Myositis
Myositis is a term used to describe a group of rare chronic conditions characterized by inflammation of the skeletal muscles, leading to muscle weakness. This condition encompasses several forms, including polymyositis, dermatomyositis, inclusion-body myositis, and juvenile myositis, all of which are believed to be autoimmune diseases. Though the exact cause of myositis remains unclear, it is thought that environmental triggers, such as viral infections, may activate the condition in genetically predisposed individuals. The immune system mistakenly attacks the muscle tissue, resulting in various symptoms like fatigue, difficulty with physical activities, and, in some cases, skin issues.
Diagnosis of myositis can be complex, as symptoms may mimic other diseases, requiring a combination of physical exams, imaging tests, blood tests, and muscle biopsies for confirmation. Treatment typically focuses on reducing inflammation through rest, physical therapy, and medications such as corticosteroids and other immunosuppressants. While there is no known prevention for myositis, managing sun exposure can help reduce the severity of symptoms in those with dermatomyositis. Understanding myositis is essential for those experiencing its symptoms or seeking to support individuals affected by these challenging conditions.
Myositis
- ANATOMY OR SYSTEM AFFECTED: Muscles, musculoskeletal system
- ALSO KNOWN AS: Idiopathic inflammatory myopathy, inflammatory myopathy
Definition
Myositis is a general term for a group of rare chronic conditions characterized by inflammation of the skeletal muscles. This inflammation can cause muscle weakness. Myositis refers to the inflammatory myopathies, including polymyositis, dermatomyositis, inclusion-body myositis, and juvenile myositis. It is thought that all these disorders are autoimmune diseases. Inflammatory myopathies can also be caused by certain medications or by exposure to a toxic substance; these myopathies are usually not chronic and resolve once the harmful substance is removed.
Causes
It is not known what causes myositis. It is believed that an environmental factor, such as a viral infection, triggers myositis in people who might be genetically predisposed to the condition. The damage in myositis is caused by the body’s own immune system, as white blood cells and antibodies attack the muscle and, in some cases, the skin.
Risk Factors
Generally, women are affected more often than men, although inclusion-body myositis affects twice as many men as women. Polymyositis is observed in persons between twenty and sixty years of age, whereas inclusion-body myositis is more common after age fifty years. Children can develop dermatomyositis. African Americans are at higher risk for myositis, while the lowest rates of myositis are reported in persons of Japanese origin.
Symptoms
Common symptoms of the inflammatory myopathies include muscle weakness, sometimes with muscle pain, that lasts for more than a few weeks; general tiredness and fatigue; difficulty climbing stairs, standing up from a seated position, or reaching up; and difficulty swallowing. Additional symptoms for the various myopathies include a variety of skin symptoms (such as a rash or scaly, dry, and rough skin) in dermatomyositis; and hardened lumps of calcium (calcinosis) under the skin in juvenile dermatomyositis. Unlike other inflammatory myopathies, the muscle weakness in inclusion-body myositis is often asymmetrical.
Screening and Diagnosis
Myositis varies from person to person and can often resemble other diseases, such as scleroderma or systemic lupus erythematosus (SLE, or lupus). Tests used to help confirm a diagnosis include a physical exam; tests of muscle strength; magnetic resonance imaging (MRI) scan; an electromyogram (EMG); blood tests, including erythrocyte sedimentation rate, creatinine kinase, and antinuclear antibodies; and muscle and skin biopsies. A muscle biopsy is the most accurate test for diagnosing myositis.
Treatment and Therapy
Treatment for myositis generally includes rest, physical therapy, and the use of anti-inflammatories (corticosteroids as first-line therapy and methotrexate, hydroxychloroquine, and azathioprine), and intravenous immunoglobulin. If left untreated, inflammatory myopathy can cause permanent damage.
Prevention and Outcomes
Because the cause of myositis is unknown, there is no known way to prevent the condition. To lessen the severity of dermatomyositis, however, persons with the condition should avoid excessive exposure to the sun, which can worsen any dermatomyositis-associated skin rashes.
Bibliography
Hoffman, Matthew. “Myositis.” WebMD, 1 May 2023, www.webmd.com/a-to-z-guides/myositis-symptoms-treatments-prognosis. Accessed 22 Oct. 2024.
Isenberg, D. A., et al. “International Consensus Outcome Measures for Patients with Idiopathic Inflammatory Myopathies: Development and Initial Validation of Myositis Activity and Damage Indices in Patients with Adult Onset Disease.” Rheumatology, vol. 43, no. 1, Jan. 2004, pp. 49-54.
Kagen, Lawrence J., editor. The Inflammatory Myopathies. Humana Press, 2009.
Marieb, Elaine N. Essentials of Human Anatomy and Physiology. 8th ed., Pearson/Benjamin Cummings, 2006.
Murphy, Kenneth, et al. Janeway’s Immunobiology. 7th ed., Garland Science, 2008.
Parker, James N., and Philip M. Parker, editors. Myositis: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. ICON Health, 2004.