Hemithyroidectomy: long-term effects on parathyroid function--preliminary report.

Early hypocalcemia after thyroid surgery has frequently been reported, whereas data regarding long-term effects on calcium homeostasis are scarce. We have previously studied patients after hemithyroidectomy with an oral calcium load test and found normal parathyroid hormone (PTH) suppression. However, the 1,25-dihydroxyvitamin D concentration was decreased and the phosphate concentration increased, implying parathyroid insufficiency. We therefore proceeded to investigate PTH secretion and suppression in 10 euthyroid patients subjected to hemithyroidectomy due to benign thyroid disease before and at 1 year after surgery. In addition, biochemical variables known to influence calcium homeostasis were analyzed. Basal, maximal, and total PTH secretion were unaltered 1 year postoperatively. However, maximal PTH secretion was reached at a lower serum level of ionized calcium, and there was a tendency toward increased parathyroid sensitivity to ionized calcium. Furthermore, compared to preoperative, total serum calcium, 1,25-dihydroxyvitamin D, and free thyroxine (T4) concentrations were decreased at follow-up. Total serum calcium and 1,25-dihydoxyvitamin D concentrations were decreased 1 year after hemithyroidectomy. These changes were not due to parathyroid insufficiency. Instead, our results imply increased parathyroid sensitivity to calcium and possibly reduced peripheral sensitivity to PTH.