Comparative Study of Clinical Outcomes for Total Thyroidectomy/Lobectomy and Isthmusectomy in Patients with Isthmic Papillary Thyroid Carcinoma

<b><i>Background:</i></b> The optimal surgical extent for isthmus-confined papillary thyroid carcinoma (PTC) remains unclear. We aimed to evaluate the clinicopathological characteristics, surgical complications, and recurrence rates based on the extent of resection. <b><i>Methods:</i></b> This retrospective cohort study included 345 patients who underwent thyroidectomy for solitary isthmus-confined PTC at two affiliated tertiary centers from 2013 to 2022. Patients were excluded if they had multifocal PTC with lobar involvement, large tumors (>4 cm), suspected extrathyroidal extension (ETE), clinically positive lymph nodes (LNs), or aggressive histological subtypes. Clinicopathological features, surgical complication rates, and recurrence rates were compared among the total thyroidectomy (TT), lobectomy (L), and isthmusectomy (I) groups. This retrospective cohort study used propensity score matching (PSM), resulting in two groups of 85 patients: TT/L and I. <b><i>Results:</i></b> Among the 345 included patients, 89 underwent TT, 30 underwent L, and 226 underwent I. After PSM, 170 patients were analyzed. The mean age was 48.2 years, and the mean tumor size was 0.8 cm. Microcarcinoma accounted for 71.8% of cases. The rates of ETE (65.3%), multifocality (9.4%), <i>BRAF</i> mutation (75.3%), and Hashimoto's thyroiditis (19.4%) were observed without significant differences between the TT/L and I groups. Risk stratification for central LN metastasis showed no significant difference (high-risk: 21.2% vs. 27.1%, <i>p</i> = 0.353). No recurrence or distant metastasis was observed in either group during a median follow-up of 4.3 years. Median follow-up was longer in the TT/L group (6.1 years [interquartile range (IQR): 4.0-8.5] vs. 3.6 years [IQR: 2.1-4.9], <i>p</i> < 0.001). Major complications were more frequent in TT/L group: transient/permanent hypocalcemia (14.1%/1.2% vs. 0%/0%) and transient vocal cord palsy (3.5% vs. 0%). Levothyroxine dependency was significantly higher in the TT/L group in terms of usage (90.6% vs. 34.1%, <i>p</i> < 0.001), average administered dose (85.5 ± 45.1 µg vs. 21.9 ± 33.2 µg, <i>p</i> < 0.001), and duration (5.2 ± 3.1 years vs. 0.9 ± 1.3 years, <i>p</i> < 0.001). Newly noted thyroid lesions occurred more frequently in the I group (1.3% vs. 10.6%, <i>p</i> = 0.039). <b><i>Conclusions:</i></b> Isthmusectomy may be considered for carefully selected patients with isthmus-confined PTC. Validation in long-term prospective studies is warranted.