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

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.

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.

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.

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.