Late remission and “late onset” of hypoparathyroidism after total and completion thyroidectomy: a retrospective cohort study of 1060 patients from a tertiary referral center

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PURPOSE: This single-center retrospective study investigates the incidence of hypoparathyroidism after bilateral thyroidectomy at a tertiary referral center over one decade, including risk factors, time to recovery, and reasons for belated treatment initiation in seemingly "late onset" hypoparathyroidism. METHODS: Patients who underwent total/completion thyroidectomy from January 2011 to December 2020 were included. Potential risk factors for hypoparathyroidism were retrieved from the medical records. Hypoparathyroidism was defined as treatment with an activated vitamin D analogue (AVDA). The incidence was registered 0, 6, 12, and >12 months postoperatively. Hospital records were cross-linked with the national prescription database to ensure complete follow-up. RESULTS: The incidence of hypoparathyroidism increased from 10.1% upon hospital discharge to 11.4% after 6 months, 12.2% after 12 months, and 12.6% >12 months (median follow-up 7.7 years). The cumulative recovery rate was 19.9% by 6 months, 23.6% by 12 months, and 29.8% >12 months. As many as 23.3% of patients with persistent hypoparathyroidism did not start AVDA treatment within 6 months of surgery, and 12.0% started treatment beyond one year after surgery. In contrast, 9.3% of patients receiving AVDA by 12 months went into remission later on. Two variables emerged as independent risk factors for persistent hypoparathyroidism: re-operation for bleeding (OR 4.21; 95%CI 1.31-13.38) and surgery due to a diagnosis/suspicion of thyroid cancer (OR 2.09; 95%CI 1.04-4.19). CONCLUSION: The incidence of postoperative hypoparathyroidism is high and calls for action. Importantly, reassessment of post-surgical parathyroid function should be done regularly in order to neither overlook "late onset" hypoparathyroidism, nor late remission.