What is myositis?

Myositis is the name for a group of rare conditions that can cause muscles to become weak, tired and painful.

The word myositis simply means inflammation in muscles. If something is inflamed, it may be swollen.

Myositis can affect people of any age, including children.

The main muscles to be affected are around the shoulders, hips and thighs.

Having myositis can also lead to other parts of the body being affected, such as the skin, lungs or heart.

Sometimes myositis can affect the muscles that carry out tasks such as breathing and swallowing.

There are several types of myositis. The two most common types are polymyositis and dermatomyositis.

‘Poly’ means many. Polymyositis means that many muscles are affected by inflammation. This type doesn’t often affect other parts of the body much.

Dermatomyositis causes similar symptoms in muscles, but there is also a skin rash. ‘Derma’ means skin.

Polymyositis, dermatomyositis, as well as other types of myositis, are autoimmune conditions.

The immune system is the body’s natural self-defence system. When healthy, it protects us from infection, injury and illness.

However, in people who have autoimmune conditions, the immune system gets confused and mistakenly attacks the body’s own healthy tissues.

One feature of a healthy immune system is inflammation. For example, when we have a cut, the body sends fluid to the affected area so that white blood cells can fight off any infection.

If someone has an autoimmune condition the body can create inflammation when there is no infection to fight. The unnecessary inflammation can then cause problems.


The symptoms of myositis vary between different people.

They can include:

  • weak and tired muscles that can make everyday tasks such as climbing stairs, brushing hair, and getting in and out of cars difficult
  • pain in muscles
  • muscles feeling tender to touch
  • muscles can sometimes swell
  • generally feeling unwell
  • weight loss
  • night sweats.

The most common muscles to be affected are around the shoulders, hips and thighs.

The weakening and tiredness in the muscles can make people with myositis more likely to fall over.

With dermatomyositis you can have the above symptoms as well as:

  • a red or pink rash on the upper eyelids, face and neck, and on the backs of the hands and fingers
  • swelling of the affected skin
  • puffiness and colouring around the eyes.

Some other medical conditions can appear similar to myositis. These include:

  • the side effects of some medications – for example, steroids and drugs to lower your cholesterol levels, such as statins
  • effects of drinking too much alcohol over a long period
  • hormonal conditions – for example, under- or overactive thyroid glands
  • low vitamin D levels
  • abnormal calcium or magnesium levels
  • infections
  • other rare muscle conditions – for example, where muscles waste away.

Other types of myositis

Polymyositis and dermatomyositis are the two main types of myositis. Here are some of the others:

Inclusion body myositis (IBM)

Inclusion body myositis (IBM) causes weakness in muscles, usually near the ends of the arms or around the tops of the legs. This can make it difficult to grip objects, or can cause the knee to give way and lead to falls. This condition can also make swallowing difficult.

The effects can happen slowly over 10 to 15 years. It affects more men than women, and generally starts once people are over the age of 50.

The key difference in inclusion body myositis compared to other types of myositis is that as well as inflammation in the muscles, there is also a build-up of protein. These tiny clumps of protein can only be seen with special microscopes. They might not be seen clearly in the early stages of the condition. And so it can be difficult to tell the difference between polymyositis and inclusion body myositis.

Inclusion body myositis doesn’t respond to steroids or disease modifying anti-rheumatic drugs (DMARDS), that are used to treat other types of myositis. It’s thought that this resistance to treatment is related to the clumps of protein in the muscle cells, which the body cannot break down.

If you’re diagnosed with polymyositis and steroids aren’t working, you may need further tests to look more closely for inclusion body myositis.

While there are no effective drugs for inclusion body myositis, the following can really help:

Anti-synthetase syndrome

Anti-synthetase syndrome is a condition where several parts of the body are affected by inflammation.

It can affect the muscles, and elsewhere, such as the lungs and skin. This lung condition can potentially be serious, which is why prompt medical treatment is important. Early symptoms can be a dry cough, which can occur before skin and muscle symptoms.

