Quantitative Autofluorescence Index Enhances Intraoperative Differentiation of Normal and Pathologic Parathyroid Glands

Highlight

This study introduces the autofluorescence index, a quantitative measure of parathyroid gland heterogeneity using near-infrared autofluorescence, which can reliably distinguish pathologic from normal glands intraoperatively. An autofluorescence index threshold ≥2.5 strongly indicates a gland is hyperfunctional, assisting surgeons in challenging cases, especially differentiating single adenomas and multigland hyperplasia.

Background

Primary hyperparathyroidism is a common endocrine disorder characterized by overactivity of one or more parathyroid glands leading to hypercalcemia and associated complications such as osteoporosis, kidney stones, and neurocognitive dysfunction. Surgical removal of hyperfunctional parathyroid tissue remains the definitive treatment. However, accurately identifying pathologic glands versus normal counterparts during parathyroidectomy can be challenging, particularly in cases of multigland disease or normohormonal presentations.

Near-infrared autofluorescence imaging has emerged as a promising technique for intraoperative parathyroid gland visualization by exploiting endogenous tissue fluorescence. While prior studies demonstrated the potential to distinguish parathyroid glands from surrounding tissues, clear metrics to differentiate hyperfunctional (adenomatous or hyperplastic) glands from normal parathyroids in real-time have not been established.

Study Design

This prospective observational study enrolled 72 patients undergoing curative parathyroidectomy for classic or normohormonal primary hyperparathyroidism. A near-infrared autofluorescence device was used intraoperatively to interrogate all identified parathyroid glands.

Two parameters of autofluorescence heterogeneity were calculated for each gland: variability (difference between maximum and minimum fluorescence values) and the autofluorescence index (maximum fluorescence/minimum fluorescence ratio). The primary outcome was the ability of the autofluorescence index to discriminate pathologic glands from normal glands during surgery. Receiver operating characteristic (ROC) curve analysis was applied to determine optimal threshold values for differentiation.

Key Findings

The surgical cohort included 57 patients with single adenomas, 5 with double adenomas, and 10 with four-gland hyperplasia. All patients achieved cure following surgical intervention.

Pathologic parathyroid glands showed significantly greater heterogeneity in autofluorescence signals, reflected by higher variability and autofluorescence index values, compared to normal glands.

For single adenomas, an autofluorescence index ≥2.4 reliably predicted pathologic glands with an area under the ROC curve (AUC) of 0.90, indicating excellent discrimination. Similarly, glands in four-gland hyperplasia exhibited an autofluorescence index threshold of ≥2.5 with an AUC of 0.86 to distinguish hyperplastic glands from normal tissue.

No significant correlation was observed between autofluorescence index and gland weight, reinforcing that fluorescence heterogeneity is independent of gland size and provides distinct diagnostic value.

Expert Commentary

The introduction of a quantitative autofluorescence index is a significant advancement for intraoperative parathyroid gland identification. By providing an objective, real-time metric, it addresses a critical unmet need—especially when visual appearance or biochemical markers are ambiguous. Previous research has noted variable autofluorescence among glands but lacked a robust, standardized intraoperative cutoff to directly inform surgical decision-making.

From a mechanistic perspective, altered cellular composition and metabolic states in hyperfunctional glands may contribute to differential autofluorescence patterns, though further studies are needed to elucidate these biological underpinnings.

Study limitations include the relatively small number of multigland hyperplasia cases and the single-center design, which may affect generalizability. Future multicenter trials could validate these findings and integrate autofluorescence index measurements with other emerging modalities (e.g., radioguided surgery, intraoperative PTH assays) to optimize parathyroidectomy outcomes.

Conclusion

The autofluorescence index is a novel, quantitative intraoperative tool that enhances the surgeon’s ability to differentiate hyperfunctional from normal parathyroid glands during parathyroidectomy. An index ≥2.5 reliably indicates adenomatous or hyperplastic glands and can guide resection strategies, potentially reducing operative times and improving cure rates. Broader adoption and further validation of this technique may transform parathyroid surgery, particularly for complex cases with ambiguous gland status.