Undetectable PTH in Blood May Be Risk Factor for Permanent Hypoparathyroidism Following Neck Surgery

Undetectable parathyroid hormone (PTH) levels in the blood one day after total thyroidectomy and removal of lymph nodes in the neck is a significant risk factor to develop permanent hypoparathyroidism, researchers suggest.

The study, “Risk factors of permanent hypoparathyroidism after total thyroidectomy and central neck dissection for papillary thyroid cancer: A prospective study,” was published in Endokrynologia Polska.

More than 80% of chronic hypoparathyroidism cases are caused by the accidental removal or damage to the parathyroid glands during surgery on the front part of the neck. The risk of permanent chronic hypoparathyroidism increases with total removal of the thyroid gland (thyroidectomy), repeated operations for bleeding, and central lymph node dissection (removal).

Yet, studies on risk factors for chronic hypoparathyroidism are scarce, as surgeons, endocrinologists, and family doctors tend to work separately within the perioperative period, which refers to the time from when the patient goes into the hospital or clinic for surgery until being discharged to go home.

Knowing this, investigators in Poland decided to look for factors related to developing permanent chronic hypoparathyroidism after total removal of the thyroid and lymph nodes in the central neck region of patients with thyroid cancer.

A total of 89 patients (ages 23 to 80) with papillary thyroid cancer were monitored on admission, and then daily, starting from postoperative day one until discharge from the hospital. Thereafter, tests were repeated every 7–14 days in 4–5-week intervals for one year, or until both active vitamin D (alphacalcidol) and calcium supplementation could be discontinued.

Blood levels of calcium, magnesium and PTH were decreased significantly across patients on day one after surgery. Importantly, on the same day, PTH levels decreased below the normal range (under 12 pg/ml) in 29 patients and were undetectable in 19 individuals (less than 6 pg/ml).

During the same time, all individuals with undetectable PTH had lower blood calcium concentration than what was measured in patients with higher PTH levels. However, calcium levels comparing permanent to transient hypoparathyroidism among those with untraceable PTH were not significant.

One year after the surgical intervention, 12 (13.6%) patients with undetectable PTH levels on day one required treatment for low blood calcium (hypocalcemia) and were diagnosed with permanent hypoparathyroidism. None of the other patients needed such treatment. Those with undetectable PTH, but not requiring treatment for hypocalcemia, were diagnosed with transient hypoparathyroidism.

Low PTH levels, caused by thyroid or parathyroid damage during surgery, lead to low calcium concentrations. Symptoms of too little PTH are essentially the same as those of hypocalcemia, so patients should be monitored closely. In line with prior studies, the researchers diagnosed hypoparathyroidism based on postoperative low calcium levels, instead of PTH deficiency. Ten of the 12 patients with hypocalcemia one year after after surgery had significantly lower PTH levels than before the surgery.

Also one year post-surgery, blood PTH concentration in patients with permanent hypoparathyroidism was significantly lower than in all patients who did not require treatment for prolonged hypocalcemia, and also was lower than in those with undetectable PTH on day one who had their calcium levels normalized.

“Undetectable POD1 [post-operative day one] PTH is an important risk factor of permanent HypoPT [hypoparathyroidism],” the researchers wrote.

The relative risk of permanent chronic hypoparathyroidism associated with undetectable levels of PTH was 88.75. Yet, the low number of patients in this study warrants caution regarding definitive conclusions, the scientists advised.

Although the development of hypoparathyroidism did not correlate with the number of parathyroid removed through surgery, the scientists also found that the main cause of permanent hypoparathyroidism was irreversible damage to the left parathyroid glands.