We assessed thyroid function for 12 months after subtotal thyroidectomy in 100 tyrotoxic patients treated with propranolol alone before and immediately after operation. The operation proved safe, with low morbidity. Suppression of the hypothalamic-pituitary-thyroid axis, present in the majority one month after operation, was evidenced by normal or low levels of serum total tri-iodothyronine and thyroxine, but absent or subnormal serum thyrotropin response to thyrotropin-releasing hormone. Eighty patients were euthyroid at 12 months. Three patterns of thyroid function were observed in this group between the first and 12th months: normal serum total tri-iodothyronine, thyroxine and thyrotropin levels at all stages (20 patients); normal serum total tri-iodothyronine and thyroxine, but raised thyrotropin levels on one or more occasions (40 patients); and temporary hypothyroidism (20 patients). Of the remaining 20 patients, permanent hypothyroidism developed in 14, and six relapsed. Postoperative thyroid function was related to the estimated weight of the thyroid remnant.

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Plasma calcitonin, parathyroid hormone, total thyroid hormones and calcium were measured in 6 patients before, during and after thyroidectomy for hyperthyroidism. In 4 patients, plasma calcium fell postoperatively by 0.23--0.46 mmol/l, but there was no change in calcitonin or parathyroid hormone levels. In one patient, in whom there was a postoperative fall in plasma calcium of 0.55 mmol/l, thyroid hormones rose to a peak at 1 h and calcitonin to a peak at 12 h after resection. However, the rise in calcitonin occurred 8 h after the initial decrease in plasma calcium. In this patient, parathyroid hormone levels showed a slight rise only. It is concluded that, while thyroid hormones and calcitonin may leak from the damaged thyroid remnant after surgery, it is unlikely that calcitonin is important in the production of postoperative hypocalcaemia. However, impaired parathyroid hormone secretion may be a contributing factor.

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