Inflammatory Muscle Diseases

Inflammatory Muscle Diseases

Inflammatory muscle diseases (often referred to as “inflammatory myopathies” or “myositis”) are a group of muscle diseases characterized by chronic muscle inflammation, inflammation of tissues associated with the muscles, muscle weakness, and occasionally muscle pain (depending on the specific case). 

What are myopathies?

“Myopathy” is a medical umbrella term that describes muscle diseases, including inflammatory myopathies (or inflammatory muscle diseases). The word “myopathy” quite literally means ‘muscle inflammation’. (“Myo” means ‘muscle’ and “itis” means ‘inflammation’.) 

There are four main types of chronic inflammatory myopathies:

Polymyositis

Polymyositis is an inflammatory myopathy that affects the skeletal muscles responsible for movement. When this disease is present, the inflammatory cells are misfiring and directly targeting the muscle fibers. Polymyositis is found in women more often than men.

Dermatomyositis

Dermatomyositis is another inflammatory myopathy that attacks the blood vessels responsible for transferring blood to the muscles and the skin. This disorder causes skin rashes and progressive muscle weakness and is most commonly found in women and children.

Inclusion Body Myositis

Inclusion body myositis is an inflammatory disease, but also a degenerative muscle disease. When inclusion body myositis is present, a person experiences muscle weakness and muscle shrinkage as the muscles degenerate (or deteriorate). This disease is most commonly found in people over the age of 50.

Necrotizing Autoimmune Myopathy

Necrotizing autoimmune myopathy (an inflammatory myopathy) causes weakness around areas in the upper and lower body. People who have this disorder often experience dizziness, fatigue and muscle pain when climbing stairs or standing up quickly. 

General Symptoms of Myopathies

The four chronic inflammatory myopathies can affect both adults and children. The general symptoms of these diseases include:

Myopathies are rare and typically aren’t life-threatening. There are also effective treatment methods available to help improve muscle functionality and mitigate unpleasant symptoms of most myopathies.

What causes myopathies?

Autoimmune disorders are caused by the body’s immune system attacking other healthy cells within the body. With inflammatory muscle disease specifically, the immune system is attacking the body’s healthy muscle fibers, blood vessels, connective tissues, organs, and joints. 

The immune system misfires, mistaking healthy cells for foreign invaders (like bacteria and infections). The cause behind these autoimmune misfirings in inflammatory myopathies is unknown. Some of the most common autoimmune diseases are type 1 diabetes, rheumatoid arthritis (RA), psoriatic arthritis, multiple sclerosis, systemic lupus erythematosus (SLE), Inflammatory bowel disease, and celiac to name a few. 

Although, the cause behind the inflammatory response is known. Inflammation occurs as a response to autoimmune cell damage; inflammation of the muscles destroys muscle tissue, and over time, can cause complete loss of muscle—called muscle atrophy. 

Inflammation can occur both internally and externally. Inflammation of the muscles isn’t necessarily a sprained ankle or a red, inflamed area on the body (like we see with external inflammation). Inflammatory muscle diseases cause the destruction of the internal organs and tissues. In both cases (internal and external inflammation), inflammatory cells rush to the site of the affected area. 

The cells then release various chemicals, including histamine, bradykinin, and prostaglandins, which cause the blood vessels to release fluid into the tissues, resulting in swelling and inflammation.

Risk Factors of Myopathies

Though the cause of autoimmune diseases is unknown, there are several risk factors that increase a person’s risk of developing this muscle disease.

Due to the rarity of inflammatory myopathies—(polymyositis and dermatomyositis affect about 6 to 8 people out of 100,000 people)—the causes and risk factors of these diseases are still being studied.

These diseases are known to be “idiopathic”, which means the cause is generally unknown, and these diseases can develop spontaneously. This spontaneous development makes it difficult to prevent myopathies.

Pre-Existing Viruses

Having a pre-existing virus is a potential trigger for autoimmune myositis. People with the HIV virus (which causes AIDS) are at a higher risk of developing myositis. People who have the virus HTLV-1 or the Coxsackie B virus are also known to be at a higher risk.

Adverse Reaction to Medications

In several cases, myositis has developed after the use of specific medications or exposure to various drugs, including:

Cancer

An existing myopathy, especially polymyositis or dermatomyositis, places a person at a higher risk of developing cancer. This is because the antibodies produced by the immune system are attacking the body’s healthy tissues—not the cancerous cells. Misfirings allow cancer to develop at a faster rate.

Who is at risk for myopathies?

These diseases can unfortunately affect anyone, from children to adults, men, and women. There is no specific way to predict who will develop these diseases—all age groups, races, and genders are susceptible to inflammatory muscle diseases.

Although, these diseases are commonly found in children ages 5 to 10, and adults ages 40 to 50. Women also have been known to develop inflammatory myopathies twice as often as men.

What are the symptoms of each myopathy?

There are some universal symptoms that myopathies share, such as general muscle weakness, but each type of myopathy is also characterized by its own unique symptoms.

Polymyositis

Dermatomyositis

Dermatomyositis is also sometimes known as ‘polymyositis with a rash’, due to the similarities between these two disorders. The “derma”, or skin aspect of dermatomyositis, differentiates it from other muscular diseases. 

Inclusion Body Myositis

Necrotizing Autoimmune Myopathy

Diagnosis of Myopathies

To diagnose a myopathy, a doctor will consider the patient’s medical history and family medical history and will perform a thorough physical examination, along with various lab tests.

