Preserving at least three parathyroid glands is key to avoiding permanent hypoparathyroidism — resulting in abnormally low calcium levels in the blood and bones, and an increase in phosphorus in the blood — after thyroid removal surgery, research shows.
Hypoparathyroidism is a common complication of total thyroidectomy, or the complete removal of the thyroid, and can cause many painful symptoms. While the efficacy of parathyroid cell autotransplants has been questioned, preserving the parathyroid glands — small glands located in the neck — has remained an important strategy for maintaining normal calcium levels after surgery.
Researchers at Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubiran, in Mexico, assessed the rate of postoperative hypocalcemia — low blood levels of calcium — and permanent hypoparathyroidism at their heathcare center. They also evaluated the risk factors and impact of parathyroid autotransplants, in which parathyroid tissue is placed into the muscle of either the neck or forearm.
The analysis included a total 956 patients, including 844 women (mean age 46.8 years, range 11
–88 years), who had undergone total thyroidectomy between 2000 and 2016. Medical records were used to study patient features, clinical presentation, management, and postoperative complications. All patients had at least one year of clinical follow-up, with a mean duration of 72.7 months.
Serum levels of calcium and phosphate were obtained 24 hours after surgery. However, levels of parathyroid hormone (PTH) were determined only in suspected cases of hypoparathyroidism. Hypocalcemia was defined as serum calcium levels less than 8 mg/dL.
Among the patients evaluated, a total 642 (67.2%) had thyroid cancer, 214 (22.4%) had multinodular goiter, and 41 had (4.3%) follicular adenoma. Multinodular goiter is an enlarged thyroid with multiple nodules, while follicular adenoma is a benign encapsulated tumor of the thyroid gland. Central neck lymph node dissection was performed in 459 (48%) cases.
Postoperative hypocalcemia occurred in 314 (32.8%) patients, 138 (43.9%) of whom recovered during the first month after surgery. The rate of transient hypoparathyroidism was 14.4%, the researchers said. In turn, the rate of protracted hypoparathyroidism was 18.4%, and the rate of permanent hypoparathyroidism was 3.9%.
The researchers noted that protracted hypoparathyroidism was defined as receiving calcium supplementation and having a PTH level below 13 after one month, but less than 12 months after surgery. Meanwhile, permanent hypoparathyroidism was described as needing calcium supplementation, with or without active vitamin D and magnesium, to achieve normal calcium levels for at least 12 months.
Patients with permanent hypoparathyroidism had significantly higher body mass index, and rate of central compartment neck dissection — the surgical excision of lymph nodes, commonly done with thyroid removal in the treatment of thyroid cancer. Those with normal calcium levels had the lowest proportion of metastasis — when cancer cells spread throughout the body — at diagnosis.
Oral calcium supplements were given to 396 (41.4%) patients, while 158 (16.5%) required intravenous calcium infusion followed by oral supplementation. Intravenous delivery of calcium during the first 48 hours post-surgery was administered to 127 (40.4%) individuals with postoperative hypocalcemia, as well as 99 (56.3%) with protracted hypoparathyroidism, and 31 (83.8%) with permanent hypoparathyroidism.
Researchers noted several key risk factors that were significantly associated with experiencing permanent hypoparathyroidism, including obesity and maintaining two or fewer parathyroid glands. Other risk factors were concomitant level VI lymph node dissection, and incidental removal of parathyroid glands without autotransplantation.
“Appropriate intraoperative parathyroid identification with in situ preservation [in the original place] of at least three glands might be the most important strategy to prevent transient and permanent postoperative hypoparathyroidism,” the scientists said.
“A meticulous surgical dissection of parathyroid glands” also is key in avoiding incidental parathyroidectomy, they added.