G.P.62 Myositis-associated, myositis-specific and organ-specific autoantibodies in inflammatory myopathies: A West Australian population control study

Abstract

<h2>Abstract</h2> The prevalence of autoantibodies (AAb) in inflammatory myopathies (IMs) is known to vary in different geographic regions and population groups. A limitation of previous AAb prevalence studies in the IMs has been the lack of a population control group in most studies. In the present study, the frequencies of non-organ specific myositis-associated AAbs (MAA) [ANA, ENA, anti-PM-Scl 75, anti-PM-Scl 100, anti-Ku]; myositis-specific AAbs (MSA) [anti-EJ, anti-OJ, anti-Pl-12, anti-PL7, anti-Jo-1, anti-SRP and anti-Mi-2]; and organ-specific thyroid [anti-TPO] and celiac AABs [IgA anti-tTg] were compared in 125 biopsy proven cases of IM[s-IBM 52, DM 29, Overlap Syndrome (OS) 25, NAM 10, PM 9] diagnosed in the Myositis Clinic at the ANRI and a Western Australian control group of 198 individuals from the Busselton Population Health Study. The patient and control sera were all tested in the PathWest Immunology Laboratories using identical techniques. One or more AAbs were present in 62% of the IM patients compared with 12% of controls. ANA was the most common AAb in all IM groups, being highest in frequency in OS and lowest in s-IBM, and was also present in lower titre in 10% of controls. The frequency of anti-Ro52 was also higher in all IM groups except NAM, while anti-TPO and anti-tTg were similar in IM and controls. The frequency of MSAs was higher in PM (44%), DM (30%) and OS (27%) than in s-IBM (14%), and 10% of the control group also had low titres of a MSA. Anti-Jo-1 was the most frequent MSA across the groups, being present in 8% of all IM cases, but was also present in 3% of controls. Our findings in this population indicate that MAA and MSA are more frequent in DM, PM and OS than in s-IBM and demonstrate the importance of having reference figures for frequency and antibody titre from an appropriate population control group in interpreting the results of AAb studies in patients with IM.