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.