Perioperative kinetics of parathyroid hormone in unilateral, primary thyroid surgery

Activation of the Calcium-Sensing Receptor by a Subfraction of Amino Acids Contained in Thyroid Drainage Fluid

Hypoparathyroidism is a common sequela of thyroid surgery; in this study, we aimed at exploring the pathogenesis behind it. The following premises suggest that wound fluid might be a causative agent. (i) Parathyroid hormone secretion is under feedback control by the calcium-sensing receptor, which responds to a diverse array of activating ligands. (ii) Postoperative hypoparathyroidism arises from a secretory deficiency of the parathyroid glands. Even in patients later unaffected by hypoparathyroidism, parathyroid hormone levels drop within hours after surgery. (iii) Wound fluid is bound to enter the tissue around the thyroid bed, where the parathyroid glands are located. Its composition is shaped by a series of proteolytic reactions triggered by wounding. Using thyroid drainage as a surrogate, we addressed the possibility that wound fluid contains compounds activating the calcium-sensing receptor. Drainage fluid ultrafiltrate was found to be rich in amino acids, and on separation by HPLC, compounds activating the calcium-sensing receptor partitioned with hydrophilic matter that rendered buffer acidic. The data show that glutamate and aspartate at millimolar concentrations supported activation of the calcium-sensing receptor, an effect contingent on low pH. In the presence of glutamate/aspartate, protons activated the calcium-sensing receptor with a pH50 of 6.1, and at pH 5, produced maximal activation. This synergistic mode of action was exclusive; glutamine/asparagine did not substitute for the acidic amino acids, nor did Ca2+ substitute for protons. NPS-2143, a negative allosteric receptor modulator completely blocked receptor activation by glutamate/aspartate and by fractionated drainage fluid. Thus, wound fluid may be involved in suppressing parathyroid hormone secretion.

Relationship of Vitamin D Deficiency and Intraoperative Parathyroid Hormone Elevation in Completion and Total Thyroidectomy

Objective

To quantify how frequently intraoperative parathyroid hormone levels increase during thyroid surgery and to explore a possible relationship between secondary hyperparathyroidism due to vitamin D deficiency and elevation in intraoperative parathyroid hormone.

Study Design

Case series with chart review.

Setting

Tertiary academic center.

Subjects and Methods

A total of 428 consecutive patients undergoing completion and total thyroidectomy by the senior author over a 7-year period were included for analysis. All patients had baseline and postexcision intraoperative parathyroid hormone levels as well as vitamin D levels from the same laboratory. Institute of Medicine criteria were employed for vitamin D stratification (>30, normal; 20-29.9, insufficient; <20, deficient) . Other data analyzed include sex, age, neck dissection status, and parathyroid autotransplantation.

Results

A total of 118 patients (27.6%) had an intraoperative parathyroid hormone elevation above baseline. Patients with vitamin D deficiency were significantly more likely to experience hormone elevation ( P = .04). When parathyroid hormone rose, it did so by a mean 32.1 pg/mL. Patients with vitamin D deficiency demonstrated significantly larger hormone increases ( P = .03).

Conclusion

Elevation in intraoperative parathyroid hormone levels above baseline after completion and total thyroidectomy occurs in over one-fourth of cases and is significantly associated with vitamin D deficiency. This study is the first to report this observation. We hypothesize that vitamin D deficiency in these patients may create a subclinical secondary hyperparathyroidism that leads to intraoperative parathyroid hormone elevation when the glands are manipulated. Additional studies will be needed to explore this physiologic mechanism and its clinical significance.

The timing of parathyroid hormone measurement defines the cut-off values to accurately predict postoperative hypocalcemia: a prospective study

PURPOSE

Serum intact parathyroid hormone (iPTH) level is an early marker of post-thyroidectomy hypocalcemia. However, lack of methodological standardization to define timing and cut-off points of iPTH measurement limit its clinical applicability. Here, we evaluated the relationship between two distinct postoperative time sampling and iPTH accuracy on predicting hypocalcemia.

METHODS

iPTH was measured within 4 h after surgery (iPTH 4 h) and on the morning of the first postoperative day (iPTH 1st PO). Hypocalcemia was defined by levels of total calcium corrected by serum albumin ≤ 8.0 mg/dL and/or by the presence of symptoms. The most accurate iPTH cut-off point for hypocalcemia prediction was established from a ROC curve comparing both time-points.

