Occurrence and Mortality of Stiff Person Syndrome in Denmark

Introduction: Stiff person syndrome is a rare and progressive neurological disorder, yet evidence on long term outcomes is limited. We examined the occurrence and mortality associated with stiff person syndrome in Denmark. Methods: We conducted a population based cohort study including all Danish citizens from 2001–2022. Individuals with a first time diagnosis of stiff person syndrome (N=30) were identified in the Danish National Patient Registry covering all Danish hospitals and matched 1:100 on sex and birth year with persons from the general population (N=3,000). Incidence, prevalence, cumulative mortality, and mortality rates were estimated, and Cox proportional hazards regression was used to compute hazard ratios (HRs) as an estimate of mortality rate ratios adjusted for sex, year of birth, and comorbidity with 95% confidence intervals (CIs). Results: Thirty patients were diagnosed during the study period; 53.3% were male, and median age at diagnosis was 50 years. Incidence increased from 0.11 per 1,000,000 person years (2001–2008) to 0.43 (2017–2022). Prevalence rose from 1.32 per 1,000,000 in 2016 to 3.94 in 2022. The 10 year cumulative mortality in the stiff person syndrome cohort was 27.5% (95% CI: 13.8–50.1) (HR=4.1 [95% CI: 1.9–8.9). Conclusion: Stiff person syndrome is a rare disorder with increasing incidence and prevalence, and high mortality.