People with anti-synthetase syndrome might also have a condition called Raynaud’s phenomenon. In this condition the fingers and toes change colour when cold. They may turn white, then blue and feel very cold to touch. When they warm up again, the fingers and toes may go red and start to throb or swell.

Some people with this condition have in the past incorrectly been told that they have polymyositis or dermatomyositis. It has some similar symptoms, but is now being classed as a separate condition.

Immune-mediated necrotising myopathy

This type of myositis has been discovered more recently. It causes muscle cells to rapidly die in a process called necrosis. Weakness is usually very severe and people with this condition will often struggle to walk and use their arms. In extremely rare cases, this condition can be triggered by statin medication.

Post-infectious reactive myositis

Infectious or post-infectious reactive myositis can occur during and after some viral infections. Even after the virus has gone, the immune system may cause inflammation in some parts of the body for a few months.

Symptoms are similar to those of polymyositis, such as muscle pain and weakness. Usually, the condition is mild and can settle without treatment.

In rare cases, some people who have HIV infection can develop long-term viral muscle infections.

Drug-induced myopathies

Drug-induced myopathies can sometimes appear like myositis. The most common drugs to cause this are statins used to lower people’s cholesterol levels. Usually, stopping this drug treatment leads to improvement in symptoms. Occasionally, the symptoms can last after the drug treatment has been stopped and people can develop myositis.

How will myositis affect me?

In most cases the pain and feelings of being unwell are eased with drugs. Even in severe cases most people with myositis eventually respond to treatment.

You may need to try more than one treatment before you find the right one for you.

Muscle strength can take longer to get back to normal. Once myositis is controlled with treatment, exercises can also help to improve muscle strength.

Although people can make a good recovery, some never regain their original muscle strength or function.


Sometimes, drug treatments don’t work fully and the muscles can remain weak. We are still doing research into why this is the case.

Occasionally, myositis can affect breathing and swallowing. This may occur at the start of severe cases when the muscles used for these important tasks become weak.

On rare occasions, this condition may cause weakening of the heart.

If there is inflammation in the lungs this can cause scarring, which can affect how the lungs work.

Lung and heart conditions can cause long-term breathlessness. For this reason, you may be referred to a heart or chest specialist if there’s a risk of these problems developing.

Children with dermatomyositis may develop painful deposits of the mineral calcium in damaged muscles. These deposits, combined with loss of mobility, can occasionally result in permanently rigid joints, which are called contractures.

Polymyositis occasionally occurs in patients who have other autoimmune conditions such as rheumatoid arthritis, lupus or scleroderma.

On rare occasions, myositis can be associated with cancer. Most people with myositis don’t develop cancer, but your doctor might arrange tests such as a chest x-ray or an ultrasound scan of your abdomen and pelvis to be on the safe side.


There is no single test that can show for certain if someone has myositis.

Your doctor will talk to you about your symptoms and examine you.

Because the symptoms of myositis are similar to many other conditions you’ll probably have blood tests and other examinations.

Blood tests

Blood tests can look for:

  • signs of damaged muscles
  • inflammation levels within the body
  • the presence of autoantibodies, which are tiny proteins that can attack the body’s own healthy tissues and cells.

There is no autoantibody test that can prove for certain you have myositis, but there are tests that can be helpful in making a diagnosis.

One of these is the anti-nuclear antibody test (ANA). This is a test to see if your blood has antibodies that attack the central part of a cell called the nucleus.

Healthy people can also test positive so it’s only helpful alongside all the other information about your symptoms.

Other autoantibody tests include ENA (extractable nuclear antigens) and the anti-Jo-1 test. These tests are sometimes positive in people with myositis.

There are now lots of different autoantibodies which can be present in people with myositis. Tests for these can sometimes be useful for predicting your responses to treatment.

Even if these tests haven’t led to a diagnosis of myositis, they may have helped your doctor rule out other conditions. There are other tests to help confirm a myositis diagnosis.


You may have a test called electromyography (EMG). This involves a tiny needle electrode, being inserted into the muscle to record electrical messages from nerve endings that enable your muscles to move.

An unusual pattern of electrical activity in a number of different muscles can be due to myositis. The test isn’t very painful but may be uncomfortable.

