Predicting hypoparathyroidism after thyroidectomy: the value of indocyanine green fluorescence angiography

Hypoparathyroidism is a worrying complication following thyroid surgery. Early recognition of patients at risk of developing postoperative hypoparathyroidism is of utmost importance in thyroid surgery. This study aimed to determine the risk factors that influence the preservation of parathyroid gland (PTG) vascular supply and their function after thyroidectomy and evaluate the value of indocyanine green fluorescence angiography (ICG-FA) in the prediction of the occurrence of postoperative hypoparathyroidism.

A prospective observational study was conducted on 87 patients undergoing total thyroidectomy. PTG vascularization was assessed using intraoperative ICG-FA. Demographic, histopathological and intraoperative data and biochemical values were collected. Two scores were proposed to access the accuracy of ICG-FA to predict postoperative hypoparathyroidism: total fluorescence score (sum of the scores of all recognized PTG during surgery) and mean fluorescence score (mean of the fluorescence scores of the recognized PTG). Biochemical hypoparathyroidism was defined as values of parathormone (PTH) <9 pg/dL, and temporary hypoparathyroidism was objectively evaluated. Statistical analysis was performed (P less than 0.05 was considered statistically significant).

There were 14 cases (16.1%) of postoperative hypoparathyroidism, all temporary. Demographic data, histopathological variables, preoperative biochemical values and number of recognized and autotransplanted PTGs didn't differ between patients with and without postoperative hypoparathyroidism. The PTG remaining in situ (PGRIS) score was significantly different (P=0.03). It was established a correlation between the location of the PTGs regarding the thyroid lobe and the intensity of ICG fluorescence after thyroid resection, especially in the inferior PTGs (P<0.001). It was verified that the two scores proposed in this study have high accuracy to predict postoperative hypoparathyroidism: total fluorescence score with a cut-off value of 4.5 [area under the curve (AUC) =0.667; 95% confidence interval (CI): 0.505-0.828; P=0.043] and mean fluorescence score with a cut-off value of 1.125 (AUC =0.652; 95% CI: 0.523-0.780; P=0.02).

The location of PTG regarding the thyroid lobe significantly affects the preservation of their vascularization and thus their function after total thyroidectomy. The ICG fluorescence-based scores proposed in this study are a helpful tool to predict postoperative hypoparathyroidism, especially the mean fluorescence score, that does not depend on the number of recognized PTG. The mean fluorescence score may take part of the management of patients after thyroidectomy by guiding the need to use calcium supplementation and time of hospital discharge.