Date: Sunday, November 7, 2021
Session Title: Muscle Biology, Myositis & Myopathies Poster (0683–0722)
Session Type: Poster Session B
Session Time: 8:30AM-10:30AM
Background/Purpose: The skeletal muscle biopsy is the gold standard for idiopathic inflammatory myopathies (IIM) diagnosis. Myositis specific antibodies are diagnostic biomarkers for IIM but are present in only 60-70% of cases. Another non-invasive procedure: the electromyogram (EMG) maybe useful for IIM diagnosis but its diagnostic accuracy has been poorly investigated.
We aim to define the sensitivity, the specificity, and the positive and negative predictive values of EMG for IIM diagnosis.
Methods: We conducted a single-center retrospective study between January 2018 and October 2020. We selected all consecutive patients referred to the neuropathology department for a suspicion of IIM. Patients were enrolled if an EMG was performed in our department before the muscle biopsy.
Patients were diagnosed as IIM based on myopathological finding. Patients were subclassified into dermatomyositis (DM), anti-synthetase syndrome (ASyS), overlap myositis (OM), immune mediated necrotizing myopathy (IMNM), Inclusion body myositis (IBM) and immune checkpoint inhibitor induced myositis (ICI) based on ENMC criteria.
Results: Two hundred and thirty-one patients were screened and 182 patients were included. Patients were 57.8 ± 15.8 years and 62.6% were female.
EMG was described as myogenic in 74.1% of cases. Patients were diagnosed as IIM in 86.2% of cases.
The sensitivity was 82.2%, and the specificity was 76%. The positive likelihood ratio was 3.4. The positive predictive value was 95.6% and the negative predictive value 40.4%.
The presence of EMG abnormality was highly dependent on the IIM subgroup. The sensitivity was high in DM (90%), ASyS (93.8%) and IMNM (95%). The sensitivity also high in sIBM (85.2%) and in OM (85.1%) but low in ICI myositis (29.4%) (Table1).
Statistical analysis showed that factors associated with a false negative EMG (patients; n=28) were the use of corticosteroids prior to EMG (21.7% vs 46.4% p=0.01) and the absence of myositis specific antibody (68% vs. 88.9% p=0.03).
Conclusion: EMG was sensitive and specific for IIM diagnosis but its accuracy decrease with the use corticosteroids.
To cite this abstract in AMA style:bolko L, Leonard Louis S, Salmon J, Benveniste O, Allenbach Y, Maisonobe T. Diagnostic Accuracy of Electromyogram for Myositis [abstract]. Arthritis Rheumatol. 2021; 73 (suppl 10). https://acrabstracts.org/abstract/diagnostic-accuracy-of-electromyogram-for-myositis/. Accessed January 28, 2022.
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