Muscle biopsy

A small sample of your muscle may be taken from one of your larger muscles, for example at the side of your thigh or calf, and examined under a microscope to look for signs of inflammation. This is called a biopsy.

You’ll be given a local anaesthetic to numb the area while the sample is taken, but there may be some discomfort for a few days afterwards.

Sometimes, you may need to have another muscle biopsy if your condition doesn’t improve with standard treatments. This is to check for the proteins found in inclusion body myositis.

Magnetic resonance imaging (MRI)

An MRI scan can help work out where the inflammation is. Sometimes MRI scans can pick up areas of muscle that are being replaced by fat, indicating damage.

An MRI is a scan that uses magnets to look at what is happening inside your body. It can show soft-tissue damage – in the muscles, ligaments or nerves – as well as any problems with the bones.


Treatment for myositis includes a combination of drug treatment and exercise.


The first choice of treatment of myositis is steroids, which are usually given in high doses to begin with.

Steroids can be given as tablets or injections. They should reduce the inflammation quickly, settle muscle pain and the feeling of being unwell.

High doses of steroids can have side effects, so your doctor will reduce the dosage as quickly as possible.

Taking steroids over a long time can increase the risk of developing the condition osteoporosis, which causes bones to become thin and fracture more easily. There are drugs you can take alongside steroids to reduce the risk of developing osteoporosis. This includes bisphosphonates, which can slow bone loss.

Sometimes the symptoms of myositis can flare up when the steroid dose is lowered and your doctor may often prescribe other drugs to help reduce the inflammation. These include methotrexate, azathioprine, ciclosporin, tacrolimus and mycophenolate.

Most of these are types of disease-modifying anti-rheumatic drugs (DMARDs), and you will need regular blood tests to check for possible side effects.

Occasionally these drugs aren’t able to control myositis. In these more severe cases, the following drugs might be available:

Biological therapies work by blocking specific targets within the immune system that cause inflammation.

Immunoglobulins are antibodies collected from blood donations given by healthy people, which can help stop your immune system from attacking your own tissues. This treatment is usually given as a drip into a vein in your arm, known as an intravenous drip. This will be carried out in hospital and it can be repeated if needed. Sometimes you might feel a little unwell, during the treatment itself.

Even in severe cases, myositis usually responds to treatment, although many people need life-long drug treatment to keep their condition under control.

Exercise and physiotherapy

It’s probably best to rest when your myositis is very active, but once it has calmed down doing regular exercise can greatly improve your symptoms and overall health.

Aerobic exercise, which makes you breathe more heavily and your heart beat faster, is especially important to help restore muscle strength and improve stamina.

At first this should ideally be done under the supervision of a physiotherapist, who’ll give you a tailored programme. You should avoid very strenuous exercise.

Children with juvenile dermatomyositis will need more vigorous physiotherapy to reduce the risk of joints, especially the knees, becoming permanently bent.

People with myositis can make a good recovery. However, some people with severe symptoms may never fully recover.

Even for people who do make a good recovery it can take several months to see improvement, as treatments take time to help your body repair muscles. Because of this you may experience a lot of tiredness.

Continuing to exercise as regularly as you can will greatly help with many aspects of your condition.

Research and new developments

Versus Arthritis has funded multiple research studies to further our understanding of myositis.

We’ve funded research to look at the link between genes people inherit, the presence of certain antibodies and the severity of their condition. This will allow doctors to predict which patients will experience mild or severe disease and why. This will help identify targets for future drug development.

We’ve also funded research to develop a standard method of assessing children with suspected juvenile dermatomyositis to improve diagnostic techniques, treatment and outcomes for young people. As these conditions are rare, research centres are joining forces to aid recruitment to clinical trials.

We are currently supporting several studies into juvenile dermatomyositis at our centre for adolescent rheumatology at Great Ormond Street Hospital, in London.

This research includes a study looking at the role of a specific white blood cell, a B cell, in myositis. Blood samples will be taken from young people with juvenile dermatomyositis and a group without the condition. The information gathered will improve our knowledge of the condition and may help to develop new and more effective treatments in the future.