Idiopathic Inflammatory Myopathy, also known as myositis, is a group of conditions characterised by chronic inflammation of skeletal muscle tissues involved in movement, resulting in muscle weakness.^1,2  These conditions can also affect other organs such as skin, joints, lungs, heart and gastrointestinal tract, and are typically progressive.¹ Whilst the underlying cause of these conditions is generally not fully understood, they often have an autoimmune component, in which the body’s immune system produces antibodies attacking itself.

Myositis can affect both adults and children depending on the specific condition. Different forms of myositis include:^1-3

• Polymyositis (PM)
• Inclusion body myositis (IBM)
• Dermatomyositis (DM)
• Juvenile myositis
• Necrotizing autoimmune myopathy (NAM) also known as immune-mediated necrotizing myopathy (IMNM)

Myositis is also a feature of various other conditions such as overlap myositis (OM), antisynthetase syndrome, eosinophilic fasciitis and necrotizing myositis/fasciitis. As a relatively less well-known group of diseases, myositis has been said to be, at times, misdiagnosed as other conditions that share similar symptoms, including motor neuron disease (MND).

Synonyms: idiopathic inflammatory myopathy, Familial; idiopathic inflammatory myositis.

Universal rare disease classifications provide a common language for recording, reporting and monitoring diseases. Please visit the Rare Disease Classifications page for more information about these internationally recognised classifications.

ORPHA:98482 Idiopathic inflammatory myopathy

ICD-11: 4A41 Idiopathic inflammatory myopathy

Common symptoms of myositis include muscle weakness, low muscle strength and muscle pain (myalgia). Other symptoms vary between the different types of myositis and may affect other organs such as skin, joints, lungs, heart and gastrointestinal tract.¹

Please speak to your medical team to learn more about the symptoms and complications for a specific type of myositis.

Rare diseases are often serious and progressive, exhibiting a high degree of symptom complexity, leading to significant disability. Majority of the estimated two million Australians living with a rare disease meet the Australian Government’s definition for disability (in accordance to the Australian Public Service Commission and Australian Bureau of Statistics), and many experience severe and permanent disability impacts. If you or someone you care for is experiencing disability-related impacts from a rare condition, please speak with a health or disability professional for advice. Information about relevant disability support can be found at the RARE Portal’s Disability Support Information page.

The underlying cause of most, if not all, myositis conditions is not fully understood. Myositis conditions are generally classified as autoimmune disorders (in which the body’s immune system produces antibodies attacking itself) and are not inherited.

A large proportion of individuals with myositis have myositis-specific autoantibodies (MSA) or myositis-associated autoantibodies (MAA), which are autoantibodies also associated with other autoimmune disorders.¹ There are also some individuals with myositis that do not have any known autoantibodies (seronegative IIM)

Diagnosis of myositis will depend on the specific type of myositis and may include some or all of the following:^1,3

• a muscle biopsy
• a skin biopsy (for those with symptoms relating to skin)
• blood tests to check for elevated creatine kinase (CK) levels and/or auto-antibodies
• electromyography (EMG) to assess nerve-to-muscle signal transmission; to identify it is a muscle-related disorder
• muscle imaging with magnetic resonance imaging (MRI) or computed tomography (CT) scans to detect for disease-specific patterns

Differential diagnostic tests may also be performed to rule out other conditions that share similar symptoms.

Please speak to your medical team to learn more about the available diagnostic pathways for a specific type of myositis.

There is currently no curative treatment for myositis. Treatment is targeted at restoring muscle strength, reducing or eliminating inflammation and preventing further organ damage.³

Please speak to your medical team to learn more about the possible treatment or management options for your condition. Treatment will depend on an individual’s specific condition and symptoms. It is also important to stay connected to your medical team so that you can be made aware of any upcoming clinical trial opportunities.

Clinical care for rare diseases often involves a multidisciplinary team of medical, care and support professionals. Please note that the information provided here is as a guide and that RVA does not necessarily monitor or endorse specific clinics or health experts.

Healthcare professionals involved in the treatment of Myositis may include general practitioners (GP), rheumatologists, dermatologists, neurologists, physiotherapists and occupational therapists. The need for different healthcare professionals may change over a person’s lifetime and extend beyond those listed here.

Myositis Association Australia provides its members with a list of medical and allied health professionals who have experience in advising people living with Myositis.

There may be specific clinical care guidelines for the individual myositis conditions.

Information for specific myositis conditions will be added in time.

Individuals living with rare diseases may have complex medical issues and disabilities, which are not always visible. It is often useful to refer to their medical history as well as personal information such as a medical card, doctor’s letter, or if available, a rare disease passport, for relevant information.

For research updates, please visit the Myositis Association Australia: Current Research.

There are specific considerations around participating in rare disease research, including clinical trials. It is important to be mindful of issues such as data privacy, research ethics, consent and differences in research regulations between Australia and other countries.

If you are interested in finding clinical trials for your condition, please visit the following websites; however, there may not be any clinical trials available:

• Australian Clinical Trials
• ClinicalTrials.gov

It is best to discuss your interest in any clinical trials with your medical team to determine suitability and eligibility.

Please note that RVA does not necessarily monitor or endorse each group/organisation’s operational governance and activities.

Australian Organisation:

Myositis Association Australia
Website: https://myositis.org.au/

The Myositis Association – Australia Inc is a registered charity, run by volunteers, who have Myositis.They provide support and advocacy for individuals living with Myositis, their carers, family members and friends. Their goal is to help more people keep in touch, share their experiences and learn practical ways to manage their condition. They also work to raise awareness of Myositis and to support Australian-based research looking into ways to prevent and treat the disease as well as improving the quality of life for those living with Myositis.

Please note that RVA does not monitor or endorse each group/organisation’s operational governance and activities. When engaging with a group, please consider the information on the RARE Portal’s Finding Helpful Peer and Community Supports page.

Myositis varies between individuals, and each person’s experience is unique.

Please visit Myositis Association Australia: Myo Journeys to read the personal stories of people living with Myositis.

Personal stories shared with Rare Voices Australia:

• Lachy’s Story
• Damian’s Story
• Tracy’s Story
• Natasha’s Story

If you would like to share your personal story with RVA, please visit the Rare Voices Australia: Share Your Story page. RVA will consider your story for publishing on our website and inclusion on the RARE Portal.

For information on available government and social services that provide support for individuals with a rare disease, please visit the National and State Services pages.

People living with a rare disease, including families and carers, often face unique challenges such as diagnostic delays, misdiagnoses, limited treatment options, and limited access to rare disease specialists and support. These challenges may impact people’s emotional wellbeing and quality of life. Many people find it helpful to seek mental health and wellbeing support to cope with ongoing stress and uncertainty. Connecting with people who have shared experiences through a support group may also be helpful. Information about relevant mental health and wellbeing support can be found at:

• Mental Health and Wellbeing Support for Australians Living with a Rare Disease
• The National and State Services pages underneath the ‘Mental Health’ sections listed

Information on the different types of Myositis can be found at:

• The Loop – Your Neuromuscular Resource Hub: Idiopathic Inflammatory Myopathies (IIM)
• The Loop – Your Neuromuscular Resource Hub: Inclusion Body Myositis (IBM)

• Myositis Association Australia – Information for Health Professionals
• Orphanet: Idiopathic Inflammatory Myopathy

This page has been co-developed by Rare Voices Australia (RVA)’s RARE Portal team in consultation with Myositis Association Australia.

If you are aware of any additional information that may benefit stakeholders with an interest in this page, or if you notice any broken links or inaccurate information, please let us know via the Contribute page.