Myositis: The Basics

Simply Put

The primary focus of Myositis Support and Understanding is muscle diseases which are referred to as “Idiopathic Inflammatory Myopathies” or “Acquired Myopathies,” meaning muscle diseases which are typically not inherited and are caused by the immune system attacking muscles, connective tissue, blood vessels, and/or the skin. Idiopathic means the cause is unknown.

Polymyositis causes muscle weakness around the middle of the body and affects both sides of the body. Dermatomyositis causes muscle weakness as well as skin rashes. Juvenile dermatomyositis differs from the adult form because of the coexistence of vasculitis (inflammation of blood vessels). Inclusion body myositis mainly affects older individuals. As muscle weakness becomes severe, it is accompanied by muscle wasting and diminished deep-tendon reflexes. Unlike polymyositis and dermatomyositis, the muscle weakness is often not symmetric and may be prominent in the smaller muscles of the forearms and calves.

LIftseat for Myositis

The most common types of these rare diseases are:

  • Polymyositis (PM)
  • Dermatomyositis (DM)
  • Inclusion Body Myositis (IBM)
  • Juvenile Myositis: Juvenile Dermatomyositis (JDM) and Juvenile Polymyositis (JPM)

There are even more rare Myositis subcategories which include:

  • Toxic Myositis
  • Necrotizing Autoimmune Myopathy
  • Orbital or Ocular Myositis (OM)
  • Infectious or Viral Myositis

Syndromes, diseases which consist of multiple disorders and include Myositis:

  • Antisynthetase Syndrome (ASS)
  • Mixed Connective Tissue Disease (MCTD)

What Does Myositis mean?

The prefix ”Myo” means muscle. The term “Myopathy” indicates any disease, inflammation, or weakness of the muscle, whereas “Myositis” is a specific group of muscle diseases, most often those which are both idiopathic (no known cause) and autoimmune in nature.   However, the terms “Myositis” and “Myopathy” are occasionally used interchangeably and some, very rare types of Myositis can be traced to genetic inheritance.

We have found through experiences shared in our Facebook Support Groups that some people are being diagnosed with “Myalgia and Myositis,” which actually is not a disease diagnosis but rather symptoms. The terms simply mean that they are experiencing muscle weakness and pain, which can be indications of many diseases. This is not the “Myositis” we discuss as an Idiopathic Inflammatory Myopathy.

How Does Myositis Affect People?

Myositis is a chronic, progressive, inflammatory disease which most often is indicated by muscle weakness and skin rashes. Other symptoms may include pain, fatigue, trouble swallowing, shortness of breath, lung disease, fevers, and weight loss. Patients often have difficulty climbing stairs, rising from a seated position, turning over in bed, raising their arms over their head, and grasping items with their hands, and many become prone to falls. Symptoms can appear gradually, over a period of months or even years, or it may develop more rapidly, within days or weeks.

Depending upon the amount of muscle weakness and extent of muscle wasting, some patients may require the use of a cane, walker, wheelchair, power chair, or other assistive devices. Some may also require the use of toilet lifts such as LiftSeat. Early detection and prompt treatment will provide patients with the best possible chance of remission.

What Causes Myositis?

While there are some known causes of Myositis such as medications, toxins, infections, electrolyte level imbalance, trauma, and thyroid and inherited diseases, many doctors and researchers believe the majority of Myositis cases are caused by a misguided immune system response. The immune system normally fights infections, but for often unknown reasons in autoimmune diseases, the immune system wages an attack on the body’s own normal, healthy tissues.

Does Myositis cause pain?

The short answer is yes, Myositis may cause pain. According to the latest statistics, about 40% of U.S. Myositis patients will experience pain.

Doctors were taught in medical school for many years that pain was not a part of Myositis. So, some of the older doctor may still believe this.  The doctors that truly know Myositis, however will tell you that pain can be a part of Myositis and can be debilitating.

Is Myositis a Rare Disease?

