Can preoperative vitamin D deficiency predict postoperative hypoparathyroidism following thyroid surgery?

Postoperative hypoparathyroidism remains a relevant problem after thyroid surgery. Although the roles of vitamin D deficiency and other risk factors have been discussed in previous studies, variable results have been reported. Predicting the risk of postoperative hypocalcemia could be helpful for individual prognoses and medical treatment. Documentation and analysis of bilateral thyroid operations performed between July 2011 and May 2014 were studied. Results involving age, gender, diagnosis, surgical techniques, pre- and postoperative calcium and parathyroid hormone (PTH) levels, and especially, the role of preoperative vitamin D levels were assessed in uni- and multivariate analyses. Bilateral thyroid surgery was performed in 361 patients with multinodular goiters (n = 224), Graves' disease (n = 40), or thyroid carcinoma (n = 97). In total, 124 patients (34%) with postoperative hypoparathyroidism, defined as having a PTH level ≤ 10 pg/mL, were treated with calcium and vitamin D regardless of their symptoms. The rate of permanent hypoparathyroidism was 3.6% and correlated with the extent of surgery; the highest risks were shown for total thyroidectomy and central lymph node dissection. In univariate analysis, the extent of surgery, parathyroid autotransplantation, and histopathology were the strongest predictors of hypoparathyroidism. Even severe vitamin D deficiency (< 10 ng/mL) showed a trend only towards a higher transient hypoparathyroidism risk (p = 0.0514) but failed to predict permanent hypoparathyroidism. Postoperative PTH levels accurately identified patients at risk for hypoparathyroidism. Decreased preoperative vitamin D levels could not predict hypocalcemia, and high vitamin D levels could not prevent permanent hypoparathyroidism.