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What is Myositis (including Polymyositis and Dermatomyositis)?

Myositis is a group of rare diseases defined by inflamed muscles, which can cause prolonged muscle weakness, pain, and fatigue. There are 4 types of myositis. Polymyositis and dermatomyositis are the two common types of myositis. Polymyositis causes muscle weakness, typically in the muscles nearest to the trunk of the body. Dermatomyositis causes muscle weakness, as well as a skin rash. The other two types of myositis are inclusion body myositis and juvenile myositis. These conditions, sometimes referred to as inflammatory myopathies, can affect the skin, internal organs, and multiple muscle groups of patients. Myositis can affect people of all ages, including children.

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Causes of Myositis (including Polymyositis and Dermatomyositis)

The exact cause of myositis is not known. Myositis is believed to be an autoimmune disease in which the body’s immune system attacks its own skeletal muscles causing inflammation and progressive weakening of these muscles. Most cases do not have a known cause. However, it is believed that infection and injury may play a role.

Some experts believe that myositis may also be caused by:

  • Drug toxicity
  • Viruses such as the flu, common cold, and HIV
  • Autoimmune conditions such as lupus and rheumatoid arthritis

Symptoms of Myositis (including Polymyositis and Dermatomyositis)

While each myositis condition has its own distinctive characteristics and treatments, all of them involve chronic muscle inflammation. This inflammation typically results in muscle fatigue and weakness, swelling of the feet and legs, frequent falling, and joint and muscular pain.

Early symptoms in people with myositis, including polymyositis and dermatomyositis, include:

  • Trouble standing up from a seated position
  • Trouble climbing stairs
  • Trouble lifting the arms
  • Fatigue after walking or standing for a long time
  • Difficulty swallowing or breathing
  • Hoarseness in the voice
  • Pain in the muscles that do not abate in a few weeks
  • A purple or red-colored rash on body parts, such as elbows, knuckles, knees, and eyelids

Diagnosis of Myositis (including Polymyositis and Dermatomyositis)

Individuals with myositis are often given a misdiagnosis. It can be difficult to diagnose myositis since it is a rare condition, and also because the chief symptoms are muscle weakness and fatigue, which can be found in several other common conditions.

Doctors may use any of the following tests to assist in the diagnosis:

  • Physical examination
  • Biopsy of the muscle
  • Blood tests to ascertain creatine phosphokinase (CPK) levels
  • Magnetic resonance imaging (MRI)
  • Electromyography
  • Genetic testing
  • Nerve conduction study
  • Antinuclear antibody (ANA) blood test
  • Myositis specific antibody panel blood test

Treatment of Myositis (including Polymyositis and Dermatomyositis)

There is no cure for the disease. Treatment only slows the progression of the disease and is aimed at reducing pain and inflammation. Treatment recommendations include rest, exercise, non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids, and immune-suppressants.

In general, the treatment for myositis varies according to the cause. Inflammatory conditions causing myositis may necessitate treatment with drugs that suppress the immune system and help reduce swelling. These drugs are known as disease-modifying anti-rheumatic drugs (DMARD) and include:

  • Azathioprine (Imuran)
  • Prednisone
  • Methotrexate

Myositis caused by infection is normally due to a virus, and no specific treatment is required. Myositis caused by bacteria is rare and typically necessitates antibiotics to avert the life-threatening spread of the infection.

Corticosteroids are the main type of medication employed to treat dermatomyositis and polymyositis. They aid in the quick reduction of swelling and ease muscle pain.

Myositis connected to a specific drug is treated by discontinuing the medication. In cases of myositis caused by statin drugs, muscle inflammation normally subsides within a couple of weeks after discontinuing the medication.

Biologic therapies, such as rituximab, can also assist in managing the symptoms of myositis. They are extensively utilized to treat diseases such as psoriatic arthritis and rheumatoid arthritis. They help to decrease swelling and tend to be only utilized for severe myositis.

Physical therapy, exercise, yoga, and stretching may also be involved as a treatment to help keep muscles flexible and strong and prevent muscle atrophy.

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