Polymyositis and dermatomyositis laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]

Overview

An elevated/reduced concentration of serum/blood/urinary/CSF/other [lab test] is diagnostic of [disease name].

OR

Laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].

OR

[Test] is usually normal for patients with [disease name].

OR

Some patients with [disease name] may have elevated/reduced concentration of [test], which is usually suggestive of [progression/complication].

OR

There are no diagnostic laboratory findings associated with [disease name].

Different laboratory tests may be used to diagnose polymyositis and dermatomyositis and exclude other myopathies which include:^[1]^[2]
- Sarcoplasmic enzymes
- Myositis-specific autoantibodies

Sarcoplasmic enzymes consistent with the diagnosis of polymyositis and dermatomyositis include:^[3]

Autoantibody	Association	Percentage
Histidyl-tRNA synthetase (anti-Jo-1)	Antisynthetase syndrome Flare up in spring Epstein-Barr virus (EBV), adenovirus, and influenza infection
Chromodomain helicase DNA binding protein 4 (Mi-2)	Severe dermatomyositis rash without significant lung involvement
Signal recognition particle (anti-SRP)	Flare up in fall
Alanyl-tRNA synthetase (PL-12)	Epstein-Barr virus (EBV), adenovirus, and influenza infection
Transcriptional intermediary factor 1-gamma (TIF-1γ)	Cancer-associated myositis Juvenile dermatomyositis
Nuclear matrix protein (NXP-2)	Cancer-associated myositis Juvenile dermatomyositis
Anti-small ubiquitin-like modifier activating enzyme (anti-SAE)	Cancer-associated myositis
Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR)	Statin-associated necrotizing autoimmune myopathy (SANAM)	6%

↑ Adler BL, Christopher-Stine L (February 2018). "Triggers of inflammatory myopathy: insights into pathogenesis". Discov Med. 25 (136): 75–83. PMID 29579414.
↑ Bodoki L, Nagy-Vincze M, Griger Z, Betteridge Z, Szöllősi L, Dankó K (December 2014). "Four dermatomyositis-specific autoantibodies-anti-TIF1γ, anti-NXP2, anti-SAE and anti-MDA5-in adult and juvenile patients with idiopathic inflammatory myopathies in a Hungarian cohort". Autoimmun Rev. 13 (12): 1211–9. doi:10.1016/j.autrev.2014.08.011. PMID 25182203.
↑ Bohan, Anthony; Peter, James B. (1975). "Polymyositis and Dermatomyositis". New England Journal of Medicine. 292 (8): 403–407. doi:10.1056/NEJM197502202920807. ISSN 0028-4793.