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Background: There is limited understanding of the epidemiology of generalized pustular psoriasis (GPP) internationally, with no population-based estimates of GPP in South East Asia., Objectives: To determine the incidence and prevalence of GPP in the Malaysian population and characterize its flares and trigger factors., Methods: We conducted a population-based cohort study using the Teleprimary Care database between January 2010 and December 2020. We identified 230 dermatologist-confirmed GPP cases using International Classification of Diseases, 10th revision, diagnostic codes. Annual prevalence and incidence rates were stratified by age, sex and ethnicity. We compared data regarding flares and trigger factors for patients with GPP who had associated psoriasis vulgaris (PV) with those who did not have associated PV., Results: The prevalence of GPP was 198 per million (267 women, 127 men) and incidence was 27.2 per million person-years [95% confidence interval (CI) 22.8-31.6]; 35.3 (28.4-42.2) per million person-years for women and 18.3 (13.1-23.5) per million person-years for men. Rates were higher in Chinese individuals [prevalence 271 per million; incidence 41.6 per million person-years (28.9-54.3)] than in the Malay population [prevalence 186; incidence 24.6 (19.4-29.7)] or the Indian ethnic group [prevalence 179; incidence 25.0 (13.8-36.3)]. Annual prevalence was consistently higher in women than in men and highest among the Chinese population, followed by the Indian and Malay populations. Overall, 67% of patients with GPP 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 at GPP onset was 42.7 years (SD 18.4). A bimodal trend in the age of GPP onset was observed, with first and second peaks at age 20-29 years and age 50-59 years, respectively. Disease onset was significantly earlier in patients with GPP without PV than in those with PV [mean age 37.5 years (SD 20.7) vs. 44.9 years (SD 17.0), P = 0.026]. Flares occurred more frequently in patients without PV than in those with PV [mean number of flares per patient per year was 1.35 (SD 0.77) vs. 1.25 (SD 0.58), P = 0.039]. Common triggers of flares in patients with GPP who did not have PV were infections, pregnancy, menstruation and stress, whereas withdrawal of therapy, particularly systemic corticosteroids, was a more frequent trigger in patients with GPP who also had PV., Conclusions: Our findings contribute to the global mapping of GPP, which will help inform the management of this rare condition., Competing Interests: Conflicts of interest: S.E.C. declares paid activities as advisor, speaker or consultant for AbbVie, Boehringer Ingelheim, Eli Lilly, Janssen, LEO Pharma, MSD, Novartis, Pfizer, Sanofi and UCB. C.E.M.G. has received honoraria and/or research grants from AbbVie, Almirall, Amgen, AnaptysBio, Boehringer Ingelheim, Bristol Myers Squibb, Eli Lilly, Evelo Bioscience, Galderma, GSK, Inmagene, LEO Pharma, Janssen, ONO Pharmaceuticals, Novartis, Pfizer, Sandoz and UCB Pharma. D.M.A. reports research grants from AbbVie, Almirall, Eli Lilly, Janssen, Novartis, UCB, and the LEO Foundation., (© The Author(s) 2023. Published by Oxford University Press on behalf of British Association of Dermatologists.)

Background: There are no population-based epidemiological data on psoriasis in Southeast Asia, including Malaysia., Objectives: To determine the incidence and prevalence of psoriasis over 11 years in multiethnic Johor Bahru, Malaysia., Methods: A population-based cohort study was made using the Teleprimary Care database between January 2010 and December 2020. Cases of psoriasis, identified by ICD-10 diagnostic codes, were validated by dermatologists. Annual prevalence and incidence were estimated and stratified by age, sex and ethnicity., Results: We identified 3932 people with dermatologist-confirmed psoriasis, including 1830 incident cases, among 1 164 724 Malaysians, yielding an 11-year prevalence of 0·34% [95% confidence interval (CI) 0·33-0·35] and incidence of 34·2 per 100 000 person-years (95% CI 32·6-35·8). Rates were higher in Indian patients; the prevalences were 0·54% (0·50-0·58) in Indian, 0·38% (0·36-0·40) in Chinese and 0·29% (0·28-0·30) in Malay patients, and the respective incidences per 100 000 person-years were 52·5 (47·3-57·7), 38·0 (34·1-41·8) and 30·0 (28·2-31·8). Rates were higher in males; the prevalence was 0·39% (0·37-0·41) in males and 0·29% (0·27-0·30) in females, and the respective incidences per 100 000 person-years were 40·7 (38·2-43·2) and 28·3 (26·4-30·3). Between 2010 and 2020, annual psoriasis prevalence and incidence increased steadily from 0·27% to 0·51% and from 27·8 to 60·9 per 100 000 person-years, respectively. Annual rates were consistently higher in male and Indian patients. Overall, psoriasis was significantly more common in males than females [odds ratio (OR) 1·37, 95% CI 1·29-1·46] and in Indian and Chinese patients vs. Malay (OR 1·85, 1·71-2·01 and OR 1·30, 1·20-1·41, respectively). Prevalence increased with age, with the highest rates in the groups aged 50-59 and 60-69 years at 0·67% and 0·66%, respectively. A modest bimodal trend in age of psoriasis onset was observed, with first and second peaks at 20-29 and 50-59 years. Disease onset was significantly earlier in females than males [mean (SD) 36·8 (17·3) vs. 42·0 (17·2) years, P < 0·001] and in Malay vs. Indian and Chinese patients [mean (SD): Malay 36·4 (17·5), Indian 40·8 (15·2), Chinese 47·4 (16·9) years, P < 0·001]., Conclusions: We found that psoriasis incidence and prevalence are increasing and varied by age, sex and ethnicity. Our findings should help inform healthcare planning and management for patients with psoriasis in Malaysia. What is already known about this topic? The incidence and prevalence of psoriasis are generally lower in Asian populations and children. There is a lack of agreement on sex-specific differences in psoriasis incidence and prevalence. There has been no population-based study on the incidence and prevalence of psoriasis in Southeast Asia, including Malaysia. There is no information on differences in psoriasis prevalence and incidence by sex, age and ethnicity in Malaysia. What does this study add? Psoriasis incidence and prevalence are increasing in the multiethnic population of Johor Bahru, Malaysia. Incidence and prevalence rates were higher in male than female patients and were consistently highest among Indian patients, followed by Chinese and Malay. A modest bimodality in the age of psoriasis onset was observed among the groups aged 20-29 and 50-59 years. Psoriasis onset was significantly later in male than female patients and in Chinese vs. Indian and Malay patients., (© 2022 The Authors. British Journal of Dermatology published by John Wiley & Sons Ltd on behalf of British Association of Dermatologists.)