Purpose: 25-OH D3 (D3) deficiency causes secondary hyperparathyroidism. Asymmetric gland hypertrophy may also lead to unnecessary parathyroid gland resection by mistaking these glands for parathyroid incidentalomas. We tested the hypothesis that D3 deficiency causes parathyroid gland hypertrophy.
Method: This is a prospective study of 100 consecutive patients undergoing total thyroidectomy. Pre-operative D3 measurement was made at first presentation and on the day after surgery. During thyroidectomy, the parathyroid glands were searched for and measured. Using an ellipsoid volume calculator, the gland volume was calculated. This was correlated with D3 and other possible confounding factors.
Results: Normal parathyroid volume is 25.1 mm(3). Parathyroid gland size correlated with D3 levels, p < 0.001. There is a greater asymmetry in gland volume in those patients with the lowest levels of D3 (Spearman's rank correlation coefficient r = -0.51). There was a significant difference in individual gland volume between D3 levels >30 ng/ml and those <30 ng/ml. However, there was no difference in mean gland volume between these groups. There was no difference in correlation according to pathology or thyroid specimen weight.
Conclusion: There is a significant difference in both individual gland volume and variation in parathyroid gland volume according to D3 levels. Patients with a D3 level <30 ng/ml have a more asymmetrical hyperplasia corresponding with parathyroid incidentalomas. D3 levels should be measured pre-operatively in all patients undergoing total thyroidectomy to avoid unnecessary parathyroid resection.