Risk factors of permanent hypoparathyroidism after total thyroidectomy and central neck dissection for papillary thyroid cancer: a prospective study

Introduction: Inadvertent removal of, or damage to the parathyroid glands in the course of operations on the anterior neck compartment are responsible for over 80% of cases of chronic hypoparathyroidism (HypoPT). This study searched for factors related to the development of permanent HypoPT after total thyroidectomy and central neck lymphadenectomy in patients with thyroid carcinoma. Material and methods: In total, 89 of 103 screened patients met the study's criteria and were put under prospective one-year observation. Demographic and surgical factors as well as the biochemical parameters of mineral homeostasis, controlled both preoperatively and postoperatively, were subject to statistical analysis. In line with contemporary guidelines, postoperative hypocalcaemia, rather than an abnormally low serum parathormone (PTH) concentration, was considered a diagnostic criterion of HypoPT. Results: On postoperative day one (POD1), serum concentration of PTH decreased below the normal range (< 12 pg/mL) in 29 patients and was undetectable in 19 patients (< 6 pg/mL). At one year postoperatively, 12 patients with undetectable POD1 PTH required treatment for hypocalcaemia and were diagnosed with permanent hypoPT. All the other patients regained normocalcaemia. Relative risk of permanent HypoPT associated with undetectable POD1 PTH was 88.75. A significant difference in median POD1 serum calcium concentration between the patients with undetectable POD1 PTH and those with detectable POD1 PTH was found (p < 0.001). The difference between the POD1 serum calcium in patients with permanent or transient HypoPT in the subgroup with undetectable POD1 PTH did not reach the level of statistical significance (median, 1.82 mmol/L vs. 1.96 mmol/L). At one month postoperatively, in patients who later developed permanent HypoPT, serum calcium was lower than it was in all other patients (p = 0.167). At one year postoperatively, serum concentration of PTH was in the normal range in 10 of 12 patients with permanent HypoPT; however, it was significantly lower than it had been before the operation and distinctly lower than it was in patients who regained normocalcaemia. The number of parathyroid glands either dissected or autotransplanted did not affect the development of permanent HypoPT. Conclusions: Undetectable POD1 PTH is an important risk factor of permanent HypoPT. The main cause of permanent HypoPT was irreversible damage to the left in situ parathyroid glands.