Abstract | AIM: To evaluate myositis line immunoassay (LIA) for diagnosis and sub-classification of suspected idiopathic inflammatory myopathy (IIM). To investigate if test performance is improved by increasing signal strength cut-off for myositis-specific antibody (MSA) or combining MSA with indirect immunofluorescence (IIF). METHODS: A retrospective, consecutive case series of patients investigated for MSAs from June 2013 to June 2020 for suspected IIM. Specificity, sensitivity, positive predictive value, and negative predictive value were calculated with 95% confidence intervals for diagnosis of IIM. Association of IIM diagnosis with increased signal strength and presence of an expected IIF pattern on Hep-2 cells was assessed by Fisher's exact test in MSA-positive patients. RESULTS: A total of 195 patients were evaluated. IIM was diagnosed in 32/195 (16.4%) patients. MSAs were detected in 41/195 (21%) patients, 18/41 (43.9%) patients with an MSA had a diagnosis of IIM. The probability of an IIM diagnosis was increased in MSA-positive patients with high compared with low signal strength (83.3% vs 43.5%; P = 0.01) and an expected compared with unexpected IIF pattern (61.5% vs 23.8%; P = 0.04). Specificity for IIM was not significantly improved by increasing signal strength cut-off (85.9% vs 93.8%). Positive predictive value of myositis LIA was only modest and not significantly improved by either increasing signal strength cut-off or requiring an expected IIF pattern for determination of MSA positivity (43.9% vs 60% vs 61.5%). Sub-classification of IIM correlated closely for respective MSAs (88.9%). CONCLUSION: Increased MSA signal strength on myositis LIA and the presence of an expected IIF pattern were associated with IIM diagnosis. Test performance was non-significantly improved by these methods. Prevalence of IIM in this patient cohort was low; it is not excluded that LIA performance could be improved by these methods in a higher prevalence cohort.
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Authors | Thomas J Beaton, David Gillis, Kerri Prain, Karen Morwood, James Anderson, John Goddard, Timothy Baird |
Journal | International journal of rheumatic diseases
(Int J Rheum Dis)
Vol. 24
Issue 9
Pg. 1167-1175
(Sep 2021)
ISSN: 1756-185X [Electronic] England |
PMID | 34250724
(Publication Type: Evaluation Study, Journal Article)
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Copyright | © 2021 Asia Pacific League of Associations for Rheumatology and John Wiley & Sons Australia, Ltd. |
Chemical References |
- Autoantibodies
- Autoantigens
- Biomarkers
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Topics |
- Adult
- Aged
- Aged, 80 and over
- Autoantibodies
(blood)
- Autoantigens
(immunology)
- Biomarkers
(blood)
- Cell Line
- Female
- Fluorescent Antibody Technique
- Humans
- Immunoassay
- Male
- Middle Aged
- Myositis
(blood, classification, diagnosis, immunology)
- Predictive Value of Tests
- Reproducibility of Results
- Retrospective Studies
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