New Imaging Device Reduces Hypocalcemia After Thyroidectomy

Nancy A. Melville

November 12, 2019

Autofluorescence imaging using near-infrared light (NIRAF) to identify parathyroid glands during thyroid surgery is associated with a significant 65% reduction in the rate of post-operative hypocalcemia, as it allows for visualization of the glands well before they can be seen with the human eye, new research shows.

"Autofluorescence imaging provides images of the parathyroid glands at a very early stage, which may help improve parathyroid preservation during thyroid surgery," first author Fares Benmiloud, MD, a general surgeon with the European Hospital, Marseille, France, told Medscape Medical News.

Benmiloud, who is a consultant for Fluoptics, the manufacturer of the imaging device used in the study, presented the findings from the randomized trial here at the American Thyroid Association (ATA) 89th Annual Meeting.

The device used in the study, as well as another similar one, were approved for use a year ago by the US Food and Drug Administration for real-time location of parathyroid tissue during surgical procedures.

Asked to comment, Leonidas H. Duntas, MD, PhD, said the results suggest potentially important benefits from the use of autofluorescence in total thyroidectomy.

"This is a promising technique because it us to prevent inadvertent parathyroidectomy and to further prevent hypocalcemia, which is a burden for the patient," Duntas, a professor, Endocrinology, Diabetes and Metabolism Unit, at University of Athens Medical School, Greece, told Medscape Medical News.

Parathyroid Gland Identification in Thyroidectomy Tricky, But Important

The identification of the parathyroid glands during a total thyroidectomy can be challenging, and if the glands are inadvertently damaged, patients can develop postoperative hypocalcemia, a potentially serious complication.

Previous research has shown that, when subjected to near-infrared light, parathyroid glands emit a natural autofluorescent signal from which images can be produced, allowing for identification of the parathyroid glands before they can be manually visualized.

To evaluate the potential benefits of the imaging approach on the prevention of hypocalcemia, Benmiloud and colleagues randomized 241 patients at three hospitals in France from September 2016 to October 2018 who were undergoing total thyroidectomy to have additional NIRAF assistance (Fluoptics) during the procedure (n = 121) or a conventional thyroidectomy (n = 120).

Patients were a mean age of 53.6 years and 79.3% were women. Those with less-than-total thyroidectomies and pre-existing parathyroid diseases were excluded.

Over 60% of Glands Identified With NIRAF Before Seen With Naked Eye

For the primary outcome of the rate of hypocalcemia, 9% of those treated with NIRAF assistance developed temporary postoperative hypocalcemia (defined as a calcium level of < 8 mg/dL at postoperative day 1 or 2), compared with 22% in the conventional thyroidectomy group (P = .006).

There were no significant differences between the NIRAF and control groups in terms of permanent hypocalcemia (0% vs 1.6%).

After a multivariate analysis accounting for a number of factors, including surgical center and surgeon heterogeneity, use of NIRAF had an adjusted odds ratio for hypocalcemia of 0.35 (95% CI, –0.15 to 0.83; P = 0.02) compared with conventional surgery.

In terms of secondary outcomes, significantly fewer patients in the NIRAF group experienced parathyroid autotransplantation (4 [3.3%] vs 16 [13.3%]; P = .009).

And, importantly, fewer patients in the NIRAF group had inadvertently resected parathyroid glands (3 [2.5%] vs 14 [11.7%]; P = .006).

The authors note that 61.6% of parathyroid glands were identified with NIRAF before they were visible with the naked eye.

Important Findings but Imaging Has a Learning Curve

With temporary hypocalcemia representing a highly undesirable outcome, the findings are important, Benmiloud told Medscape Medical News.

"Temporary hypocalcemia can be severely symptomatic — even life-threatening if not treated,” he said. “It needs to be monitored and, in general, treated by oral calcium calcitriol for an unpredictable duration of time."

"This can result in treatment-related complications, such as skin necrosis in case of calcium gluconate extravasation, symptoms like constipation during oral treatment, or hypo/hypercalcemia after discharge, (and) additional healthcare costs associated with extended hospitalization, or rehospitalization, fees," he noted.

One caveat of this approach, however, is that clinicians need to learn and become familiar with reading autofluorescence images, Benmiloud said.

But the benefits appear to make that process worthwhile.

"There is a learning curve to interpret correctly the images found, to make the difference between fluorescent images corresponding to parathyroids and false positive images," he explained.

At the beginning of this learning curve, using the auofluorescence imaging takes a few minutes longer, "but with experience, this time is counterbalanced by the time saved in the procedure," Benmiloud observed.

Of note, the median duration of operation in the study was 99 minutes with NIRAF and 91 minutes with the conventional approach (P = .002).

"This is a new technique, and the future will tell if the results we had are generalizable, and if a reduction of permanent postoperative hypocalcemia can be achieved," Benmiloud concluded.

Duntas agreed that more research is needed.

"We need additional studies, but we hope (the approach) will be further improved and the studies will show it can be validated," he said.

"It appears safe and I think it can be helpful also in predicting autotransplantation," he concluded.

American Thyroid Association (ATA) 89th Annual Meeting. Abstract #26. Presented November 1, 2019.

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