Twenty-year trend of thyrotoxicosis and thyrotoxic periodic paralysis: a population-based cohort study

Objective: Thyrotoxic periodic paralysis (TPP) is a rare but potentially lethal complication of thyrotoxicosis. Absence of large cohorts limits the conduct of epidemiology studies. We aimed to establish a population-based registry of thyrotoxicosis and TPP in Hong Kong and evaluate their trend. Methods: We developed algorithms to identify thyrotoxicosis and TPP cases from a representative electronic medical database in Hong Kong. Of the potential cases (thyrotoxicosis:83,184; TPP:999), we reviewed clinical notes and laboratory test records of 200 randomly selected cases. Population-based registries of thyrotoxicosis and TPP were subsequently established. Their standardized incidence rate, TPP-associated hospitalization rate, length of stay (LOS), and trends from 2002 to 2021 were evaluated. Results: Positive predictive values for thyrotoxicosis and TPP were 0.86-0.97, respectively, enabling establishment of population-based cohorts of incident thyrotoxicosis (n = 77,856) and TPP (n = 994). Age- and sex-standardized incidence rate (per 100,000 person-years) of thyrotoxicosis increased from 41.31 in 2002 to 69.51 in 2021 (average annual percentage change: 4.77%), with a similar trend observed in both sexes. TPP patients were predominantly male (93.66%). In 2002 and 2021, the age-standardized incidence rate (per 100,000 person-years) of TPP in males was 1.43 and 1.18, respectively, while that in females was 0.11 and 0.13, without a significant trend observed. TPP-associated hospitalization rate (90.91-100%) and median LOS (2-3 days) were steady across the two decades. Conclusion: This is the first study establishing a TPP cohort based on validated clinical data from an electronic medical database. It is important to keep monitoring the increasing incidence rate of thyrotoxicosis.