromyography and muscle biopsies.


When muscles are damaged they release creatine kinase (CK) and lactate dehydrogenase (LDH) enzymes into the bloodstream. These can be tested for in a routine blood sample. Blood tests alone will not confirm but are a useful starting point.

Electromyography (EMG)

An examination of the electrical activity of the muscle, known as electromyography, may be helpful in making a diagnosis.

When healthy muscles contract, they fire off a co-ordinated pattern of electrical impulses that can be detected by a tiny needle positioned in the muscle. When sick muscles contract, abnormal electrical impulses can be detected.

Muscle biopsy

A muscle biopsy involves a small piece of muscle tissue being taken (usually under local anaesthetic) and then examined under a microscope.

Laboratory analysis includes a series of stains and reactions, used to highlight different parts of the muscle and look for damaged cells.

What is the treatment for polymyositis?

There is no cure for polymyositis yet, but there are treatment options to help manage the symptoms.


Once the disease has been diagnosed, most patients respond well to steroids.


A second line of treatment is immunosuppressive medication. Like steroids, these drugs suppress the body’s immune system and limit the inflammation. These drugs are monitored under a strict regime, with regular blood tests to monitor their effect and progress.


If the patient does not respond to these treatments then intermittent (pulsed) treatment can be given intravenously or plasma exchanges would be considered.

Find out more about treatments and therapies.

What else can make polymyositis better?

In addition to medication, exercise and physiotherapy can help ease the symptoms of polyyositis.


Exercise is encouraged even in early phases of the condition, guided by your doctor and physiotherapist. They will give you exercises to help restore muscle strength


Appropriate physiotherapy exercises can help to maximise the efficiency of the relatively unaffected muscles. Together with medical treatment, physiotherapy can also help make weak muscles strong again. Whether they return to full strength depends on many factors such as age at onset of disease.

Find out more about treatments and therapies.

If the disease goes away, will it come back?

There is always a possibility that this can happen. As it is not fully understood how polymyositis develops initially, it can be triggered again.

In women there is always a slight chance that there could be a flare up because of hormonal changes particularly in pregnancy and a medical opinion should be sought before this is envisaged. This can also apply when deciding to take oral contraception.

What does a future with polymyositis look like?

A small percentage do get well within two years. For most it is a case of living with the disease and understanding as much about the illness as possible, so that even during the periods of increased pain and weakness, a nearly normal life can be led.

It cannot be denied that it is a chronic illness but the disease is rarely fatal, and as long as the prescribed medication is taken, the future is always hopeful.

Will I end up in a wheelchair?

Some patients may well need a wheelchair from time to time to help them stay active and mobile. Other equipment may be needed while the illness is at its height. A rare few may need more permanent help if there is serious damage of the muscles.

Where next?

Recently diagnosed

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Types of myositis

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Treatments and therapies

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