Results

Characteristics of patients

Fifty patients who met the inclusion criteria were prospectively enrolled in this study and assigned to either the NIRAF group (n = 25) or the Non-NIRAF group (n = 25). There were no statistically significant differences between the two groups in terms of baseline data (P > 0.05) (Table 1).

 | NIRAF group (n = 25) | Non-NIRAF group (n = 25) | P value
Sex, n (%) |  |  | 0.19
Male | 8 (32.0) | 4 (16.0) | 
Female | 17 (68.0) | 21 (84.0) | 
Age (year), median (IQR) | 37.00 (29.00, 50.50) | 43.00 (35.50, 47.00) | 0.32
BMI (kg/m2), median (IQR) | 23.28 (21.03, 25.61) | 24.34 (21.70, 26.77) | 0.53
Preoperative PTH (pg/ml), mean ± SD | 35.40 ± 14.24 | 34.89 ± 10.00 | 0.88
Preoperative serum calcium (mmol/L), median (IQR) | 2.28 (2.22, 2.35) | 2.28 (2.25, 2.36) | 0.79

Postoperative outcomes

The comparison of biochemical markers after surgery was significant. Compared with the non-NIRAF group, PTH levels in the NIRAF group were significantly higher (P < 0.05) (Table 2). Precisely, the NIRAF group was 6 pg/mL higher on the first day after surgery and 2.47 pg/mL higher on the first month after surgery. Serum calcium levels showed no significant difference between the two groups on the first postoperative day (P > 0.05). However, the median (interquartile range) in the NIRAF group [2.18 (2.13, 2.35) mmol/L] was significantly higher than that in the Non-NIRAF group [2.13 (2.09, 2.18) mmol/L] on the first postoperative month (P < 0.05) (Table 2).

 | NIRAF Group (n = 25) | Non-NIRAF Group (n = 25) | P value
Resection Scope |  |  | 0.77
Unilateral resection, n (%) | 14 (56.0) | 15 (60.0) | 
Bilateral resection, n (%) | 11 (44.0) | 10 (40.0) | 
Surgical Safety |  |  | 0.33
Inadvertent parathyroidectomy, n (%) | 5 (20.0) | 8 (32.0) | 
Sensitivity | 80.0 | 68.0 | 
Specificity | 84.0 | NA | 
Postoperative Function |  |  | 
PTH (pg/mL) |  |  | 
Postoperative D1, median (IQR) | 26.20 (20.50, 33.16) | 20.20 (14.60, 24.25) | 0.002
Postoperative M1, median (IQR) | 30.90 (26.50, 44.55) | 28.43 (25.57, 30.42) | 0.04
Serum calcium ion (mmol/L) |  |  | 
Postoperative D1, mean ± SD | 2.12 ± 0.11 | 2.08 ± 0.15 | 0.29
Postoperative M1, median (IQR) | 2.18 (2.13, 2.35) | 2.13 (2.09, 2.18) | 0.03

Inadvertent parathyroidectomy events

In the NIRAF group, the sensitivity of parathyroid identification was 80%, and the specificity was 84%. Of all these patients, eight inadvertent parathyroidectomy events occurred in the Non-NIRAF group, whereas five occurred in the NIRAF group (Table 2). Although the difference between the two groups was not statistically significant (P > 0.05), the NIRAF group demonstrated a lower rate of parathyroid misidentification.

Impact of BMI on inadvertent parathyroidectomy

Regarding the relationship between baseline patient factors and the risk of inadvertent parathyroidectomy, univariate binary logistic regression demonstrated a significant association between higher BMI and the occurrence of inadvertent parathyroidectomy (P = 0.04, 95% CI: 1.01–1.76). However, after adjusting for potential confounders, including age and sex, in the multivariate binomial logistic regression analysis, this association did not strictly reach statistical significance (P = 0.07, 95% CI: 0.98–1.73).

False-positive events in NIRAF group

Table 3 summarizes the four false-positive events observed in the NIRAF group. Case 1 represents a typical false-positive instance, in which a thyroid nodule exhibited autofluorescence mimicking PGs (Fig. 1, A1–C1). In case 3, a suspected autofluorescent tissue was detected and confirmed by the pathology to be adipose tissue rather than PGs (Fig. 1, A3–C3). Similarly, other non-parathyroid tissues, such as the thymus (case 2) and lymph nodes (case 4), were also found to emit confounding autofluorescent signals (Fig. 1, A2–C2, A4–C4). Intraoperatively, these suspected fluorescent tissues were excised, separately labelled, and submitted for pathological examination, which ultimately confirmed that they were not parathyroid. Furthermore, no residual parathyroid tissue was found in the primary surgical specimens. No actual PGs were inadvertently removed. All four patients maintained normal parathyroid function. As shown in Table 3, their one-month postoperative PTH and serum calcium levels remained within normal ranges.

Case | Gender | Age | BMI (kg/m2) | Resection scope | PTH (pg/mL) | Serum calcium (mmol/L) | Pathological diagnosis | Biopsy detected tissue
Pre | Post D1 | Post M1 | Pre | Post D1 | Post M1
1 | Female | 33 | 22.58 | Bilateral | 21.70 | 27.60 | 32.50 | 2.34 | 2.11 | 2.14 | Nodular goiter | Thyroid Nodule
2 | Male | 41 | 28.40 | Unilateral | 54.40 | 42.80 | 60.90 | 2.31 | 2.27 | 2.30 | Thyroid carcinoma | Thymus
3 | Male | 30 | 33.22 | Bilateral | 44.40 | 24.00 | 40.68 | 2.39 | 2.16 | 2.37 | Thyroid carcinoma | Adipose Tissue
4 | Female | 52 | 23.47 | Unilateral | 37.20 | 15.80 | 26.19 | 2.23 | 2.22 | 2.43 | Thyroid carcinoma | Lymph Node

Fig. 1: Representative intraoperative endoscopic images of false-positive autofluorescence in the NIRAF group. Images are displayed in white-light (A1–A4), NIRAF (B1–B4), and fusion (C1–C4) modes. (A1–C1) Residual thyroid adenoma (green arrow) adjacent to the right superior PG (blue arrow). (A2–C2) Thymic tissue (green arrow). (A3–C3) Left adipose mass (green arrow) visualized alongside the left superior PG (blue arrow) and left inferior PG (orange arrow). (A4–C4) Lymph node in level VIB (green arrow) near the right inferior PG (blue arrow). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)