Study Points to Risk Factors for Post-surgery Hypoparathyroidism

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by Forest Ray PhD |

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Being female, thyroid size, and having to undergo a second surgery are associated with the occurrence of short-term hypoparathyroidism following removal of the thyroid, according to a recent study.

Risk factors for long-term hypoparathyroidism, the study also found, include thyroid size and low levels of the parathyroid hormone (PTH) on the first day after surgery.

The study, “Analysis of Risk Factors for Hypoparathyroidism After Total Thyroidectomy,” was published in the journal Frontiers in Surgery.

Hypoparathyroidism, characterized by abnormally low levels of the PTH hormone, often occurs after thyroid removal, or thyroidectomy. This surgery most is often done because a tumor has developed on the thyroid, which can be either benign (non-cancerous) or malignant (cancerous).

Although more often seen as a short-term, or transient condition, a few patients experience long-term hypoparathyroidism.

The risk factors involved in either short- or long-term hypoparathyroidism remain incompletely understood, however, prompting a group of researchers at the Shanghai Jiaotong University, in China, to analyze patient records from their hospital, for possible risk factors.

The group found 537 records from from January 2015 to December 2018. The patients within this group had an average age of 47.3 years and nearly three quarters of them were female.

Most cases (495, or 92.2%) involved a malignant tumor, the vast majority (489) being cases of papillary carcinoma — the most common type of thyroid cancer.

Following surgery, 194 patients experienced transient hypoparathyroidism, while 21 developed long-term cases.

Notably, transient cases were defined as blood calcium lower than 2.2 millimol (mmol)/L or parathyroid hormone lower than 7 picograms (pg)/ml. Oral calcium supplements and vitamin D3 were given to patients with hypoparathyroidism (low PTH levels at six months post-surgery).

Among those with transient cases, 135 had abnormally low PTH levels and 156 had abnormally low blood calcium levels, a characteristic complication of hypoparathyroidism that is associated with numbness in the fingers and toes, among other symptoms. Of the long-term cases, 19 had abnormally low PTH and two had normal levels but needed calcium supplementation to maintain normal blood calcium levels.

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The investigators determined that the main risk factors linked to transient hypoparathyroidism within this set of patients were:

  • being female;
  • lymph node dissection (surgery to remove cancerous and potentially cancerous areas of lymph nodes, often required during a thyroidectomy);
  • the maximum diameter of a patient’s thyroid;
  • having a second operation;
  • preoperative blood calcium.

“Regarding the size of the thyroid and the second operation, it is believed that the increase in the size of the thyroid and the difficulty of neck anatomy will cause the reduction of the surgical field and the difficulty of identifying and protecting the parathyroid glands,” the scientists wrote.

As for long-term hypoparathyroidism, the associated risk factors were lymph node dissection, maximum thyroid diameter, and below-normal PTH levels on the first day after surgery (d1PTH).

“For patients whose d1PTH is less than normal,” the researchers wrote, “calcium and vitamin D3 supplementation should be strengthened.”

Patients who do not get enough calcium supplementation or who fail to receive close follow-up visits, “may miss the chance of parathyroid function recovery.”