Background/Purpose: The antisynthetase syndrome (ASSD) is a distinct subgroup of the idiopathic inflammatory myopathies characterized by myositis, interstitial lung disease, inflammatory arthritis, Raynaud’s phenomenon and an aminoacyl tRNA synthetase autoantibody. Population-based epidemiology studies are lacking. Our aims were to determine the incidence and prevalence of ASSD in a well-defined geographic area over a 22-year period, and to assess malignancy risk among incident ASSD patients within 3 years of diagnosis.

Methods: A retrospective, population-based cohort of adult patients with incident ASSD in a geographically well-defined area from Jan 1, 1998 to Dec 31, 2019 was assembled. Fulfillment of Solomon et al. criteria (1) and clinical data were collected by manual chart review via a validated medical records linkage system. Malignancy was defined by physician diagnosis in the medical record. Patients were followed until death, migration from the area, or December 31, 2019. 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 who fulfilled Solomon et al. criteria were identified in the 22-year study period. 7 (54%) were female, 13 (100%) Caucasian, median age 44.9 years (IQR: 41.9, 58.3) at time of meeting criteria.

At time of meeting criteria, 11 (85%) of patients had interstitial lung disease diagnosed by a physician. Of these 8 patients (73%) had an NSIP pattern. 11 patients (85%) had myositis: 6/12 (50%) had a positive EMG, 1 (8%) with a positive muscle MRI. 5 patients had muscle biopsy performed, and 100% demonstrated inflammatory myopathy. 13 (100%) had positive anti-nuclear antibody; 12 (92%) had positive Jo-1 antibody. A myositis-specific panel was positive in 1 out of 4 patients showing PL-7 antibody.

The age- and sex-adjusted incidence of ASSD was 0.56 (95% CI: 0.25-0.87) per 100,000 population. The age-adjusted incidence was 0.59 (95% CI: 0.15-1.03) per 100,000 for females, and 0.52 (95% CI: 0.10-0.94) per 100,000 for males. Incidence rate was highest in the 50-59 age group, at 1.01 per 100,000 population. Age- and sex- adjusted prevalence of ASSD on Jan 1, 2015 was 9.2 per 100,000 (95% CI: 3.4-15.0).

2/13 (15%) were diagnosed with a malignancy (Hodgkin’s lymphoma, leiomyosarcoma) within the follow-up interval; none within 3 years of ASSD diagnosis. Mean time to malignancy diagnosis from ASSD criteria was 52 (range: 40-64) months.

At a 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. Incidence appears similar in our cohort between males and females, differing from previous estimates of higher incidence in females, and highest in persons age 50-59. None of the patients in this cohort developed malignancy within 3 years of ASSD diagnosis.

(1) Solomon J, Swigris JJ, Brown KK. Myositis-related interstitial lung disease and antisynthetase syndrome. J Bras Pneumol. 2011;37(1):100-109.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/incidence-of-antisynthetase-syndrome-and-risk-of-malignancy-in-a-population-based-cohort-1998-2019/