RESULTS

The study included 101 patients. The mean age was 52.4 ± 12.9 years, 93 were women (92.1%) and 69 patients underwent total thyroidectomy (68.3%). Hypocalcemia occurred in 25 patients (24.8%), of whom 12 were symptomatic. Total thyroidectomy, longer duration of surgery, surgical complications related to parathyroid glands and lower levels of iPTH 4 h and iPTH 1st PO were associated with postoperative hypocalcaemia (all P < 0.05). Using the ROC curve, the optimal cut-off points were 19.55 pg/mL and 14.35 pg/mL for iPTH 4 h and iPTH 1st PO, respectively. The comparison of the AUC showed no significant difference between these two points of evaluation (0.935 vs. 0.940; P = 0.415).

CONCLUSIONS

Serum iPTH levels measured within 4 h or on the first morning after surgery are predictors of postoperative hypocalcemia. Notably, both time-points have the same accuracy to predict postoperative hypocalcemia (with different cutoff points).

The Association of Discolored Parathyroid Glands and Hypoparathyroidism Following Total Thyroidectomy

BACKGROUND

It remains uncertain whether a parathyroid gland (PG) that appears darkened or severely bruised but still has an attached vascular pedicle should be left in situ or taken out and auto-transplanted following total thyroidectomy. Our study aimed to examine the impact of discolored PGs (DPGs) on short- and long-term hypoparathyroidism.

METHODS

One hundred and three patients who underwent total thyroidectomy with 4 clearly identified PGs were analyzed. Location (superior/inferior) and color of each PG were recorded. Patients without DPG were grouped into I while those with 1-2 DPGs and ≥3 DPGs were grouped into II and III, respectively. Transient hypoparathyroidism meant adjusted Ca <2.00 mol/L 24 h after surgery and/or need for supplements. Protracted hypoparathyroidism meant a subnormal PTH at 4-6 weeks and/or supplements >6 weeks. Permanent hypoparathyroidism meant supplements ≥1 year.

RESULTS

Relative to I, group III had greater adjusted Ca drop at postoperative 1-h (p = 0.012), 24-h (p < 0.001) and lower day-1 PTH (p = 0.015). Having ≥3 DPGs (OR 14.00, 95 % CI 1.575-124.474, p = 0.018) was an independent factor of transient hypoparathyroidism. However, permanent hypoparathyroidism rate was higher than in group I than II (p = 0.019). Eight patients (25.8 %) in group I had undetectable day-1 PTH, while none in group III had undetectable day-1 PTH. Graves' disease/toxic goiter (OR 15.166, 95 % CI 2.594-88.661, p = 0.003) and excised gland weight (OR 1.028, 95 % CI 1.010-1.046, p = 0.003) were independent factors of ≥3 DPGs.

CONCLUSIONS

PG discoloration is associated with transient hypoparathyroidism while normal colored PG with seemingly adequate blood supply does not always imply functionally normal gland. These findings highlights the need for a real-time intraoperative method to assess PG viability.

Single measurement of intact parathyroid hormone after thyroidectomy can predict transient and permanent hypoparathyroidism: a prospective study

OBJECTIVE

Immediate postoperative hypocalcemia is the most common complication of bilateral thyroidectomy. Although hypocalcemia is usually transient, it can be fatal. This study aimed to find a predictor of immediate postoperative hypocalcemia by using intact parathyroid hormone (PTH) level at 4 hours after thyroidectomy (iPTH4hr) compared with the decline in the percentage of intact PTH (%iPTH). We also followed the subjects for evaluation of permanent hypoparathyroidism.

METHODS

This was a prospective study of 65 patients (86.2% female, mean age: 43±15 years) who planned to undergo total or subtotal thyroidectomy. Preoperative and iPTH4hr were measured.

RESULTS

Thirty-nine patients (60%) were diagnosed with papillary thyroid carcinoma, while the rest were multinodular goiter (21.5%) and Graves' disease (7.7%). Significant immediate hypocalcemia was observed in 25 (38.5%) patients. Both iPTH4hr <12.5 pg/mL and %iPTH decline >72% could accurately predict significant immediate hypocalcemia. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for iPTH4hr were 92%, 87.5%, 82.1%, and 94.6%, respectively. The %iPTH decline was equal in accuracy, with sensitivity, specificity, PPV, and NPV of 84%, 90%, 84%, and 90%, respectively. At 6 months after surgery, 19 patients (29.2%) displayed permanent hypoparathyroidism. The iPTH4hr <12.5 pg/mL and %iPTH decline >72% could also predict permanent hypoparathyroidism, with sensitivity, specificity, PPV, and NPV of 100%, 80.4%, 67.9%, and 100%, and 94.7%, 84.8%, 72%, and 97.5%, respectively.

CONCLUSIONS

Only a single measurement of iPTH4hr could be helpful in identifying patients at risk of significant immediate hypocalcemia in need prompt treatment, and subsequently facilitating early discharge of patients. Also, this parameter can precisely predict permanent hypoparathyroidism.