Clinical aspects of early and late hypocalcaemia afterthyroid surgery

This study aimed to evaluate hypocalcaemia (time-course) and need for calcium administration after thyroid surgery in 135 consecutive cases (69 bilateral subtotal thyroidectomies, 50 unilateral lobectomies, 13 total thyroidectomies and three isthmectomies) for benign lesions and for differentiated carcinoma in 89% and 11% respectively.

In unilateral lobectomy, two parathyroid glands were identified and preserved in 72%, and one gland in 28% of the patients; calcaemia decreased by 10% on average in the early post-operative period (P<0.001). Calcium treatment (average: 2.3 days) was administered to 34% of the patients, these patients had lower nadir post-operative calcaemia than those who did not receive calcium: 2.03 vs 2.14 mmol/l (P<0.001). Their calcaemias reverted to normal within 1 week after surgery and remained normal thereafter without further calcium administration. In bilateral procedures, four parathyroid glands were preserved in 40%, three in 42%, two in 16%, and only one in 2% of the cases. Calcaemia decreased by 15% on average (P<0.001), and early hypocalcaemia was common and severe in some patients: nadir post-operative calcaemia <2.0 mmol/l in 61%, and <1.75 mmol/l in 6% of the cases. Post-operative hypocalcaemia was more pronounced after total than subtotal thyroidectomy (1.86+/-0.19 vs 1.98+/-0.14 mmol/l P=0.014), and also after lymph node dissection (1.83+/-0.11 mmol/l). Serum parathormone (PTH) decreased from 36 ng/l before surgery to 17 ng/l in the week thereafter (P=0.001). There was a linear relationship between the number of preserved parathyroid glands and early hypocalcaemia. The percentage of patients requiring calcium treatment was: 24 h (15%), 2-7 days (26%), 8-180 days (33%), >1 year (9%).

The number of parathyroid glands preserved in situ did not help predict the duration of post-surgical calcium treatment, nor the final outcome of hypocalcaemia. However, when total calcium levels were compared in patients having had one or two glands preserved vs three or four parathyroid glands, it was possible to show that despite prolonged calcium administration, late calcaemias remained significantly lower during the first 6 months in patients with a smaller number of parathyroid glands. Hypoparathyroidism, defined functionally on the basis of requirement of calcium supplementation 1 year after surgery, occurred in 8.6% of patients after bilateral lobectomy (despite measurable but inappropriately low-PTH concentration). This outcome could have been predicted earlier (after 3 to 6 months) and the patients perhaps given the benefit of definitive vitamin D treatment earlier, in order to avoid late and prolonged hypocalcaemia. Evaluation after 1 year showed that only one patient out of 82 bilateral lobectomies (1.2%) had permanent hypoparathyroidism and needed calcium whereas hypocalcaemia was persistent in one out of four patients who had undergone a staged procedure (i.e. heterolateral lobectomy years after a previous operation).