Postoperative Parathyroid Hormone Levels Predict Hypoparathyroidism Risk

A meticulous surgical technique based on parathyroid autotransplantation, and not vitamin D supplementation, is more efficient to preserve parathyroid function and avoid postoperative hypoparathyroidism following thyroid surgery, a study shows.

The study, “Can preoperative vitamin D deficiency predict postoperative hypoparathyroidism following thyroid surgery?” was published in Langenbeck’s Archives of Surgery.

Hypoparathyroidism involves decreased secretion of parathyroid hormone, usually caused by damage to the thyroid glands, and can occur with and after thyroidectomy (surgery to remove the thyroid).

Even with meticulous dissection by surgeons, hypoparathyroidism is not always preventable. One way to restore parathyroid function and prevent permanent hypothyroidism is autotransplantation — transplantation of organs, tissues, or even particular proteins from one part of the body to another.

Restoring impaired parathyroid function is important, because deficiency results in low levels of vitamin D in the blood along with hypocalcemia — a condition in which there are lower-than-average levels of calcium in the blood. The short-term medical consequences of hypoparathyroidism include tingling, numbness, and muscle spasms.

Long-term hypocalcemia has serious health effects, including kidney impairment, cardiomyopathy — heart muscle disease — and calcification of the basal ganglia, which causes parkinsonism — problems controlling speech, movement, and posture.

To accurately predict postoperative parathyroid function, clinicians measure levels of the parathyroid hormone on the day after a thyroidectomy. If parathyroid hormone levels are too low (less than 10 pg/mL), the patient can be given calcium and vitamin D supplements to alleviate short-term symptoms of hypocalcemia. However, the influence of low vitamin D levels on postoperative hypocalcemia remain controversial among researchers.

“Until now, no study has demonstrated an impact of vitamin D levels on permanent hypocalcemia,” researchers said. “Because preoperative low vitamin D levels could be simply improved by vitamin D medication, the interaction between both parameters, preoperative vitamin D levels and postoperative hypoparathyroidism, should be thoroughly analyzed.”

For these reasons, researchers at Germany’s University Hospital Ulm and Catholic Hospital Mainz evaluated the influence of preoperative vitamin D levels on short-term and permanent postoperative hypoparathyroidism.

They examined a large series of patients who underwent bilateral thyroid surgery at these hospitals from July 2011 to May 2014. The researchers recorded preoperative vitamin D levels and postoperative hypocalcemia to understand whether preoperative vitamin D levels influence postoperative hypocalcemia in thyroidectomy or autotransplantation.

They also determined risk factors for each patient, and evaluated the participants for postoperative hypoparathyroidism.

A total of 361 hypoparathyroidism participants who underwent bilateral thyroid surgery were included in the study. Notably, 97 (26.9%) of these participants were treated for thyroid carcinoma. The remaining underwent surgery for multinodular goiters (62.6%) or Graves’ disease (10.5%).

These preoperative measurements were found in the participants:

• The average preoperative vitamin D levels were 20.2 ng/mL, far lower than the normal range of 30-60 ng/mL;
• Severe vitamin D deficiency, with levels below 10 ng/mL, was found in 84 of 361 patients;
• Only 21% of the patients had preoperative vitamin D levels within the normal range.

During surgery, parathyroid autotransplantation was performed in 162 of the 361 patients (44.9%). People have one to four parathyroid glands, two on each side. Most participants, about two out of three (68.7%), had at least three parathyroid glands.

These postoperative measurements were found in the participants:

• Overall, the rate of early postoperative hypoparathyroidism was about one in three (34.3%);
• Early postoperative hypoparathyroidism was not affected by the number of identified parathyroid glands (two to four) intraoperatively;
• Permanent hypoparathyroidism (lasting longer than six months) persisted in 13 patients (3.6%).

With these findings, the researchers observed only a minor, non-significant correlation between preoperative vitamin D levels of less than 10 ng/mL and early postoperative hypoparathyroidism (39.3%), and even less so in patients with hypoparathyroidism having vitamin D levels > 21 ng/mL (32.7%).

Instead, the strongest predictors of early postoperative hypoparathyroidism were being female, total versus near-total thyroidectomy, and parathyroid autotransplantation.

One of the strongest risk factors predicting permanent hypoparathyroidism was postoperative parathyroid hormone level. Twelve of 85 patients (14.1%) with no detectable parathyroid hormone levels at 24 hours post-thyroidectomy developed permanent hypoparathyroidism. On the other hand, among the subjects with early postoperative parathyroid hormone levels of at least ≥ 1 pg/mL, less than one percent of participants (0.4%) developed permanent hypoparathyroidism.

“According to our own data and recent publications, the hypothesis that preoperative vitamin D deficiency leads to a higher percentage of patients with post-thyroidectomy hypoparathyroidism remains contradictory,” researchers said.

“Based on these data, the idea of eliminating postoperative hypoparathyroidism with preoperative vitamin D supplementation will not likely be successful. The best way to preserve parathyroid function continues to be a meticulous surgical technique that more strictly indicates parathyroid autotransplantation.”

Finally, the researchers also found interesting links between thyroid cancer and hypoparathyroidism. The researchers observed a correlation between cancer stage and permanent hypoparathyroidism. Permanent hypoparathyroidism was detected more frequently in thyroid cancer patients with advanced tumor stages (2.2% stage 1, 4.5% stage 2, 8.0% stage 3, and 33.3% stage 4).

In total, 13.9% of patients with metastatic lymph nodes were treated for permanent hypoparathyroidism, compared to 2.6% of patients without lymph node metastases.