Calcium Metabolism in hyperthyroidism: impact of subtotal thyroidectomy

ABSTRACT

one of the most difficult situations confronting the clinician after thyroidectomy is the occurrence of tetany after an apparently perfect surgery where every effort had been made to preserve the parathyroid glands and their vasculature. The magnitude of the condition is extremely variable from one patient to another. to study calcium metabolism before and after thyroidectomy for hyperthyroidism in a trial to provide possible explanation for this problem. this is a prospective study in which serum calcium [total and ionized] and inorganic phosphorus, urinary calcium and phosphorus / creatinine ratios, intact parathyroid hormone and 1.25 [OH]2 vitamin D were measured pre- and one day, 3 days and 2 weeks post-operatively in 28 consecutive patients [26 females and 2 males] who underwent subtotal thyroidectomy for hyperthyroidism. the incidence of post-operative hypocalcaemia was 17.86% [5 out of 28 patients]. Three patients developed tetany about 3 days post-operatively and went back to normal within 10 and 13 days after calcium and vitamin D supplementation. Statistical analysis demonstrated that pre-operative serum parathyroid hormone levels were negatively correlated with ionized calcium levels and positively correlated with 1.25[OH]2 vitamin D. One day post-operatively, there was a statistical significant decrease in levels of ionized calcium and parathyroid hormone [P = 0.007 and 0.011 respectively]. Serum intact parathyroid hormone become positively correlated with serum ionized calcium at one day and 3 days post-operatively. Patients who developed hypocalcaemia showed ionized calcium levels less than or equal to 1.19 mmol/L and parathyroid hormone levels less than or equal to 2.63 pmol/L one day post-thyroidectomy, reaching 1.15 mmol/L or less and 1.26 pmol/L or less respectively 3 days post-operatively. Pre-operative significant lower serum ionized calcium, higher parathyroid hormone and higher 1.25[OH]2 vitamin D levels were observed in the hypocalcaemic patients in comparison to other patients who did not develop post-operative hypocalcaemia. pre-operative and one-day post-operative values of ionized calcium and parathyroid hormone and pre-operative 1.25[OH]2 vitamin D can help to predict patients who are at highest risk for post-operative hypocalcaemia after surgery for hyperthyroidism. Calcium and vitamin D supplementation can be recommended before and / or after thyroidectomy for those patients