Seasonal patterns of myositis-specific and myositis-associated autoantibodies in Italy

Objective: Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of systemic autoimmune disorders affecting skeletal muscles but also other organs. There are different forms of IIM, each with peculiar clinical manifestations and prognosis. Accordingly, several autoantibodies have been described in IIM, with different prevalence in the different forms of the disease. The etiopathogenesis of IIM is still unclear, although environmental agents play certainly a role to trigger disease development in genetically predisposed individuals. Supporting this notion, some reports suggest that the incidence of IIM may be different throughout the year. In this work, we tested if the detection of autoantibodies typically observed in IIM has a seasonal pattern. Methods: We collected serological data from line immunoassays (LIA) performed on 4277 patients with suspected IIM from January 2018 to December 2020 in ten Italian hospitals. Myositis-specific and myositis-associated autoantibodies were evaluated by line-immunoassay. Results: Our findings demonstrate that absolute numbers of anti-MDA5, anti-PM-Scl75, anti-Mi2b and anti-TIF1ɣ autoantibodies are more frequently detected in autumn-winter than in spring-summer. However, only anti-PM-Scl75 and anti-MDA5 display a similar pattern when analyzing frequencies of positive tests (for anti-PM-Scl75 100 positive tests and 2107 negative tests from September to February; 55 positive tests and 1903 negative tests from March to August, p = 0.003; for anti-MDA5 34 positive tests and 1983 negative tests from September to February; 17 positive tests and 1760 negative tests from March to August, p = 0.051). Conclusions: These findings suggests that triggering agents promoting the development of these autoantibodies have a specific seasonal pattern.