Description

The inflammatory myopathies are a group of diseases, with no known cause, that involve chronic muscle inflammation accompanied by muscle weakness. The majority of these disorders are considered to be autoimmune disorders, in which the body’s immune response system that normally defends against infection and disease attacks its own muscle fibers, blood vessels, connective tissue, organs, or joints. These rare disorders may affect both adults and children.

The four main types of chronic, or long-term, inflammatory myopathies are:

  • polymyositis, which affects skeletal muscles (involved with making movement)
  • dermatomyositis, which includes a skin rash and progressive muscle weakness
  • inclusion body myositis, which is characterized by progressive muscle weakness and shrinkage
  • necrotizing autoimmune myopathy, with weakness in the uper and lower body, difficulty rising from low chairs or climbing stairs, fatigue, and muscle pain.

General symptoms of chronic inflammatory myopathy include progressive muscle weakness that startes in the proximal muscles--those muscles closest to the trunk of the body.  Other symptoms include fatigue after walking or standing, tripping or falling, and difficulty swallowing or breathing.  Polymyositis and dermatomyositis are more common in women than in men.  Inclusion body myositis is most common after age 50.  Dermatomyositis is more common in children.

Treatment

The chronic inflammatory myopathies can’t be cured in most adults but many of the symptoms can be treated.  Options include medication, physical therapy, and rest.  Polymyositis, dermatomyositis, and necrotizing autoimmune nmyopathy are first treated with high doses of corticosteroid drugs such as prednisone. Immunosuppressant drug may reduce inflammation in individuals who do not respond well to prednisone. Injections of adrenocorticotropic hormone gel may be another option for people who do not respond to or cannot tolerate other drug treatment options. Physical therapy is usually recommended to prevent muscle atrophy as well as to maintain muscle strength and range of motion. Some individuals may use a topical cream to treat skin problems associated with the disorder. IBM has no standard course of treatment. 

Prognosis

Most cases of dermatomyositis respond to therapy. Approximately one-third of individuals with juvenile-onset dermatomyositis recover from their illness, one-third have a relapsing-remitting course of disease, and the other third have a more chronic course of illness. The prognosis for polymyositis varies.  Most individuals respond fairly well to therapy, but some people have a more severe disease that does not respond adequately to therapies and may have significant disability.  IBM is generally resistant to all therapies and its rate of progression appears to be unaffected by currently available treatments.  Necrotizing autoimmune myopathy generally responds well to long-term combination immunosuppressive therapies.  

Research

The National Institue of Neurological Disorders and Stroke (NINDS), along with other agencies within the National Institutes of Health (NIH), conducts and supports a wide range of research on neuromuscular disorders, including myositis and the inflammatory myopathies. The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) is the primary funding institute for these efforts. NIH researchers are working to identify the causes of muscle weakness in order to discover effective treatments.  Researchers are working to develop objective, imaging-based methods for describing the muscle damage associated with inflammatory muscle disease.  NIH-funded researchers are studying childhood-onset polymyositis and dermatomyositis to learn more about their causes, immune system changes throughout the course of the disease, and associated medical problems.  Also, NIH-funded researchers are looking for better, less invasive ways of diagnosing these disorders.  Other NIH-funded researchers are studying the genetic diversity disease susceptibility in the inflammatory myopathies.  Information from the National Library of Medicine’s MedlinePlus Myositis