Explaining the Variation in Surgical Practice for Differentiated Thyroid Cancer in Ontario, Canada.

IMPORTANCE In the management of differentiated thyroid cancer (DTC), the extent of surgical treatment required for most patients remains controversial and varies widely. This variation may be associated with the Enthusiasm Hypothesis, the notion that geographic differences in use of health care services are driven by the prevalence of physicians with a preference for particular services. OBJECTIVE To evaluate the Enthusiasm Hypothesis and its applicability to the variation in the surgical treatment of thyroid cancer in Ontario, Canada. DESIGN, SETTING, AND PARTICIPANTS This population-based study obtained electronic data on all health care-associated events for the complete population of insured residents of Ontario, Canada. Patients (n=28754) who were 18 years of age or older and underwent an initial therapeutic thyroid surgical procedure for a papillary or follicular carcinoma diagnosis between January 1, 2000, and December 31, 2015, were included. The final data analysis was performed January 31, 2019. EXPOSURES Therapeutic thyroid cancer surgical procedure. MAIN OUTCOMES AND MEASURES Numbers of surgeons, extent of surgical treatment, and case volumes in 14 geographic regions in Ontario. RESULTS In total, 28754 patients with DTC were included, of whom 22 600 (78.6%) were female, with a mean (SD) age of 49 (14) years. The use of total thyroidectomy for DTC varied widely across geographic regions of Ontario, from 45.8% to 77.1% of all cancer cases. More than 90% of the overall variation in practice (total thyroidectomy vs less-than-total thyroidectomy) could be explained by the practices of the high-volume surgeons (enthusiasts) in regions with the highest rates of thyroid cancer diagnosis. CONCLUSIONS AND RELEVANCE The Enthusiasm Hypothesis appears to be consistent with the findings of this study. The practices of the high-volume surgeons who were enthusiastic for total thyroidectomy in the geographic regions with the highest rates of thyroid cancer diagnosis may account for the variation in practice across Ontario between 2000 and 2015.