Muscle biopsies may be performed to assess the muscle tissue and measure electrical activity in the muscles, as this can indicate the presence of myopathy.

Blood tests

If your doctor identifies a pattern of muscle weakness in your body, they will likely order a blood test to assess the level of creatine kinase in the blood. Creatine kinase is an enzyme secreted from damaged muscle fibers, so the level of this enzyme will naturally be higher in someone with polymyositis or dermatomyositis specifically, but may appear relatively normal in someone with inclusion body myositis. 

Muscle Biopsy

A muscle biopsy will be one of the first methods for diagnosing an inflammatory myopathy. During this procedure, a small piece of muscle is extracted and examined for damage. This muscle biopsy helps doctors to determine which type of myopathy is present. Muscles affected by polymyositis, for example, will have more of a rounded structure, due to a flood of inflammatory cells in the area.

Treatment of Myopathies

To treat inflammatory muscle diseases, a variety of methods, including immunosuppressive medications, antibody infusions, physical therapy, and healthy lifestyle changes, have proven effective for minimizing some of these inflammatory myopathies. 

Treatment for Polymyositis

Medications are generally the most effective methods for treating degenerative muscle diseases. Drugs that include high doses of corticosteroids (such as prednisone and hydrocortisone) can be very effective at reducing inflammation and managing pain. These medications can help a person to restore lost muscle strength, swallowing ability, respiratory function, and cardiovascular function.

Although, corticosteroids do have the potential of unpleasant side effects, including weight gain, uneven fat distribution, bone loss, and cataracts. For this reason, doctors often prescribe these medications only for a short amount of time.

Antibody infusions are also potential treatment methods for polymyositis. An infusion of antibodies from a healthy donor can slow, or completely stop, the progression of the disease. These antibodies confuse the immune system, causing it to halt its autoimmune attack on the muscles. 

Physical therapy and regular exercise have also proven effective for restoring lost muscle strength and improving range of motion. Fortunately, many people with polymyositis can successfully restore muscle function if the treatment is effective. 

Treatment for Dermatomyositis

The available treatments for dermatomyositis are similar to polymyositis. The main difference is the skin condition associated with this disease. The primary treatment method includes immunosuppressive drugs, like Azathioprine and Methotrexate, to slow the activity of the immune system. 

To prevent exacerbation of the skin condition caused by this disease, it’s advised that people with dermatomyositis avoid direct sunlight, wear sunscreen every day, and wear protective clothing when heading outside.

Topical medications are available to alleviate discomfort associated with the skin condition. Unfortunately, skin conditions have shown to persist for years, despite treatment.

Treatment for Inclusion Body Myositis

Due to the genetic nature of this type of myopathy, treatments for inclusion body myositis are still being studied. Immunosuppressive drugs, such as Azathioprine and Methotrexate, have been tried for years, but have yet to prove effective. 

Your doctor may suggest various drugs to help alleviate the symptoms of inclusion body myositis, but the side effects can be considerable. The best treatment methods currently available for this disease include healthy habits, like physical therapy, exercise, and eating a nutrient-dense diet.  

Treatment for Necrotizing Autoimmune Myopathy

A large percentage of patients diagnosed with necrotizing autoimmune myopathy were found to have been using statins (lipid-lowering medications) or have had a malignant tumor. In this case, the first treatment method would include the cessation of using statins or treatments used to eradicate the malignant tumor. 

Many people with this disease have responded well to long-term therapy with immunosuppressive medications with high-dose corticosteroids. Intravenous immunoglobulin (IVIg) has also proven to effectively minimize this disease. Rituximab, a medication used for autoimmune diseases, has been beneficial in some cases.

The best treatment method for you will depend on a variety of factors, including your specific condition and its severity, any risk factors, your age, your genetic predisposition, and your medical history. The safest and most efficient way to determine the right treatment for you is by visiting your rheumatologist. 

Highly-experienced rheumatologists, like Dr. Maria Farooq, are trained to help patients by identifying and diagnosing the cause of their symptoms and finding appropriate treatments to enhance their quality of life and alleviate any unpleasant symptoms. 

In our UCF Health Rheumatology Services department, we are focused on providing solutions that enable our patients to restore lost function and minimize symptoms. We will work with you to create a personalized treatment plan that addresses your concerns and provides the relief you deserve. 

If you have any questions, please don’t hesitate to reach out to us! Schedule an appointment with a leading rheumatologist in Orlando. 

Sources:

https://rarediseases.info.nih.gov/diseases/13307/necrotizing-autoimmune-myopathy%5C
https://www.mda.org/sites/default/files/publications/Facts_Inflamm_Myopathies_P-199.pdf
https://medlineplus.gov/lab-tests/creatine-kinase/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5476327/
https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Inflammatory-Myopathies-Fact-Sheet#2
https://www.mda.org/sites/default/files/publications/Facts_Inflamm_Myopathies_P-199.pdf
https://www.ninds.nih.gov/disorders/All-Disorders/Inflammatory-Myopathies-Information-Page#:~:text=The%20four%20main%20types%20of,progressive%20muscle%20weakness%20and%20shrinkage
https://medlineplus.gov/ency/article/000821.htm#:~:text=The%20inflammatory%20response%20(inflammation)%20occurs,into%20the%20tissues%2C%20causing%20swelling.
https://www.versusarthritis.org/media/1323/polymyositis-and-dermatomyositis-information-booklet.pdf
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