View source for Myositis

{{short description|Inflammation of skeletal muscle}}
{{for multi|the "forget-me-nots" plant genus|Myosotis|the phase of cell division where replicated chromosomes are separated into two new nuclei|Mitosis|the genus of bats otherwise known as "mouse-eared bats"|Myotis}}
{{Infobox medical condition (new)
| name            = Myositis
| synonyms        =

| image           = IBM rimmed vacuoles HE x200.jpg
| caption         = A muscle biopsy from someone who is diagnosed with{{clarify|date=July 2024}}{{explain|date=July 2024|reason=what in the picture shows that, what is what?}} myositis.
| pronounce       =
| field           = [[Rheumatology]]
| symptoms        =
| complications   = [[Amplified musculoskeletal pain syndrome]]<ref name=ChildrensHealth>{{cite web |url=https://www.childrens.com/specialties-services/conditions/amplified-musculoskeletal-pain-syndrome-amps |title=Amplified Musculoskeletal Pain Syndrome (AMPS) |publisher=Children's Health}}</ref>
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| causes          = [[Autoimmunity]], [[idiopathic]], [[adverse drug reaction]]
| risks           =
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| differential    =
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'''Myositis''' is a rarely-encountered [[Disease|medical condition]] characterized by [[inflammation]] affecting the [[Skeletal muscle|muscles]].<ref name="Carstens_2014">{{cite journal |vauthors=Carstens PO, Schmidt J |date=March 2014 |title=Diagnosis, pathogenesis and treatment of myositis: recent advances |journal=Clinical and Experimental Immunology |volume=175 |issue=3 |pages=349–358 |doi=10.1111/cei.12194 |pmc=3927896 |pmid=23981102}}</ref> The manifestations of this condition may include [[Human skin|skin]] issues, [[muscle weakness]], and the potential involvement of other organs.<ref name="Betteridge_2016">{{cite journal |vauthors=Betteridge Z, McHugh N |date=July 2016 |title=Myositis-specific autoantibodies: an important tool to support diagnosis of myositis |journal=Journal of Internal Medicine |volume=280 |issue=1 |pages=8–23 |doi=10.1111/joim.12451 |pmid=26602539 |s2cid=41157692 |doi-access=free}}</ref> Additionally, [[systemic symptom]]s like weight loss, [[fatigue]], and [[low-grade fever]] can manifest in individuals with myositis.

==Causes==
Myositis can arise from various causes, including [[injury]], certain [[medication]]s, [[infection]]s, inherited muscle disorders, or [[Autoimmune disease|autoimmune conditions]]. In some instances, the origins of myositis remain [[Idiopathic disease|idiopathic]], without a discernible cause.
* Injury: A mild form of myositis can occur with hard exercise.<ref name="Hoffman_2021">{{Cite web | vauthors = Hoffman M | veditors =   DerSarkissian C | date = 19 April 2021 |title=Myositis: Symptoms and Causes |url=https://www.webmd.com/a-to-z-guides/myositis-symptoms-treatments-prognosis |access-date=2022-06-12 |website=WebMD |language=en}}</ref> A more severe form of muscle injury, called [[rhabdomyolysis]], is also associated with myositis.<ref name="Hoffman_2021" /> This is a condition where an  injury to the patient's muscles causes them to quickly break down.<ref name="Hoffman_2021" />
* Medicines: A variety of different medicines can cause myositis. One of the most common types of drugs that can cause myositis are [[statin]]s, which are used to lower cholesterol levels. One of the most common side effects of statin therapy is muscle pain<ref name="Sathasivam_2008">{{cite journal | vauthors = Sathasivam S, Lecky B | title = Statin induced myopathy | journal = BMJ | volume = 337 | pages = a2286 | date = November 2008 | pmid = 18988647 | doi = 10.1136/bmj.a2286 | s2cid = 3239804 }}</ref> which, more rarely, can lead to myositis.<ref name="Sathasivam_2008" />
* Infection: The most common infectious cause of myositis is [[viral infections]], such as the common cold.<ref name="Hoffman_2021" /> Other viruses, such as [[COVID-19]], are also shown to be a rare cause of myositis.<ref>{{cite journal | vauthors = Saud A, Naveen R, Aggarwal R, Gupta L | title = COVID-19 and Myositis: What We Know So Far | journal = Current Rheumatology Reports | volume = 23 | issue = 8 | pages = 63 | date = July 2021 | pmid = 34216297 | pmc = 8254439 | doi = 10.1007/s11926-021-01023-9 }}</ref> [[Benign acute childhood myositis]] has been described in children after prodromal viral infections with different viral agents. [[Bacterial infection|Bacterial]], [[Parasitic infection|parasitic]], and [[fungal infection]]s are other infectious causes of myositis.<ref>{{cite journal | vauthors = Szczęsny P, Świerkocka K, Olesińska M | title = Differential diagnosis of idiopathic inflammatory myopathies in adults - the first step when approaching a patient with muscle weakness | journal = Reumatologia | volume = 56 | issue = 5 | pages = 307–315 | date = 2018 | pmid = 30505013 | pmc = 6263305 | doi = 10.5114/reum.2018.79502 }}</ref> 
* Inherited muscle disease: Many inherited myopathies may have secondary myositis, including [[calpainopathy]], [[dysferlinopathy]], [[facioscapulohumeral muscular dystrophy]], [[dystrophinopathy]], and ''[[LMNA]]''-associated myopathy.<ref>{{cite journal | vauthors = Tarnopolsky MA, Hatcher E, Shupak R | title = Genetic Myopathies Initially Diagnosed and Treated as Inflammatory Myopathy | journal = The Canadian Journal of Neurological Sciences. Le Journal Canadien des Sciences Neurologiques | volume = 43 | issue = 3 | pages = 381–384 | date = May 2016 | pmid = 26911292 | doi = 10.1017/cjn.2015.386 | s2cid = 25515951 | doi-access = free }}</ref>
* Autoimmune: [[Autoimmune disease]] is an abnormal immune response to specific body protein or other biomolecular target, such as one of the muscles. The three main types of idiopathic myositis (known as [[Inflammatory myopathy|inflammatory myopathies]]) that typically test positive for [[autoantibodies]] are [[dermatomyositis]], [[polymyositis]], and [[inclusion body myositis]].<ref name="Hoffman_2021" /> Other autoimmune diseases, such as [[systemic lupus erythematosus]], can also cause myositis-like symptoms.<ref name="Hoffman_2021" />

