Editing Inclusion body myositis (section)

==Diagnosis==
[[File:Inclusion body myositis histology.jpg|thumb|right|Inclusion body myositis histology]]

Elevated [[creatine kinase]] (CK) levels in the blood (at most ~10 times normal) are typical in sIBM but affected individuals can also present with normal CK levels. [[Electromyography]] (EMG) studies display variable abnormalities such as increased insertional activity,<ref>{{Cite journal |last1=Moghadam-Kia |first1=Siamak |last2=Oddis |first2=Chester V. |last3=Aggarwal |first3=Rohit |date=2016 |title=Approach to asymptomatic creatine kinase elevation |journal=Cleveland Clinic Journal of Medicine |language=en |volume=83 |issue=1 |pages=37–42 |doi=10.3949/ccjm.83a.14120 |pmid=26760521 |pmc=4871266 |issn=0891-1150}}</ref> increased spontaneous activity (fibrillation potentials and sharp waves),<ref name="Weihl2019Review" /> and large/broad or short/narrow motor unit potentials.<ref name="Weihl2019Review" /> On EMG, recruitment patterns can be reduced or increased. Findings can vary even within the same muscle of an affected individual.<ref name="Weihl2019Review" /> Muscle biopsy may display several common findings including inflammatory cells invading muscle cells, vacuolar degeneration, and [[inclusion bodies]] of aggregations of multiple proteins.<ref name="NORD">{{cite web |title=Sporadic Inclusion Body Myositis |url=https://rarediseases.org/rare-diseases/sporadic-inclusion-body-myositis/ |website=NORD (National Organization for Rare Disorders)}}</ref> sIBM is a challenge to the pathologist and even with a biopsy, diagnosis can be ambiguous.<ref>{{Cite web |title=muscle biopsy revealed: Topics by Science.gov |url=https://www.science.gov/topicpages/m/muscle+biopsy+revealed.html |access-date=2022-10-28 |website=www.science.gov}}</ref>

A diagnosis of inclusion body myositis was historically dependent on muscle biopsy results. Antibodies to cytoplasmic 5'-nucleotidase (cN1A; [[NT5C1A]]) have been strongly associated with the condition.<ref name="Weihl2019Review" /> However, other inflammatory conditions, such as lupus, can have a positive anti-NT5C1A.<ref name="Weihl2019Review" /> As of 2019, it remains to be established whether a positive anti-NT5C1A antibody test can make muscle biopsy unneeded.<ref name="Weihl2019Review" />
[[File:Inclusion body myositis MRI.jpg|thumb|left|Inclusion body myositis MRI]]

Muscle imaging can help establish the pattern of muscle involvement and selection of a biopsy site.<ref name="Weihl2019Review" />

===Differential diagnosis===
IBM is often initially misdiagnosed as [[polymyositis]]. A course of [[prednisone]] is typically completed with no improvement and eventually, sIBM is confirmed. sIBM weakness comes on over months or years and progresses steadily, whereas polymyositis has an onset of weeks or months. [[Muscular dystrophy]] (e.g., [[limb girdle muscular dystrophy]]) must be considered as well.{{citation needed|date=February 2021}} sIBM can be mistaken for physical deconditioning.<ref name="Weihl2019Review" />

Hereditary myopathies can mimic sIBM, both in signs and symptoms and in the appearance of muscle biopsies. A small percentage of those initially diagnosed with sIBM are later found to have pathogenic mutations in the genes ''[[Valosin-containing protein|VCP]]'' and ''[[SQSTM1]]'', which are known to cause hIBM.<ref name="Weihl2019Review" />

IBM has a distinctive pattern of muscle involvement that distinguishes it among inflammatory myopathies.<ref name="Greenberg2019Review" /> Characteristic of IBM is weakness of finger flexion, knee extension, and ankle dorsiflexion.<ref name="Greenberg2019Review" /> Other inflammatory myopathies cause a proximal muscle weakness pattern, such as weakness of hip flexion, abduction, and extension, as well as shoulder abduction.<ref name="Greenberg2019Review" /> IBM and other inflammatory myopathies both cause bicep/tricep weakness.<ref name="Greenberg2019Review" />

===Classification===
* The common type is sIBM; it strikes individuals apparently at random.<ref>{{cite journal |vauthors=Karpati G, O'Ferrall EK | date = Jan 2009 | title = Sporadic inclusion body myositis: Pathogenic considerations| journal = Ann Neurol | volume = 65 | issue = 1| pages = 7–11 | doi=10.1002/ana.21622| pmid = 19194875 | s2cid = 41203262 }}</ref>
* There is a type that has been observed in multiple siblings in the same generation in several families, termed ''familial inflammatory sIBM'', but it is not passed on from generation to generation.<ref name="pmid16932602" />
* There are also several very rare forms of ''hereditary inclusion body myopathy'' (hIBM) that are linked to specific genetic defects and that are passed on from generation to generation, each inherited in different ways.<ref>{{cite journal |author1=Broccolini A. |author2=Mirabella M. | year = 2014 | title = Hereditary inclusion-body myopathies | journal = Biochim. Biophys. Acta | volume = 1852| issue = 4| pages = 644–650| doi = 10.1016/j.bbadis.2014.08.007 | pmid=25149037| doi-access = free }}</ref>