Background: The predictors of intra-operative PTH (IOPTH) decline during minimally invasive parathyroidectomy (MIP) for primary hyperparathyroidism have been but poorly studied.
Materials and methods: This retrospective study included 108 patients who underwent MIP for a single adenoma. Serum calcium and phosphorus were measured before surgery and 1 day post-operatively. IOPTH was measured before (intra-operative preincision or PTHt0) and 10 min after removal of the adenoma (PTHt10). The Modification of Diet in Renal Disease (MDRD) equation was used to estimate the glomerular filtration rate. The weight of the adenoma was assessed in all the subjects.
Results: The sex ratio female/male was 5.37 with a mean age of 57.3 yr. The mean pre- and postoperative values were for calcium 2.80 and 2.19 mmol/l, respectively (p<0.0001) and for phosphorus 0.90 and 1.16 mmol/l, respectively (p<0.0001). The PTH dropped from a mean value of 184.8 to 50.8 pg/ml 10 min after adenoma resection with a mean drop of 69.7%. Thirteen patients (12%) did not achieve a PTH fall of more than 50%. In a bivariate analysis, age, an MDRD<60 ml/min and weight of adenoma were inversely associated with IOPTH fall (p=0.009, p=0.004, and p<0.001, respectively) while gender, body mass index, hypertension, diabetes, pre-operative phosphorus and calcium had no significant effects. In the multivariate analysis, age, weight of adenoma, and MDRD were still independent negative predictors of the IOPTH fall (p=0.01, p=0.018, and p<0.001, respectively).
Conclusion: Our results suggest that during MIP the presence of a parathyroid adenoma with a high weight, in an elderly subject or in a subject with altered renal function, will result in a lesser degree of IOPTH fall.