BACKGROUND
The parathyroid glands are usually 4 small glands that are next to the thyroid gland – 2 on each side. The parathyroid glands secrete parathyroid hormone (PTH) which regulates the body’s calcium levels. Damage to the parathyroid glands during surgery can lead to low calcium levels (hypocalcemia) which may be short-lived or, rarely, can be permanent. This risk is mainly during a total thyroidectomy when all 4 glands may be damaged. Lobectomies rarely cause hypocalcemia since at least 2 parathyroid glands are not at risk of being damaged.

The risk of injury to parathyroid glands and the resulting hypoparathyroidism causing hypocalcemia has long been a concern during a total thyroidectomy for thyroid cancer, and it carries major long term problems for patients. To reduce the risk of hypoparathyroidism during surgery, the parathyroid glands are individually identified and carefully preserved as possible. Sometimes, clearly damaged parathyroid glands are transplanted into surrounding muscle to preserve some function. However, it takes ~6-8 weeks for the transplanted parathyroid glands to regain function. Despite these efforts, up to 30% of patients undergoing total thyroidectomy have temporary hypoparathyroidism and 4% have permanent hypoparathyroidism. These percentages are lower with high volume thyroid surgeons.

New imaging technologies have been developed to increase the identification of the parathyroid glands and possibly decrease the rate of post-operative hypoparathyroidism. One of these new technologies is nearinfrared autofluorescence (NIRAF) imaging, which detects a specific optical signal of parathyroid tissue when an infrared light is directed at it. This signal allows the surgeon to distinguish parathyroid tissue from surrounding structures such as the thyroid gland.

Some previous studies have shown that this technology can help the surgeon to better identify parathyroid glands during surgery. The article discussed here is a randomized study comparing the postoperative hypoparathyroidism rates in patients undergoing total thyroidectomy with and without the aid of NIRAF technology.

THE FULL ARTICLE TITLE
Benmiloud F et al. 2020 Association of autofluorescencebased detection of the parathyroid glands during total thyroidectomy with postoperative hypocalcemia risk: Results of the PARAFLUO multicenter randomized clinical trial. JAMA Surg 155:106–112. PMID: 31693081.

SUMMARY OF THE STUDY
This study was a trial of patients 18 years of age or older undergoing a total thyroidectomy. The most important aspect of this study was the way in which the technology was used in the operating room. In the group without the technology, surgeons performed standard operation, and if parathyroid glands were identified, they would be preserved. In the technology group, a portion of the operative time was dedicated specifically to the use of the NIRAF device, taking care to find and preserve all four parathyroid glands. Patients were followed for 6 months to determine temporary (≤6 months) and permanent (>6 months) hypoparathyroidism.

The study included 241 patients who were randomly assigned – 120 to standard surgery and 121 to surgery aided by NIRAF. All 4 parathyroid glands were identified in the NIRAF group more often (47%) than in the standard surgery group (19.2%). The authors found that temporary postoperative hypocalcemia was significantly lower in the NIRAF group than in those treated with standard surgery. The risk of permanent hypoparathyroidism was not statistically different between groups.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that the use of NIRAF technology in patients undergoing total thyroidectomy improved identification of the parathyroid glands and decreased the risks of temporary postoperative hypoparathyroidism. There was no difference in the risk of permanent hypoparathyroidism. This is an important new technology that should be studied further.

— Alan P. Farwell, MD

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