Incidence and prevalence of generalised pustular psoriasis in multi-ethnic Johor Bahru, Malaysia: a population-based cohort study using routinely captured electronic health records in Teleprimary Care (TPC®) clinical information system from 2010 to 2020

There is limited understanding of the epidemiology of generalised pustular psoriasis (GPP) internationally, with no population-based estimates of GPP in Southeast Asia. To determine the incidence and prevalence of GPP in the Malaysian population and characterise its flares and trigger factors. A population-based cohort study using the Teleprimary Care database between January 2010 and December 2020. We identified 230 dermatologist-confirmed GPP cases by ICD-10 diagnostic codes. Annual prevalence and incidence rates were stratified by age, gender, and ethnicity. Flares and trigger factors were compared between GPP patients with and without associated psoriasis vulgaris (PV). The prevalence of GPP per million was 198 (women, 267; men, 127) and incidence was 27.2 per million person-years (95% CI 22.8-31.6); women 35.3 (28.4-42.2), men 18.3 (13.1-23.5). Rates were higher in Chinese (prevalence 271 per million; incidence 41.6 per million person-years [28.9-54.3]) than in Malays (prevalence 186; incidence 24.6 [19.4-29.7]) or Indians (prevalence 179; incidence 25.0 [13.8-36.3]). Annual prevalence was consistently higher in women than men and highest amongst the Chinese population, followed by Indians and Malays. Sixty-seven percent of GPP patients had associated PV. The prevalence and incidence of GPP without PV were lower than GPP with PV at 66 vs 132 per million and 19.3 (95% CI 15.6-23.0) vs 8.0 (95% CI 5.6-10.3) per million person-years, respectively. The mean age (±SD) at GPP onset was 42.7±18.4 years. A bimodal trend in the age of GPP onset was observed, with first and second peaks at 20-29 and 50-59 years of age, respectively. Disease onset was significantly earlier in GPP patients without than those with PV (mean age; 37.5±20.7 vs 44.9±17.0 years, P=0.026). Flares occurred more frequently in patients without than with PV (mean flares/patient/year was 1.35±0.77 vs 1.25±0.58, P=0.039). Common triggers of flares in GPP patients without PV were infections, pregnancy, menstruation, and stress, whereas withdrawal of therapy, particularly systemic corticosteroids, was a more frequent trigger in GPP patients with PV. Our findings contribute to the global mapping of GPP, which will help inform the management of this rare condition.