Federica Montagnese1, Haris Babačić2, Peter Eichhorn3, Benedikt Schoser2. 1. Department of Neurology, Friedrich-Baur-Institute, Ludwig-Maximilians-University Munich, Ziemssenstr. 1a, 80336, Munich, Germany. federica.montagnese@med.uni-muenchen.de. 2. Department of Neurology, Friedrich-Baur-Institute, Ludwig-Maximilians-University Munich, Ziemssenstr. 1a, 80336, Munich, Germany. 3. Institute of Laboratory Medicine, University Hospital, LMU Munich, Munich, Germany.
Abstract
BACKGROUND: Myositis-associated antibodies (MAA) and myositis-specific antibodies (MSA) are detected in patients with idiopathic inflammatory myopathies (IIM); their role as diagnostic biomarkers is however still debated. The aim of our study was to assess the utility of MAA/MSA assessed by new line immunoassays in detecting myositis among neuromuscular patients. METHODS: We retrospectively analysed sera samples obtained from patients tested for myositis antibodies with the "Euroline: Autoimmune Inflammatory Myopathies 16Ag" and "myositis profile 3" kits (Mi-2, TIF1γ, MDA5, NXP2, SAE1, Jo-1, SRP, PL-7/12, EJ, OJ, Ro-52, Ku, PM-Scl75/100). First symptom, CK, EMG, muscle biopsy and diagnosis were also analysed. Using logistic regression analysis, two diagnostic models were built to evaluate the diagnostic power of MAA/MSA in distinguishing myositis patients from controls and other myopathies. RESULTS: 1229 patients were identified. 141 patients had a bioptic confirmed IIM; other diagnoses included: myopathy (n = 357), other neuromuscular diseases (n = 144) and no neuromuscular diseases (n = 587). The specificity was 95% for MSA and 89% for MAA, the sensitivity 20% and 22%, respectively. MAA showed no use in differentiating myositis patients from controls, whereas MSA had limited effect (OR = 5.165), compared to other variables as EMG (OR = 47.755) or CK > 2000 U/L (OR = 45.307). MSA were, however, the most useful parameter differentiating IIM from non-IIM patients (OR = 7.259), better than CK > 2000 U/L (OR = 4.033) and MAA (OR = 2.737). CONCLUSIONS: Line immunoassays for myositis antibodies show high specificity but low sensitivity. Their usefulness as diagnostic biomarkers widely depends on the clinical settings. Our study suggests that MSA/MAA should be used for confirmatory and differential diagnosis rather than for screening purposes in inflammatory myopathies.
BACKGROUND: Myositis-associated antibodies (MAA) and myositis-specific antibodies (MSA) are detected in patients with idiopathic inflammatory myopathies (IIM); their role as diagnostic biomarkers is however still debated. The aim of our study was to assess the utility of MAA/MSA assessed by new line immunoassays in detecting myositis among neuromuscular patients. METHODS: We retrospectively analysed sera samples obtained from patients tested for myositis antibodies with the "Euroline: Autoimmune Inflammatory Myopathies 16Ag" and "myositis profile 3" kits (Mi-2, TIF1γ, MDA5, NXP2, SAE1, Jo-1, SRP, PL-7/12, EJ, OJ, Ro-52, Ku, PM-Scl75/100). First symptom, CK, EMG, muscle biopsy and diagnosis were also analysed. Using logistic regression analysis, two diagnostic models were built to evaluate the diagnostic power of MAA/MSA in distinguishing myositis patients from controls and other myopathies. RESULTS: 1229 patients were identified. 141 patients had a bioptic confirmed IIM; other diagnoses included: myopathy (n = 357), other neuromuscular diseases (n = 144) and no neuromuscular diseases (n = 587). The specificity was 95% for MSA and 89% for MAA, the sensitivity 20% and 22%, respectively. MAA showed no use in differentiating myositis patients from controls, whereas MSA had limited effect (OR = 5.165), compared to other variables as EMG (OR = 47.755) or CK > 2000 U/L (OR = 45.307). MSA were, however, the most useful parameter differentiating IIM from non-IIM patients (OR = 7.259), better than CK > 2000 U/L (OR = 4.033) and MAA (OR = 2.737). CONCLUSIONS: Line immunoassays for myositis antibodies show high specificity but low sensitivity. Their usefulness as diagnostic biomarkers widely depends on the clinical settings. Our study suggests that MSA/MAA should be used for confirmatory and differential diagnosis rather than for screening purposes in inflammatory myopathies.
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