Idiopathic Inflammatory Myopathies (IIM)

Referred to as myositis

Myositis, like many autoimmune diseases,  is a complex illness that is often misunderstood.  Each patient presents differently, making the diagnostic process that much harder. Learn more about the different types of Myositis.

Myositis: The Basics

The primary focus of Myositis Support and Understanding is rare 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, lungs, and/or the skin.

Although we do provide information about other forms of Myositis, the ones we focus on are Polymyositis, Dermatomyositis, Inclusion Body Myositis, Immune-Mediated Necrotizing Myopathy, Antisynthetase Syndrome, and Juvenile Myositis.

All forms of Idiopathic Inflammatory Myopathies are rare diseases.

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Polymyositis (PM)

Polymyositis (PM) presents with muscle weakness affecting the proximal skeletal muscles, those closest to the bodies core and used for movement. These muscles can include the neck, hips, back, and shoulders. Muscle weakness may happen over days, weeks, or months. Myositis antibodies can aid in a diagnosis, and in some cases, may aid in predicting disease course and potential treatment outcomes. Lung disease and, to a lesser extent, cancer, may accompany PM.

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Dermatomyositis (DM)

Dermatomyositis (DM) has recently been found to be more prevalent in African-American women, although this is poorly understood. Like with PM, muscle weakness affects the proximal skeletal muscles and also presents with skin rashes and other skin-related markers that may make diagnosis easier. Myositis antibodies can aid in a diagnosis, and in some cases, help predict disease course and potential treatment outcomes. Lung disease and cancer can accompany DM.

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Antisytnetase Syndrome (AS)

Antisynthetase syndrome is associated with a number of known autoantibodies called aminoacyl-tRNA synthase (ARS) autoantibodies. AS includes Interstitial lung disease (ILD), Polymyositis (PM) or Dermatomyositis (DM), Polyarthritis (inflammation of many joints), Raynaud’s Phenomenon, and Mechanic’s Hands. Not all of these are present in AS patients. For some, the lungs may be the primary organ affected.

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Inclusion Body Myositis (IBM)

IBM is a rare muscle-wasting condition, yet it is the most common myopathy in those over age 50. It is characterized by slowly progressive, asymmetric, muscle atrophy and weakness. Patients who have the disease gradually lose the ability to walk, experience falls and injuries, lose hand function and have swallowing difficulties (dysphagia) with the risk of choking and aspiration pneumonia.

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What are Idiopathic Inflammatory Myopathies?

The Idiopathic Inflammatory Myopathies (IIM) are a heterogeneous group of rare muscle diseases of unknown etiology characterized by inflammation of the muscles used for movement; the skeletal muscles.

Myopathy is a term used to describe muscle disease.  The inflammatory myopathies are a group of diseases that involve chronic muscle inflammation, accompanied by muscle weakness.  Another word for chronic inflammation of muscle tissue is myositis.

The four main types of adult, chronic idiopathic inflammatory myopathies are polymyositis, dermatomyositis, immune-mediated necrotizing myopathy, antisyntetase syndrome, and inclusion body myositis.

Juvenile Myositis (JM)

Juvenile Myositis (JM), including Juvenile Dermatomyositis (JDM) and Juvenile Polymyositis (JPM), are rare autoimmune conditions which cause inflammation. The inflammation for JPM primarily occurs in the muscles, while in JDM the inflammation is in the blood vessels that lie under the skin and in the muscle tissue. This inflammation causes weak muscles and – in the case of JDM – skin rashes.

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Immune-Mediated Necrotizing Myopathy (IMNM)

Immune-Mediated Necrotizing Myopathy (IMNM) is a rare autoimmune disease with symptoms similar to polymyositis. The muscle biopsy is what really distinguishes the two. IMNM can be associated with statin use but not always. Myositis antibodies are helpful for a diagnosis for IMNM. CPK levels with IMNM are extremely high.

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Orbital/Ocular Myositis (OM)

Orbital or Ocular Myositis (OM) is an extremely rare autoimmune disorder which affects the extraocular muscles of the eye, which are muscles that control eye movement. Orbital Myositis frequently manifests with orbital pain and diplopia (double vision). Usually OM impacts young to middle-aged adult women. Treatment is often successful but there is no cure.

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