Epidemiology of Antisynthetase Syndrome and Risk of Malignancy in a Population-based Cohort (1998-2019)

Objective Population-based epidemiology studies about antisynthetase syndrome (ASSD) are lacking. Our aims were to determine the incidence and prevalence of ASSD and assess malignancy risk among patients following ASSD diagnosis. Methods A retrospective, population-based cohort of adults with incident ASSD residing in Olmsted County, Minnesota, in 1998-2019 was assembled. Fulfillment of ASSD Solomon et al. classification criteria and clinical data were collected by manual chart review. Patients were followed until death, migration from the area, or December 31, 2019. Malignancy was defined by physician diagnosis in the medical record. Incidence rate was age- and sex-adjusted to the 2010 U.S. white population. Point prevalence rate was obtained on Jan 1, 2015. Results 13 patients with ASSD were identified (7 [54%] female, 13 [100%] Caucasian, median age 44.9 years [IQR: 41.9-58.3]). The age- and sex-adjusted incidence of ASSD was 0.56 (95% CI: 0.25-0.87) per 100,000 population. Incidence was highest in the 50-59 age group. Age- and sex-adjusted prevalence was 9.2 per 100,000 (95% CI: 3.4-15.0). 2 of 13 (15%) were diagnosed with malignancy within the follow-up interval; none within 3 years of ASSD diagnosis. At median 11.9 (IQR: 7.0-13.4) years of follow-up, 12/13 (92%) of patients were alive. Conclusion Antisynthetase syndrome is rare, with incidence of 0.56 per 100,000 population and prevalence of 9 per 100,000. In this cohort, incidence was similar between males and females, and highest in persons ages 50-59 years. None of the patients developed malignancy within 3 years of ASSD diagnosis.