Population-Based Study of the Epidemiology of Stiff Person Syndrome in a Large Colorado-Based Health System.

Background And Objectives: Stiff person syndrome spectrum disorder (SPSD) is a rare autoimmune disorder characterized by progressive muscle stiffness and painful spasms with an estimated prevalence of 1-2 cases per million people. Population-based epidemiologic studies are lacking because of both poor patient capture and the lack of standardized diagnostic criteria. Objectives of this study were to describe the incidence and prevalence of SPSD within the University of Colorado Health (UCH) system and apply previously proposed published criteria for SPSD within this population.

Methods: We queried Health Data Compass, an electronic health data repository for a large academic health care system, from 2012 through 2022 for all patients older than 18 years with () codes pertaining to stiff person syndrome. Records were reviewed for diagnostic confirmation. We calculated yearly and period prevalence and incidence rates based on observable person-time exposure of our cohort. We applied previously published Mayo Clinic and Johns Hopkins criteria for SPSD and compared period prevalence based on each criterion and evaluated for agreement.

Results: Two hundred and seventy-three patients met the initial inclusion criteria using codes; 59 were confirmed to have SPSD. The mean age was 49.7 years (SD = 12.9), 59.3% were female, 59.3% were considered antibody positive. The total database population over the interval was 2,801,674 persons. The estimated prevalence of SPSD based on our UCH cohort was 2.11 (95% CI 1.57-2.64) per 100,000 persons. The average yearly incidence was 0.35 per 100,000 person-years (95% CI 0.27-0.46). Applying different clinical diagnostic criteria, the estimated prevalence ranged from 1.36 (95% CI 0.93-1.79) to 1.82 (95% CI 1.32-2.32) per 100,000 persons.

Discussion: We describe a prevalence of SPSD of 2.11 per 100,000 persons in our UCH cohort. Prevalence estimates differed depending on which clinical diagnostic criteria were applied and whether possible SPSD cases were included. Using the most stringent criteria for diagnosis, we report a prevalence of 1.36 per 100,000 persons. While our study uniquely captures many US demographic groups, limitations remain because this is a retrospective review of a single system. Additional studies are needed to determine whether these results are representative of a national or global population.