Not One-in-a-million: A Single-Center Case Series of Patients with Stiff Person Syndrome

ObjectiveDescribe the epidemiology of stiff person syndrome (SPS) patients seen at a large academic health system. BackgroundSPS is a rare autoimmune disorder characterized by progressive muscle stiffness and painful spasms estimated to occur in 1-2 per million people within the US, although large, population-based epidemiological studies are lacking. While proposed diagnostic criteria exist, there are no standardized international consensus criteria. Design/MethodsWe queried Health Data Compass, a linked dataset connecting EHRs from a single academic health care system with the Colorado All Payers Claim Database from 2012 through 2022 for all patients ≥ 18-year-old with ICD-10 codes pertaining to Stiff Person Syndrome [G25.82] with subsequent record review for diagnostic confirmation. Proposed diagnostic criteria applied to understand the sensitivity of these criteria in our cohort and to evaluate the agreement among criteria. Results273 patients met initial inclusion criteria using ICD-10 codes. 66 patients were confirmed to have SPS based on chart review. The database population over the interval was 2,802,246 persons. Prevalence for SPS was 2.36 per 100,000 persons (95% CI:(8.18405, 10.4439)). The mean age of patients was 51.1 years (SD=13.4), 60.6% were female, and 78.8% Caucasian, 12.1% Black, and 10 % other. 62% were considered antibody positive (either serum GAD 65 IgG > 20 nmol/L, serum GAD 65 IgG > 10,000 IU/mL, CSF GAD 65 IgG positive, GlyR IgG positive, or amphiphysin IgG positive). Estimated prevalence of SPS within this cohort is 2.36 (95% CI 1.79-2.92) per 100,000 persons. Accounting for differences in diagnostic criteria, the estimated prevalence ranges from 1.28 (95% CI 0.87-1.70) to 2.36 (95% CI 1.79-2.92) per 100,000 persons. ConclusionsUnderstanding the true disease burden of SPS is fundamental to ensuring optimal patient care, allocating appropriate system resources, and to improve upon current treatment standards. We identified a prevalence of 2.36 per 100,000 persons, greatly exceeding previous descriptions.