Beyond Surgical Follow-Up: Measuring the Long-Term Burden of Permanent Hypoparathyroidism After Thyroid Cancer Surgery

Background: Permanent postoperative hypoparathyroidism (p-HypoPT) is a major long-term complication of thyroid surgery; however, its incidence remains uncertain because reported rates are influenced by heterogeneous case mix and variable follow-up. We assessed the burden and determinants of p-HypoPT in patients undergoing surgery for differentiated thyroid cancer (DTC) with long-term endocrine follow-up. Methods: We retrospectively analysed prospectively collected data from 518 consecutive adults with DTC enrolled in a dedicated longitudinal endocrine follow-up programme between 2013 and 2022. p-HypoPT was operationally defined as the persistent requirement for oral calcium and/or active vitamin D supplementation at ≥12 months after surgery. Independent associations were assessed by means of multivariable logistic regression. Rates were also explored across the 2015 and 2025 American Thyroid Association (ATA) risk categories. Results: p-HypoPT occurred in 60/518 patients (11.6%). Median follow-up was 10.8 years (IQR 8.0–12.8), and all patients with p-HypoPT remained on calcium and/or active vitamin D supplementation at their latest available follow-up. Central neck dissection was associated with p-HypoPT in multivariable analysis (adjusted OR 2.94, 95% CI 1.55–5.57; p < 0.001). Under the 2025 ATA classification, p-HypoPT frequencies differed across categories in unadjusted analysis (p = 0.005), with the highest frequency in the high-intermediate-risk group (23.9%). This association was attenuated after adjustment for central and lateral neck dissection and was no longer statistically significant (global p = 0.566). Conclusions: Permanent hypoparathyroidism represents a relevant long-term burden after DTC surgery. Its assessment should account for both the duration of postoperative surveillance and the extent of surgery, moving beyond aggregate rates derived from heterogeneous thyroidectomy cohorts. More granular, procedure-specific and risk-adjusted estimates may ultimately support meaningful quality comparisons and provide a more individualised assessment of long-term functional risk.