==Diagnosis==
There are various tools that can be used to help diagnose myositis. The most common methods are physical examination, [[electromyography]] (EMG), [[magnetic resonance imaging]] (MRI), [[muscle biopsy]], and [[blood test]]s. The first course of action a doctor will likely take is perform a physical exam.<ref name="Carstens_2014" /> The doctor assesses for muscle weakness or rashes.

Another possible test is  electromyography. This test involves the insertion of small needles into the patient's muscles.<ref name="Hoffman_2021" /> This allows a physician to look at the muscles' responses to various electrical [[Nerve stimulation|nerve stimuli]] and evaluate which muscles potentially have myositis.<ref name="Hoffman_2021" /> [[Magnetic resonance imaging]] can be useful in diagnosis,<ref>{{cite journal | vauthors = Pipitone N | title = Value of MRI in diagnostics and evaluation of myositis | journal = Current Opinion in Rheumatology | volume = 28 | issue = 6 | pages = 625–630 | date = November 2016 | pmid = 27454210 | doi = 10.1097/BOR.0000000000000326 | s2cid = 25027014 }}</ref> allowing painless, [[Non-invasive procedure|non-invasive]] visualisation of any [[Muscle atrophy|muscle wastage]].<ref name="Hoffman_2021" />

Muscle biopsies, however, are the most reliable tests for diagnosing myositis.<ref name="Hoffman_2021" />

There are also a variety of blood tests available that help in the diagnosis of myositis. The doctor may look for an elevation of [[Lysine carboxypeptidase|creatine kinase]] in the blood, which is indicative of muscle inflammation.<ref name="Hoffman_2021" /> Certain [[Autoantibody|autoantibodies]] (antibodies that target muscle cells) can also be found in the blood, which can indicate that myositis is caused by an autoimmune disease.<ref name="Betteridge_2016" /> Some specific examples of autoantibodies are [[Inflammatory myopathy|Anti-Jo-1]], Anti-HMGCR, Anti-TIF1, etc.<ref name="Betteridge_2016" />

==Treatment==
Treatment for myositis depends on the underlying cause.<ref name="Hoffman_2021" /> For myositis, which is caused by a viral infection, no treatment is typically needed.<ref name="Hoffman_2021" /> For myositis caused by a bacterial infection, antibiotics can be used.<ref name="Hoffman_2021" /> For myositis caused by a medication, it is important to stop using that medication.<ref name="Hoffman_2021" />

There are a variety of treatment options available if myositis is caused by an autoimmune disease. [[Glucocorticoid]]s are often the first choice for treatment.<ref name="Sasaki_2018">{{cite journal | vauthors = Sasaki H, Kohsaka H | title = Current diagnosis and treatment of polymyositis and dermatomyositis | journal = Modern Rheumatology | volume = 28 | issue = 6 | pages = 913–921 | date = November 2018 | pmid = 29669460 | doi = 10.1080/14397595.2018.1467257 | s2cid = 4934267 }}</ref> This drug works to weaken the immune system so that it 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 drug|immunosuppressive]] agent.<ref name="Sasaki_2018" /> This also works to weaken the immune system but does not cause the side effects that  steroids do. Another treatment option is a class of drugs called [[biologics]].<ref name="Sasaki_2018" /> Also, intravenous [[immunoglobulins]] (IVIg) have  been shown to be effective in the treatment of myositis caused by an [[autoimmune disease]].<ref>{{cite journal | vauthors = Mulhearn B, Bruce IN | title = Indications for IVIG in rheumatic diseases | journal = Rheumatology | volume = 54 | issue = 3 | pages = 383–391 | date = March 2015 | pmid = 25406359 | pmc = 4334686 | doi = 10.1093/rheumatology/keu429 }}</ref>

== See also ==
* [[Benign acute childhood myositis]]
* [[Inflammatory myopathy|Inflammatory myopathies]]
* [[Myopathy]] (muscle disease)
* [[Myalgia]] (muscle pain)
* [[Masticatory muscle myositis]] (a disease in dogs)
* [[Perimyositis]]
* [[Sarcoidosis#Bone, joints, and muscles|Sarcoidosis § Bones, joints, and muscles]]

== References ==
{{reflist}}

== External links ==
* [https://www.nlm.nih.gov/medlineplus/myositis.html Myositis]: NIH
{{Medical resources
 | DiseasesDB     = 29473
 | ICD10          = {{ICD10|M|60||m|60}}
 | ICD9           = {{ICD9|729.1}}
 | ICDO           =
 | OMIM           = 160750
 | MedlinePlus    = 001245
 | eMedicineSubj  =
 | eMedicineTopic =
 | MeshID         = D009220
}}

{{Systemic connective tissue disorders}}
{{Myopathy}}

Myositis Association https://www.myositis.org

[[Category:Inflammations]]
[[Category:Muscular disorders]]