Prevalence and baseline characteristics of patients with Generalized Pustular Psoriasis (GPP) in the United States from 2016 to 2025

Objective: The purpose of this study is to estimate the prevalence of GPP in the US between 2016 and 2025 and describe baseline demographic and clinical characteristics of patients with GPP in routine care. Background: Generalized pustular psoriasis (GPP) is a rare, severe, autoinflammatory skin disease characterized by acute flares and systemic manifestations including fever, malaise, and arthralgia. Estimated US prevalence of GPP ranges from 2 to 15 cases per 100,000, highlighting its rarity relative to plaque psoriasis, which affects approximately 3% of U.S. adults.¹⁻³ Most existing evidence on GPP disease burden relies on case reports, case series, and small descriptive studies, and there are very few observational studies based on a representative sample of patients in the US. Methods: Data for this descriptive cohort study were derived from the OM1 Real World Data Cloud (OM1, Inc., Boston, MA), a large, demographically and geographically representative real-world dataset with linked open claims and electronic medical record (EMR) data on patients in the US. The study population included individuals with a first qualifying GPP diagnosis (ICD-10-CM L40.1) during the study period (January 1, 2016, to December 31, 2025). GPP prevalence was estimated and reported as cases per 100,000 persons over the ten-year study period. To address the potential for GPP diagnosis misclassification we performed a sensitivity analysis of the prevalence estimation requiring a second GPP diagnosis code between day 30 and day 365 after the first GPP diagnosis to provide a more conservative prevalence estimate. For the analysis of patient characteristics, patients were required to have no prior GPP diagnosis before 2016, at least 365 days of baseline information and at least 180 days of follow-up. (Figure-1) Results: The estimated prevalence of GPP was 14.6 per 100,000 persons over the 10-year study period. (Figure 3) In sensitivity analyses that required a second GPP diagnosis code, the estimated prevalence was 4.2 cases per 100,000 persons. (Figure 3) The annual prevalence of GPP per 100,000 population more than doubled over the duration of the study period. (Figure 6) The final eligible cohort (N= 8,130) had a mean (SD) age of 57.2 ((standard deviation (SD)) =16.2) years and was predominantly female (66.0%) and White (87.2%). (Figure 2,4) Most patients had commercial insurance (52.3%) and resided in the Southern United States (61.5%). (Figure 4) Patients had a mean (SD) BMI of 30.2 (7.2) kg/m² and a substantial burden of comorbidities, including hypertension (54.1%), dyslipidemia (50.9%), plaque psoriasis (40.9%), anxiety (28.6%), type 2 diabetes (24.7%), depression (27.9%), psoriatic arthritis (17.7%), and coronary artery disease (15.1%) (Figure 4,5) Strengths and limitations: This study leveraged a geographically representative US real-world dataset to identify one of the largest contemporary GPP cohorts over a 10-year period (2016-2025), providing robust and current prevalence estimates while incorporating sensitivity analyses to assess and mitigate potential diagnostic misclassification. GPP case identification relied on diagnosis codes without chart-level validation, creating the potential for misclassification; additionally, the predominance of White patients and inclusion of only diagnosed cases captured within the healthcare system may limit generalizability and could result in underestimation of the true population prevalence. Conclusions: The estimated prevalence of GPP between 2016 and 2025 ranged from 4.2 to 14.6 cases per 100,000 population, depending on the cohort definition, and was generally consistent with estimates reported in prior studies. These findings underscore the rarity of GPP. Given the large geographically representative nature of data source, ten-year study period, and rigorous GPP case identification criteria, this study’s estimates are among the most robust and current estimates of GPP prevalence in the US.This real-world study provides contemporary insights into the prevalence of GPP in the US and baseline demographic and clinical characteristics of patients diagnosed with GPP in routine care. Future work will aim to understand treatment utilization patterns and clinical outcomes in this study population.