Effect of 131I 'clear residual thyroid tissue' after surgery on the function of parathyroid gland in differentiated thyroid cancer

The Effects of Radioiodine Therapy on the Recovery of Parathyroid Function in Patients with Protracted Hypoparathyroidism after Total Thyroidectomy for Papillary Thyroid Carcinoma

BACKGROUND

To determine the effect of 131I treatment on postoperative parathyroid function and the timing of recovery of parathyroid function (RPF) in patients with protracted hypoPT.

METHODS

260 patients with papillary thyroid cancer (PTC) were retrospectively analyzed, including 166 patients treated with radioactive iodine-131 (131I) classified into the 131I group and 94 patients without 131I treatment classified into the control group. Data on clinicopathological characteristics, demographics, dose and interval time of 131I treatment, number of parathyroid glands remaining in situ (PGRIS), occurrence of hypoPT, duration of RPF, preoperative and postoperative levels of Ca and PTH were collected.

RESULTS

The patients in the 131I group showed a higher persistent hypoPT rate than those in the control group (p = 0). The PGRIS and total number of PG were significantly higher in patients who recovered from protracted HypoPT (p = 0.02; p = 0.03). PGRIS and 131I treatment [1 ∼ 2 VS 0, p = 0.03, OR 3.19; 3 ∼ 4 VS 0, p = 0.02, OR3.62; p = 0.02, OR 1.98, respectively] were independent factors influencing postoperative persistent hypoPT. The timing of RPF differed significantly for patients in the control group compared to those in the 131I group [p = 0.00].

CONCLUSIONS

We found that 131I treatment significantly prolonged the RPF of patients with protracted hypoPT and caused late RPF (even beyond 12 months). The diagnosis of "permanent" hypoPT should be cautiously made at least 12 months after surgery, especially in patients who receive 131I treatment.

Parathyroid Hormone Level Changes Following Radioiodine Therapy for Thyroid Cancer: A Prospective Observational Study

OBJECTIVE

Our objective was to analyze the effect of radioiodine (RAI) therapy on parathyroid hormone (PTH) secretion.

METHODS

A total of 137 patients were included and divided into 2 groups based on pretherapy PTH levels. The residual thyroid tissue volume was classified into 4 grades (0-3), and a value of 0 indicated that there was no apparent residual tissue. We analyzed the PTH level changes among different time points in each group and the factors that could predict the PTH level changes.

RESULTS

In 113 patients with normal parathyroid gland function, the PTH level at baseline, 1 day, 7 days, 1 month, 3 months, and 6 months after RAI therapy did not show any significant difference; in 24 patients with decreased parathyroid gland function, the level of PTH immediately decreased after the implementation of RAI therapy but gradually returned to a pre-RAI therapy level within 6 months. On the seventh day after therapy, the mean value of PTH in patients with a residual thyroid tissue volume of extent of 0/1 was 8.0 ± 2.3 pg/mL, which was significantly higher than that in patients with a residual thyroid tissue volume of extent of 2/3 (P = .011). Similar phenomena were observed 1 month, 3 months, and 6 months after therapy.

CONCLUSION

RAI therapy had a significant transient adverse effect on parathyroid gland function in patients with decreased PTH secretion pretherapy, and the extent was associated with the amount of residual thyroid tissue.

Parathyroid Changes After RAI in Patients With Differentiated Thyroid Carcinoma

OBJECTIVE

The purpose of this study was to investigate parathyroid hormone (PTH), serum calcium, phosphorus, and 25-hydroxyvitamin D (25-OH-VD) changes before and after radioactive iodine (RAI) in differentiated thyroid carcinoma (DTC) patients at different time points.

METHODS

A total of 259 DTC patients who received RAI were prospectively enrolled. We evaluated PTH, serum calcium, phosphorus, and 25-OH-VD levels at baseline pre-RAI, five days, six weeks, and six months post-RAI, respectively. We analyzed the risk factors of hypocalcemia at five days post-RAI.

RESULTS

The mean PTH, serum calcium and phosphorus values decreased five days post-RAI compared with pre-RAI (PTH 4.18 ± 1.23 pmol/L vs. 3.95 ± 1.41 pmol/L; calcium 2.27 ± 0.09 mmol/L vs. 2.20 ± 0.11 mmol/L; phosphorus 1.25 ± 0.17 vs. 0.98 ± 0.20 mmol/L, P < 0.05), and the differences were statistically significant. The mean 25-OH-VD levels did not significantly decrease at five days post-RAI. 21.2% (55/259) of patients had hypocalcemia at five days post-RAI, and all of them were given oral calcium supplements. At six weeks post-RAI, all of the above parameters were higher than those at five days post-RAI. Multivariate regression analysis showed that baseline pre-RAI serum calcium < 2.27 mmol/L, PTH < 4.18 pmol/L and negative ^99mTcO₄^- thyroid imaging were risk factors for hypocalcemia at five days post-RAI.

CONCLUSION

For DTC patients with normal PTH and serum calcium levels at pre-RAI, their PTH, serum calcium, and phosphorus levels decreased at five days post-RAI. About one-fifth of patients could have hypocalcemia at five days post-RAI. Lower baseline pre-RAI serum calcium and PTH levels and negative ^99mTcO₄^- thyroid imaging were risk factors for hypocalcemia five days post-RAI.

The effects of radioiodine therapy on parathyroid function among patients with papillary thyroid cancer: a retrospective cohort study

PURPOSE

To explore the effects of initial radioiodine therapy on parathyroid function among postoperative papillary thyroid cancer (PTC) patients.

METHODS

Postoperative PTC patients who were admitted in our department from April 2018 to April 2019 were recruited. Patients were divided into two groups: Group A, who underwent surgery and initial radioiodine therapy in our hospital, and Group B, who did not receive radioiodine therapy after surgery. The levels of serum calcium, magnesium, phosphorus, parathyroid hormone (PTH), and 25 hydroxyvitamin D3 were collected. Data were analyzed by SPSS 25.0.

RESULTS

A total of 252 patients were included. Between the two groups, no significant difference of PTH in 6th, 9th, and 12th month was found during postoperative follow-up (p = 0.493, p = 0.202, p = 0.814). No significant difference of PTH was found after stratifying Group A according to ¹³¹I dosage (p = 0.751 for 6th month after operation, p = 0.130 for 9th month after operation, p = 0.683 for 12th month after operation), interval time between surgery and radioiodine therapy (p = 0.522 for 3rd day after ¹³¹I therapy, p = 0.184 for 9th month after operation, p = 0.311 for 12th month after operation), and ratio of parathyroid autotransplantation (p = 0.545 for 3rd day after ¹³¹I therapy, p = 0.485 for 6th month after operation, p = 0.201 for 9th month after operation, p = 0.146 for 12th month after operation).

CONCLUSIONS

Initial radioiodine therapy following PTC surgery had no significant adverse effect on parathyroid function in the short term. However, physicians should inform patients of possible risks of abnormal parathyroid function prior to RAI therapy, and parathyroid function was periodically reviewed after RAI therapy.