Myositis is a condition that causes inflammation of the muscles. There are different types of myositis, which may be the result of an infection, injury, medication, or autoimmune disease.
Read on to learn more about myositis, including the definition, symptoms, treatments, and outlook.
Myositis is a group of conditions that share the common feature of chronic muscle inflammation, resulting in muscle weakness and damage.
There are different types of myositis, as follows:
Polymyositis (PM) is a rare disease that affects proximal, or core, muscles, such as the back, hips, and neck.
This muscle weakness can appear in a matter of days or become apparent over several months.
People with PM often have other autoimmune diseases.
PM affects fewer than 200,000 people in the United States.
Dermatomyositis (DM) also affects the proximal muscles. However, DM causes skin rashes and other skin-related symptoms as well.
DM is another rare condition that affects fewer than 200,000 people in the U.S.
Juvenile myositis (JM) affects children younger than 18 years of age. The condition includes juvenile polymyositis (JPM) and juvenile dermatomyositis (JDM).
JPM causes inflammation in the muscles, whereas JDM results in the inflammation in blood vessels. Doctors diagnose around 1,000 children with JM each year in the U.S.
Immune-mediated necrotizing myositis
Immune-mediated necrotizing myositis (IMNM) is also known as necrotizing autoimmune myopathy. It has similar symptoms to PM, but IMNM causes necrosis, or muscle cell death.
Necrosis can lead to severe muscle weakness on both sides of the body. An estimated 6,300 people in the U.S. have this type of myositis.
In some cases, the cause of IMNM may be due to using certain medications, such as statins.
Inclusion body myositis
Inclusion body myositis (IBM) causes progressive muscle atrophy and weakness that may affect one side of the body more than the other.
IBM most commonly affects people of 50 years of age and older. IBM affects an estimated 30,000 people in the U.S. and Europe combined.
Infectious myositis (IM) is a form of myositis that is the result of bacterial, fungal, parasitic, or viral factors.
Scientists thought that this type of myositis only affected tropical countries, but there is growing evidence that it also affects people in other countries.
Scientists do not know exactly what causes myositis. Researchers have suggested that genetic and environmental factors may play a role.
Some environmental factors may include:
- UV radiation
- recreational drugs
- dietary supplements
- exposure to dust, gas, or fumes
One study suggests people may find that their conditions improve after avoiding these risk factors and worsen or reoccur after being reexposed.
The same study suggests that certain risk factors may increase the likelihood of specific types of myositis.
The symptoms of myositis vary depending on the type:
Polymyositis and juvenile polymyositis
Besides muscle inflammation and weakness, PM and JPM symptoms may include:
- difficulty swallowing, or dysphasia
- difficulty speaking
- joint pain
- shortness of breath
- heart arrhythmia
Dermatomyositis and juvenile dermatomyositis
In addition to muscle inflammation and weakness, DM and JDM symptoms may include:
- red or violet bumps called Gottron papules on the outside of hands and fingers
- swelling around the eyes
- purple-red rashes sometimes in the shape of heliotrope flower
- redness around the nailbeds
- weight loss
- calcium deposits under the skin
In some cases, a doctor may suggest an age-appropriate screening test to rule out an underlying cancer.
Immune-mediating necrotizing myositis
IMNM has similar symptoms to PM. However, this type of myositis progresses far more quickly and with more severe symptoms.
Swallowing difficulties can also occur with IMNM.
Inclusion body myositis
Unlike other forms of myositis, IBM does not affect both sides of the body at the same time. People may notice muscle weakness in just one leg or arm.
IBM takes longer to progress than other forms of myositis, but the muscles atrophy, or wasting, is worse with this type of myositis than others.
Other symptoms of IBM can include:
- trouble swallowing
- decrease in reflex response
- nerve damage
In addition to muscle inflammation and weakness, IM symptoms may include:
- runny nose
A doctor may order a series of tests to determine whether a person has myositis. These tests can also help to diagnose which type of myositis may be occurring.
Tests will typically investigate the level of enzymes, such as serum creatine kinase. They may also look for antibodies, such as myositis specific antibodies, present in the body.
Doctors sometimes use MRI scans as well.
However, a muscle biopsy remains the gold standard for diagnosing myositis.
The treatment for myositis centers on medications but may vary, according to which type of disease a doctor diagnoses.
Corticosteroids and immunosuppressive drugs
The most common form of treatment for most types of myositis are corticosteroids and immunosuppressive drugs. Doctors may prescribe corticosteroids and immunosuppressants together.
The most common corticosteroids for myositis are prednisone and dexamethasone.
The most popular immunosuppressive drugs are methotrexate, azathioprine, and mycophenolate mofetil.
A biologic medication, rituximab, may also be an option.
Treatment for inclusion body myositis
IBM is often resistant to corticosteroids and immunosuppressive drugs. A treatment called alemtuzumab may be effective.
Alemtuzumab is an antibody that slows down IBM and improves muscle strength.
Treatment for infectious myositis
Treating IM depends on the severity of the condition. Some people may respond well to oral antibiotics, such as cloxacillin. Others may need intravenous antibiotics and secondary treatment, such as draining abscesses.
If a person does not receive treatment, it may lead to sepsis.
Other treatment options
It is essential to see a doctor if a person presents symptoms of myositis.
A doctor can investigate and diagnose which type of myositis a person may be experiencing. They will then decide the appropriate treatment for each case.
Myositis is a serious health condition. There is currently no cure, and people could require a cane or wheelchair if they do not start treatment early. If left untreated, myositis can be fatal.
However, some people respond well to treatment and are able to manage their symptoms. According to a 2016 review, people who received treatment had a 70% 5–year survival rate.
Myositis is a condition that affects the muscles in the body. There are different types of myositis, and the symptoms vary.
Scientists are not sure exactly what causes myositis. However, they believe that environmental and genetic risk factors increase the risk of it occurring.
Treatment for myositis is varied, and doctors may try different drugs to tailor to the individual. It is essential to see a doctor if any symptoms of myositis appear.