Is hungry bone syndrome a cause of postoperative hypocalcemia after total thyroidectomy in thyrotoxicosis? A prospective study with bone mineral density correlation.

BACKGROUND: Hungry bone syndrome is a well-established cause of postoperative hypocalcemia in thyrotoxicosis. To date, the incidence of hungry bone syndrome after total thyroidectomy is unclear. This prospective study examined the incidence of postthyroidectomy hungry bone syndrome and its correlation with preoperative bone mineral density.

METHODS: Forty thyrotoxic subjects (Group A; age: mean ± SD; 36.5 ± 9.8 years) and 40 euthyroid controls with benign thyroid nodules (Group B) undergoing total thyroidectomy were evaluated for preoperative bone mineral density and serum calcium, magnesium, phosphorus, parathyroid hormone, alkaline phosphatase, and 25-Hydroxy Vitamin D serially. At least 3 parathyroid glands were preserved.

RESULTS: Both groups were age and sex matched. Thyrotoxic subjects had higher postoperative hypocalcemia (82.5% vs controls 22.5%, 95% confidence interval 37.9 to 75.4), low preoperative bone mineral density and raised alkaline phosphatase (each, P = .001). Among thyrotoxic subjects experiencing hypocalcemia (n = 33), 39.4% (13/33) exhibited hungry bone syndrome (characterized by simultaneous fall in serum calcium, magnesium, and phosphorus), 18.1% (6/33) had hypoparathyroidism and 12% had hypomagnesemia. Hypocalcemic subjects exhibiting hungry bone syndrome displayed further decreased preoperative bone mineral density in the spine (0.875 ± 0.138 vs 1.024 ± 0.149 g/cm2 , P = .004) and low serum magnesium 72-hour postsurgery (0.57 ± 0.23 vs 0.88 ± 0.25 mmol/L, P = .013) than those not exhibiting hungry bone syndrome. Postoperative serum calcium correlated with preoperative bone mineral density in the spine (P = .013). In group B subjects experiencing hypocalcemia (n = 9), none exhibited hungry bone syndrome but 77.78% (7/9) had hypoparathyroidism. All but one was eucalcemic after 6 months.

CONCLUSION: Hungry bone syndrome occurs exclusively in thyrotoxic subjects and constitutes the major cause of postoperative hypocalcemia after total thyroidectomy. Vertebral osteoporosis and hypomagnesemia within 72 hours after total thyroidectomy is associated with the risk of hungry bone syndrome.