Myositis and its subtypes are rare diseases according to National Organization for Rare Disorders (NORD). It is currently estimated that 5-10 people per million are diagnosed with a type of Myositis each year. In the U.S., that equates to only 1,600 to 3,200 cases per year. The exact number of Myositis cases is difficult to measure, but according to the latest estimate, is was thought, with all forms combined, that there are 50,000 to 75,000 people living with Myositis in the U.S.

Who Gets Myositis?

Although Myositis can affect people of any age, most children who get the disease are between 5 and 15 years of age and most adults are between 30 and 60 years of age. Like many autoimmune diseases, most types of Myositis affect more women than men with the exception being Inclusion Body Myositis, which affects more men than women.

How is Myositis Diagnosed?

Diagnosing Myositis may be a lengthy and challenging process because many of the symptoms resemble other, more common diseases. Additionally, since most medical professionals lack experience with Myositis, it is not uncommon for patients to be misdiagnosed, which may require seeing multiple physicians prior to receiving an accurate diagnosis and treatment program.

There are a variety of comprehensive tests which are frequently used in a “differential diagnosis,” which helps eliminate other possible diseases and pinpoint a more accurate diagnosis including:

  • Electromyography (EMG)
  • Magnetic Resonance Imaging (MRI)
  • Nerve Conduction Study (NCS)
  • Blood tests to determine CK (CPK) levels
  • Antinuclear Antibody (ANA) blood test
  • Myositis Specific Antibody panel (MSA) blood test
  • Biopsies of the affected muscle and/or skin tissue
  • For difficult cases, genetic testing may be ordered

Many physicians experienced with Myositis believe that the biopsy, although an invasive procedure, is the most reliable test to confirm the presence of Myositis and determine the type.

Did you know it has been noted that more muscle biopsies are performed to diagnose inflammatory myopathies than for any other category of muscle disease?

Can Myositis be Cured or Treated?

There is currently no known cure for any form of Myositis however, with proper, expeditious treatment, some patients may experience partial or complete remission while others may experience active or progressive disease of some or all symptoms for their entire lives.

What Types of Treatments Are Effective for Myositis?

While no medications have been developed specifically to treat Myositis, several medications and therapies used in other autoimmune and inflammatory diseases have been shown to be effective in treating the symptoms in many patients. For the types of Myositis which respond to treatment, corticosteroids, such as Prednisone, is typically the initial treatment followed by immune suppressing agents. It is not uncommon to try multiple medications, sometimes in combination with infusions, to find the right treatment for each individual.

Myositis affects each patient differently often making treatment a trial-and-error process. Finding the right medication or combination of medications is important to help slow the autoimmune process. If left untreated Myositis can cause significant morbidity and even death.

Exercise is an important part of treating myositis. It was once thought that exercise would cause more damage to the muscles but this has since been proven false. Talk to your doctor about starting an exercise program.

There are also refractory cases in which patients do not respond to the typical medications used in treating Myositis.

Myositis, in photos

inflammatory myopathies
Myositis Biopsies
DM muscle biopsy

Simply Put

“Simply Put” is a service of Myositis Support and Understanding, to provide overviews of Myositis-related medical and scientific information in understandable language.

MSU volunteers, who have no medical background, read and analyze often-complicated medical information and present it in more simplified terms so that readers have a starting point for further investigation and consultation with healthcare providers. The information provided is not meant to be medical advice of any type.

The above information is provided as a basic overview of a complicated group of diseases. For more in-depth information, you are encouraged to explore the individual topics covered in the MSU website.

© Myositis Support and Understanding Association, Inc. 2010-2017. All Rights Reserved. MSU is a 501(c)(3) nonprofit organization.

You agree to our Terms and Conditions and Privacy Policy by using and viewing our site.

Want to make a tax-deductible donation? Visit our Donate page today!


Log in with your credentials


Forgot your details?


Become a Member

Send this to a friend