Types of Myositis

Learn more about the different types of Myositis and Myopathies

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, 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, and Juvenile Myositis.

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Polymyositis (PM)

Polymyositis (PM) is usually diagnosed in people over the age of 20 and affects more women than men. Muscle weakness affects the proximal skeletal muscles, those closest to the bodies core and are used for movement. These muscles usually include the neck, hips, back, and shoulders.  Muscle weakness may happen over days, weeks, or even months.

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Dermatomyositis (DM)

Dermatomyositis (DM) is often diagnosed in people over the age of 20, although the literature states between the ages of 40-60. DM affects more women than men and 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.

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Inclusion Body Myositis (IBM)

IBM is a rare muscle-wasting condition, yet it is the most common degenerative disease of muscle in adults older than 65 years. It is characterized by a slowly progressive, asymmetric, atrophy and weakness of muscles. Patients who have the disease can gradually lose the ability to walk, experience falls and injuries, lose hand function, and have swallowing difficulties.

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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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What are Idiopathic Inflammatory Myopathies?

The Idiopathic Inflammatory Myopathies (IIM) are a heterogeneous group of 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 three main types of chronic, or persistent, inflammatory myopathies are polymyositis, dermatomyositis, and inclusion body myositis.

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. Ocular Myositis frequently manifests with orbital pain and diplopia (double vision).

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Necrotizing Autoimmune Myopathy (NAM)

Necrotizing Autoimmune Myopathy (NAM) is considered to be an extremely rare neuromuscular autoimmune disease. The term “necrosis” is used medically to mean the death of the cells of an organ or tissue due to a disease, injury, or failure of the blood supply.

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Mixed Connective Tissue Disease (MCTD)

Mixed connective tissue disease is classified and considered as an “overlap” of three diseases, systemic lupus erythematosus, scleroderma, and polymyositis. Patients with MCTD typically experience features of each of these three diseases.

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Antisynthetase Syndrome

By definition, the term “syndrome” means a group of signs and symptoms which consistently occur together. It is also referred to as a “constellation” of symptoms.
Antisynthetase Syndrome (ASS) is one such constellation and is included in the acquired inflammatory myopathy category because approximately 90% of people with Antisynthetase Syndrome experience Myositis.

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Toxic Myopathy

Myositis can be triggered by a variety of reasons, some known and some unknown. Toxic Myopathy (also known as Toxic Myositis) is diagnosed when Myositis is thought to be triggered by drugs and chemicals. And, according to Johns Hopkins, cholesterol lowering medications, particularly the “statins”, may be the most commonly prescribed drugs that can cause a toxic myopathy. 

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Infectious/Viral Myositis

Myositis can occur after suffering a viral, bacterial, fungal, or parasitic infection, and the effects of the disease can range from mild muscle pain (myalgia) to the severest form, rhabdomyolysis in which renal failure can occur. Infectious Myositis mimics the symptoms of Polymyositis, typically impacting proximal muscles; those muscles which are close to the body’s core.

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