Clinical aspects of early and late hypocalcaemia after thyroid surgery

Aim: This study aimed to evaluate hypocalcaemia (time-course) and need for calcium administration after thyroid surgery in 135 consecutive cases (69 b ilateral subtotal thyroidectomies, 50 unilateral lobectomies, 13 total thyr oidectomies and three isthmectomies) for benign lesions and for differentia ted carcinoma in 89% and 11% respectively. Results: In unilateral lobectomy, two parathyroid glands were identified an d preserved in 72%, and one gland in 28% of the patients; calcaemia decreas ed 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, thes e 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 t o normal within 1 week after surgery and remained normal thereafter without further calcium administration. In bilateral procedures, four parathyroid glands were preserved in 400%, th ree in 42%, two in 16%, and only one in 2% of the cases. Calcaemia decrease d by 15% on average (P<0.001), and early hypocalcaemia was common and sever e 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 pron ounced after total than subtotal thyroidectomy (1.86+/-0.19 vs 1.98 +/- 0.1 4 mmol/l; P = 0.014), and also after lymph node dissection (1.83 +/- 0.11 m mol/l). Serum parathormone (PTH) decreased from 36 ng/l before surgery to 1 7 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%). Discussion: The number of parathyroid glands preserved in situ did not help predict the duration of post-surgical calcium treatment, nor the final out come of hypocalcaemia. However, when total calcium levels were compared in patients having had one or two glands preserved vs three or four parathyroi d glands, it was possible to show that despite prolonged calcium administra tion, late calcaemias remained significantly lower during the first 6 month s in patients with a smaller number of parathyroid glands. Hypoparathyroidism, defined functionally on the basis of requirement of cal cium supplementation 1 year after surgery, occurred in 8.6% of patients aft er bilateral lobectomy (despite measurable but inappropriately low-PTH conc entration). This outcome could have been predicted earlier (after 3 to 6 mo nths) and the patients perhaps given the benefit of definitive vitamin D tr eatment earlier, in order to avoid late and prolonged hypocalcaemia. Evalua tion after 1 year showed that only one patient out of 82 bilateral lobectom ies (1.2%) had permanent hypoparathyroidism and needed calcium whereas hypo calcaemia was persistent in one out of four patients who had undergone a st aged procedure (i.e. heterolateral lobectomy years after a previous operati on). (C) 2000 Harcourt Publishers Ltd.