15% of Patients Develop Permanent Hypoparathyroidism After Thyroid Surgery, Study Finds

Approximately 15% of patients undergoing surgery to remove the thyroid gland, called a thyroidectomy, develop permanent hypoparathyroidism, an analysis shows.

The extent and timing of the surgery, the expertise of the surgeon who performs the procedure, and the levels of calcium in the patient’s blood immediately after surgery are some of the factors that may predict whether or not a person permanently develops this condition, the analysis found.

The findings, “Prevalence and risk factors for hypoparathyroidism following total thyroidectomy in Spain: a multicentric and nation-wide retrospective analysis,” were published in Endocrine.

Hypoparathyroidism is a rare disorder caused by low levels of the parathyroid hormone (PTH) in the body. Normally, PTH is produced when the levels of calcium in the blood are low, to trigger its increase. Therefore, one of the consequences of low PTH levels is the marked decrease of calcium in the blood.

In many cases, hypoparathyroidism occurs in people who undergo neck surgery that causes permanent damage to the parathyroid glands, the structures responsible for producing PTH. This type is called post-surgical hypoparathyroidism.

“Most cases of hypoparathyroidism are transient [temporary] and resolved in the first 12 months after surgery, but the available estimates on the persistence of this hormone deficiency are highly variable [and inconsistent between studies], ranging from 0.12 to 12%,” the investigators said.

To learn more, a group of Spanish researchers set out to determine the prevalence of permanent hypoparathyroidism following thyroid surgery, and to explore factors that might predict patients’ clinical outcomes after the procedure.

The multicenter, retrospective, nationwide study involved a total 1,792 patients who underwent total thyroidectomy and were followed at different endocrinology clinics between January and March 2018. A total of 20 hospitals participated in the study.

The prevalence of hypoparathyroidism was assessed in all patients at four different time points: immediately after surgery; three to six months after surgery; one year after surgery; and at the last study visit.

Among the 1,792 study participants, 866 (48.3%) showed post-operative hypoparathyroidism immediately after surgery. Most of the patients eventually recovered from hypoparathyroidism, and the majority did so three to six months after surgery.

Further analyses revealed the prevalence of hypoparathyroidism decreased gradually over time, with 22.9% of patients still having hypoparathyroidism at the three-to-six month time point.

Only 14.5% had hypoparathyroidism at the last study visit, the researchers said.

The investigators found that several factors increased a patient’s chances of developing hypoparathyroidism after surgery. These included:

• The presence of parathyroid tissue on histology analyses performed on the tissue that had been removed during surgery
• Lymph node dissection (removal of lymph nodes)
• Having undergone a two-stage thyroidectomy (re-operating to remove the entire thyroid gland)

Conversely, they found other factors decreased the odds of hypoparathyroidism following thyroid surgery. Among them:

• Having high levels of calcium in the blood after surgery
• Being treated by a surgical team of experts
• Having thyroid cancer

“Although most patients with post-surgical hypoparathyroidism recover parathyroid function, the prevalence of permanent disease in clinical practice is non negligible (14.5%). Post-operative calcium, extent and timing of surgery, the presence of cancer, expert surgical team, and parathyroid tissue at histology are predictors of permanent hypoparathyroidism,” the researchers said.