Endocrine Abstracts

Background: Thyrotoxic periodic paralysis (TPP) is a rare complication of thyrotoxicosis, characterized by recurrent hypokalemia, episodic muscle weakness and paralysis. It is potentially fatal in serious attacks with occurrence of life-threatening cardiopulmonary complications. Currently, lack of large cohorts comprising individuals with TPP history restrict the conduct of relevant epidemiology study.

Methods: Clinical data from a population-wide electronic medical database in Hong Kong, namely the Clinical Data Analysis and Reporting System (CDARS), was retrieved for the study. The diagnostic coding and/or potassium test records in blood were used to randomly identify 100 potential cases of thyrotoxicosis [by International Classification of Diseases, 9^th Revision, Clinical Modification (ICD-9-CM): 242.××] and TPP (by ICD-9-CM: 242.×× and 359.3, plus low potassium level) for validation, respectively. The positive predictive value (PPV) of the clinical data from CDARS for thyrotoxicosis and TPP were determined by reviewing clinical notes and examining relevant laboratory test records. A population-based registry of thyrotoxicosis and TPP in Hong Kong was subsequently established. With reference to the United Nations population, we computed the standardized incidence rate of both thyrotoxicosis and TPP in Hong Kong, with average annual percentage change (AAPC) for trend analysis.

Findings: The PPV of clinical data in CDARS for thyrotoxicosis and TPP were 86% [95% Confidence Interval (CI): 79.2%-92.8%] and 98% (95% CI: 95.3%-100%), respectively. With this high PPV, we established a populational-based cohort, comprising 83,185 and 971 adults with diagnosis of thyrotoxicosis and TPP respectively from 1 January 2002 to 31 December 2021. The proportion of thyrotoxicosis patients experiencing TPP was 1.17%. The age- and sex-standardized incidence rate of thyrotoxicosis increased from 50.031 to 76.516 per 100,000 person-years from 2002 to 2021, with AAPC of 4.6 (95% CI: 1.11-8.01). Such increasing trend was also observed in male and female. Since more male thyrotoxicosis patients had TPP with reference to female patients, the age-standardized incidence rate of TPP in both sexes were calculated. In 2002 and 2021, the incidence rate in male was 1.405 and 1.226 per 100,000 person-years respectively. Whereas the incidence rate in female was 0.097 and 0.131 per 100,000 person-years. No significant trend was observed in both sexes.

Interpretation: This is the first study validating the clinical data in electronic medical database for TPP. The high PPV of validation enabled us to establish the largest population-based cohort of individuals with TPP history to-date, facilitating future epidemiology studies of this rare complication.