Myositis

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Overview

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.

Symptoms

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.

Causes

Your nerves communicate with your muscles by releasing chemicals (neurotransmitters) that fit precisely into receptor sites on the muscle cells at the nerve-muscle junction.

In myasthenia gravis, your immune system produces antibodies that block or destroy many of your muscles' receptor sites for a neurotransmitter called acetylcholine (as-uh-teel-KOH-leen). With fewer receptor sites available, your muscles receive fewer nerve signals, resulting in weakness.

Antibodies can also block the function of a protein called muscle-specific receptor tyrosine kinase (TIE-roh-seen KIE-nays), sometimes referred to as MuSK. This protein is involved in forming the nerve-muscle junction. Antibodies against this protein can lead to myasthenia gravis. Antibodies against another protein, called lipoprotein-related protein 4 (LRP4), can play a part in the development of this condition. Other antibodies have been reported in research studies and the number of antibodies involved will likely expand over time. Some people have myasthenia gravis that isn't caused by antibodies blocking acetylcholine, MuSK or LRP4. This type of myasthenia gravis is called seronegative myasthenia gravis or antibody-negative myasthenia gravis. In general, researchers assume that these types of myasthenia gravis still have an autoimmune basis but the antibodies involved are just not detectable yet.

Thymus gland

The thymus gland is a part of your immune system situated in the upper chest beneath your breastbone. Researchers believe that the thymus gland triggers or maintains the production of the antibodies that block acetylcholine.

Large in infancy, the thymus gland is small in healthy adults. In some adults with myasthenia gravis, however, the thymus gland is abnormally large. Some people with myasthenia gravis also have tumors of the thymus gland (thymomas). Usually, thymomas aren't cancerous (malignant), but they can become cancerous.

Other causes

Rarely, mothers with myasthenia gravis have children who are born with myasthenia gravis (neonatal myasthenia gravis). If treated promptly, children generally recover within two months after birth.

Risk factors

Fatigue

Illness or infection

Surgery

Stress

Some medications — such as beta blockers, quinidine gluconate, quinidine sulfate, quinine (Qualaquin), phenytoin, certain anesthetics and some antibiotics

Pregnancy

Menstrual periods

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Complications

Complications of myasthenia gravis are treatable, but some can be life-threatening.

Myasthenic crisis

Myasthenic crisis is a life-threatening condition that occurs when the muscles that control breathing become too weak to work. Emergency treatment and mechanical assistance with breathing are needed. Medications and blood-filtering therapies help people to again breathe on their own.

Thymus gland tumors

Some people with myasthenia gravis have a tumor in the thymus gland, a gland under the breastbone that is involved with the immune system. Most of these tumors, called thymomas, aren't cancerous (malignant).

Other disorders

People with myasthenia gravis are more likely to have the following conditions:

Underactive or overactive thyroid. The thyroid gland, which is in the neck, secretes hormones that regulate your metabolism. If your thyroid is underactive, you might have difficulties dealing with cold, weight gain and other issues. An overactive thyroid can cause difficulties dealing with heat, weight loss and other issues.

Autoimmune conditions. People with myasthenia gravis might be more likely to have autoimmune conditions, such as rheumatoid arthritis or lupus.

Prevention

After drug treatment takes effect, a program of regular stretching exercises prescribed by your doctor can help maintain range of motion in weakened arms and legs. Physical therapy may also help prevent permanent muscle shortening. You may also want to add whirlpool baths, heat and gentle massage.

Like other rheumatic diseases, myositis is unlikely to go away on its own. But with proper treatment and management these chronic diseases can be brought under control. At present there is no cure for myositis. A person with myositis will need to manage the condition and to adjust to the changes it brings.