Myositis

Myositis is a rare disease that involves inflammation of the muscles.[2] It can present with a variety of symptoms such as skin involvement (i.e., rashes), muscle weakness, and other organ involvement.[3] Systemic symptoms such as weight loss, fatigue, and low fever can also present.

For the "forget-me-nots" plant genus, see Myosotis. For the phase of cell division where replicated chromosomes are separated into two new nuclei, see Mitosis. For the genus of bats otherwise known as “mouse-eared bats”, see Myotis.
Myositis
A muscle biopsy from someone who is diagnosed with myositis.
SpecialtyRheumatology
ComplicationsAmplified musculoskeletal pain syndrome[1]
CausesAutoimmunity, idiopathic, adverse drug reaction

Causes

Injury, medicines, infection, inherited muscle disease, or an autoimmune disorder can lead to myositis. It can also be idiopathic (no known cause).

  • Injury - A mild form of myositis can occur with hard exercise.[4] A more severe form of muscle injury, called rhabdomyolysis, is also associated with myositis.[4] This is a condition where injury to the patient's muscles causes them to quickly break down.[4]
  • Medicines - A variety of different medicines can cause myositis. One of the most common drug types that can cause myositis is statins. Statins are drugs that are used to help lower high cholesterol. One of the most common side effects of statin therapy is muscle pain.[5] Rarely, statin therapy can lead to myositis.[5]
  • Infection - The most common infectious cause of myositis is viral infections, such as the common cold.[4] It can also include bacterial, parasitic, and fungal infections.[6] Viruses, such as COVID-19, are also shown to be a rare cause of myositis.[7] Benign acute childhood myositis has been described in children after prodromal viral infections with different viral agents.
  • Inherited muscle disease - Many inherited myopathies may have secondary myositis, including calpainopathy, dysferlinopathy, fascioscapulohumeral muscular dystrophy, dystrophinopathy, and LMNA-associated myopathy.[8]
  • Autoimmune - Autoimmune disease is an abnormal immune response to a functioning body part, in this case the muscles. The three main types of idiopathic myositis (known as inflammatory myopathies) that typically test positive for autoantibodies are dermatomyositis, polymyositis, and inclusion body myositis.[4] Other autoimmune diseases, such as systemic lupus erythematosus, can also cause myositis-like symptoms.[4]

Diagnosis

There are various tools that can be used to help diagnose myositis. The most common ones are physical exam, electromyography, magnetic resonance imaging, muscle biopsy, and blood tests. The first thing a doctor will likely do is perform a physical exam.[2] The doctor looks for various things such as muscle weakness and rashes.

Another possible test is an electromyography (EMG). This is a test that inserts tiny needles into the patient's muscles.[4] This allows a physician to look at the muscles’ response to various electrical nerve signals and evaluate which muscles potentially have myositis.[4] Magnetic resonance imaging (MRI) is also useful.[9] This test uses a big magnet to create images of muscles on a computer.[4] It is painless.

Muscle biopsies are the most reliable tests for diagnosing myositis.[4]

There are also a variety of blood tests available that help in the diagnoses of myositis. The doctor may look for elevation of creatine kinase in blood, which is indicative of muscle inflammation.[4] Certain autoantibodies (antibodies that target muscle cells) can also be found in the blood, which can indicate that myositis is caused by an autoimmune disease.[3] Some specific examples of autoantibodies are Anti-Jo-1, Anti-HMGCR, Anti-TIF1, etc.[3]

Treatment

Treatment for myositis depends on the underlying cause.[4] For myositis that is caused by a viral infection, no treatment is typically needed.[4] For myositis caused by a bacterial infection, antibiotics can be used.[4] For myositis caused by a medication, it is important to stop use of that medication.[4]

There are a variety of treatment options available if myositis is caused by an autoimmune disease. Glucocorticoids are often the first choice for treatment.[10] This drug works to weaken the immune system, so that the immune system is not able to attack the muscles. It is a type of steroid and can cause a wide array of side effects such as mood changes, increased hunger, trouble sleeping, etc. Another treatment option is a steroid-sparing immunosuppressive agent.[10] This also works to weaken the immune system, but does not cause the side effects that the steroids do. Another treatment option is a class of drugs called biologics.[10] Also, intravenous immunoglobulins (IVIg) have also been shown to be effective in the treatment of myositis caused by an autoimmune disease.[11]

See also

References
  1. "Amplified Musculoskeletal Pain Syndrome (AMPS)". Children's Health.
  2. Carstens PO, Schmidt J (March 2014). "Diagnosis, pathogenesis and treatment of myositis: recent advances". Clinical and Experimental Immunology. 175 (3): 349–358. doi:10.1111/cei.12194. PMC 3927896. PMID 23981102.
  3. Betteridge Z, McHugh N (July 2016). "Myositis-specific autoantibodies: an important tool to support diagnosis of myositis". Journal of Internal Medicine. 280 (1): 8–23. doi:10.1111/joim.12451. PMID 26602539. S2CID 41157692.
  4. Hoffman M (19 April 2021). DerSarkissian C (ed.). "Myositis: Symptoms and Causes". WebMD. Retrieved 2022-06-12.
  5. Sathasivam S, Lecky B (November 2008). "Statin induced myopathy". BMJ. 337: a2286. doi:10.1136/bmj.a2286. PMID 18988647. S2CID 3239804.
  6. Szczęsny P, Świerkocka K, Olesińska M (2018). "Differential diagnosis of idiopathic inflammatory myopathies in adults - the first step when approaching a patient with muscle weakness". Reumatologia. 56 (5): 307–315. doi:10.5114/reum.2018.79502. PMC 6263305. PMID 30505013.
  7. Saud A, Naveen R, Aggarwal R, Gupta L (July 2021). "COVID-19 and Myositis: What We Know So Far". Current Rheumatology Reports. 23 (8): 63. doi:10.1007/s11926-021-01023-9. PMC 8254439. PMID 34216297.
  8. Tarnopolsky MA, Hatcher E, Shupak R (May 2016). "Genetic Myopathies Initially Diagnosed and Treated as Inflammatory Myopathy". The Canadian Journal of Neurological Sciences. Le Journal Canadien des Sciences Neurologiques. 43 (3): 381–384. doi:10.1017/cjn.2015.386. PMID 26911292. S2CID 25515951.
  9. Pipitone N (November 2016). "Value of MRI in diagnostics and evaluation of myositis". Current Opinion in Rheumatology. 28 (6): 625–630. doi:10.1097/BOR.0000000000000326. PMID 27454210. S2CID 25027014.
  10. Sasaki H, Kohsaka H (November 2018). "Current diagnosis and treatment of polymyositis and dermatomyositis". Modern Rheumatology. 28 (6): 913–921. doi:10.1080/14397595.2018.1467257. PMID 29669460. S2CID 4934267.
  11. Mulhearn B, Bruce IN (March 2015). "Indications for IVIG in rheumatic diseases". Rheumatology. 54 (3): 383–391. doi:10.1093/rheumatology/keu429. PMC 4334686. PMID 25406359.

Myositis Association https://www.myositis.org

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