Hypoparathyroidism and mortality after total thyroidectomy: A nationwide matched cohort study

Abstract Objective Total thyroidectomy (TT) carries a risk of hypoparathyroidism (hypoPT). Recently, hypoPT has been associated with higher overall mortality rates. We aimed to evaluate the frequency of hypoPT and mortality in patients undergoing TT in Denmark covering 20 years. Design Retrospective Cohort study. Patients and measurements Using population‐based registries, we identified all Danish individuals who had undergone TT between January 1998 and December 2017. We included a comparison cohort by randomly selecting 10 citizens for each patient, matched on sex and birth year. HypoPT was defined as treatment with active vitamin D after 12 months postoperatively. We used cumulative incidence to calculate risks and Cox regression to compare the rate of mortality between patients and the comparison cohort. We evaluated patients in different comorbidity groups using the Charlson Comorbidity Index and by different indications for surgery. Results 7912 patients underwent TT in the period. The prevalence of hypoPT in the study period was 16.6%, 12 months postoperatively. After adjusting for potential confounders the risk of death due to any causes (hazard ratio; 95% confidence intervals) following TT was significantly increased (1.34; 1.15‐1.56) for patients who developed hypoPT. However, subgroup analysis revealed mortality was only increased in malignancy cases (2.48; 1.99‐3.10) whereas mortality was not increased when surgery was due to benign indications such as goitre (0.88; 0.68‐1.15) or thyrotoxicosis (0.86; 0.57‐1.28). Conclusions The use of active vitamin D for hypoPT was prevalent one year after TT. Patients with hypoPT did not have an increased risk of mortality following TT unless the indication was due to malignancy.