Thyrotoxicosis in an Indigenous New Zealand Population – a Prospective Observational Study

BACKGROUND: Reported international incidence rates of thyrotoxicosis vary markedly, ranging from 6 to 93 cases per 100 000 per annum. Along with population demographics, exposures, and study design factors, ethnicity is increasingly being recognized as a potential factor influencing incidence. This study aimed to document the epidemiology and clinical presentation of thyrotoxicosis for Māori, the indigenous population in New Zealand. METHODS: A prospective study of adult patients presenting with a first diagnosis of thyrotoxicosis between January 2013 and October 2014 to a single New Zealand center. Demographic data were collected, and detailed clinical assessment performed. RESULTS: With 375 patients, an incidence rate of thyrotoxicosis of 73.0 per 100 000 per annum was identified. Of these, 353 (94.1%) participated in the study. The median age of the cohort was 47 years, 81% were female, and 58% had Graves disease. The overall incidence of thyrotoxicosis for Māori, the indigenous people of New Zealand, was higher than non-Māori (123.9 vs 57.3 per 100 000 per annum). Rates of both Graves disease and toxic multinodular goiter were higher in Māori as compared to non-Māori (incidence rate ratios of 1.9 [1.4, 2.6] and 5.3 [3.4, 8.3], respectively), with this increase being maintained after controlling for age, deprivation, and smoking. CONCLUSIONS: Māori, the indigenous people of New Zealand, have an increased incidence of thyrotoxicosis compared to non-Māori and, in particular, toxic multinodular goiter. A greater understanding of the epidemiology of thyrotoxicosis in other indigenous and marginalized ethnic groups may help to optimize therapeutic pathways, equitable care and outcomes.