AB0822 A measurement of anti-ars antibodies, anti-mi-2 antibody, anti-tif1 gamma antibody and anti-mda5 antibody by enzyme-linked immunosorbent assay as a diagnostic tool of idiopathic inflammatory myopathyat rheumatology daily practice
Authors: Y. Miyoshi, T. Kise, N. Yokogawa, K. Shimada, S. Sugii
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Enzyme-linked immunosorbent assay (ELISA) tests of anti-ARS antibodies, anti-Mi-2 antibody, anti-TIF1γ antibody and anti- MDA5 antibody became available at daily clinical practice on <sup>Oct. 2016</sup> in Japan. Diagnostic accuracy study of myositis-specific autoantibodies (MSAs) except for anti-Jo-1 antibody in daily clinical practice is scarce[.<sup>1</sup> <h3>Objectives</h3> This study investigated the diagnostic utility of newly available myositis-specific autoantibodies (ELISA) in idiopathic inflammatory myopathy (IIM) suspected patients at a rheumatology clinic with muscle and skin biopsy as a reference standard. <h3>Methods</h3> This study is a retrospective, cross-sectional study. The electrical medical records of patients who visited the department of rheumatic diseases at <sup>Tokyo Metropolitan Tama Medical Centre between Nov. 2016</sup> and <sup>Aug. 2017</sup> were retrospectively searched for clinical variables and laboratory data. Patients with serum creatine phosphokinase (CK) greater than two-fold of normal upper limit (over 300 IU/ml) or suspected dermatomyositis skin rash were included. Anti-ARS antibodies, anti-Mi-2 antibody, anti-TIF1γ antibody and anti-MDA5 antibody were measured by ELISA[.<sup>2–4</sup> Two muscle pathologists interpreted muscle biopsy. The skin biopsies with interface-dermatitis were considered positive. The biopsy results of patients who did not have biopsy procedure but whose symptoms and signs improved without immunosuppressive therapy were assumed negative. IIM diagnosis was based on 2017 EULAR/ACR classification criteria[.<sup>5</sup> We calculated likelihood ratio of MSAs for biopsy results and IIM diagnosis. <h3>Results</h3> Eight hundred and eighty-six new patients visited an outpatient clinic of rheumatic disease department and 38 patients met inclusion criteria. 14 patients were excluded because of apparent causes (1 each for sepsis, rhabdomyolysis, macro CK, serotonin syndrome, motor neuron disease, statin myopathy, SSc, idiopathic IP, seborrheic dermatitis, 3 for symptoms not compatible with IIMs.) and no biopsy results (2 patients). 17 (71%) of 24 patients analyses were female. The median age was 56.5 (IQR 41–65) years, median CK 658 (IQR 105–1866) IU/ml. 11 (46%)patients had the positive biopsy result (6 muscle biopsy and 5 skin biopsy) and IIM diagnosis. 10 (42%) patients were positive for MSAs (anti-ARS antibodies in 3, anti-Mi-2 antibody in 1, anti- TIF1γ antibody in2, anti-MDA5 antibody in 3 and double positive for anti-ARS and anti-MDA5 antibody in 1). The positive likelihood ratio of MSAs for the biopsy result and IIM diagnosis was ∞ (95% CI cannot be calculated). The negative likelihood ratio was 0.091 (95% CI 0.086–0.097). <h3>Conclusions</h3> Our analysis demonstrated that MSAs measured by ELISA efficiently differentiated biopsy-proven IIMs from other medical conditions at rheumatology daily practice. <h3>References</h3> [1] Satoh, M., et al., Clin Rev Allergy Immunol, 2017. 52(1): p. 1–19. [2] Sato, S., et al., PLoS One, 2016. 11(4): p. e0154285. [3] Nakashima, R., et al., PLoS One, 2014. 9(1): p. e85062. [4] Fujimoto, M., et al., J Dermatol Sci, 2016. 84(3): p. 272–281. [5] Lundberg, I.E., et al., Arthritis Rheumatol, 2017. 69(12): p. 2271–2282 <h3>Disclosure of Interest</h3> None declared