The present study showed that post-lobectomy complications developed rarely after thyroid lobectomy, even when combined with CND. The overall complication rates appeared to be quite low as compared to those after total thyroidectomy . However, post-lobectomy hypothyroidism was a major clinical problem, because a considerable number of patients required thyroid hormone replacement therapy. A previous systematic review reported the pooled risk of post-lobectomy hypothyroidism as 22% (range, 7−49%) . Two studies also showed the incidence of subclinical hypothyroidism (defined as TSH level > 4.5 mIU/L) after hemithyroidectomy occurred in as many as 55.8% (226 of 405 patients) and 64.2% (215 of 335 patients) of post-lobectomy cases [14, 26]. In most cases (84.5%), the condition developed in the early postoperative months (1–3 months postoperatively) . Another study showed that hypothyroidism might develop in 43.3% (145 of 335 patients) within 12 months post-lobectomy and in 20.9% (70 of 335 patients) thereafter and that 119 of 215 (55.3%) patients with such hypothyroidism eventually recovered to euthyroid state . A further study also showed that increased TSH levels > 2 mIU/L occurred in 59% patients within 12 months after thyroid lobectomy . The present study also showed the elevation of serum TSH levels at 1–6 months after lobectomy and the need for T4 supplementation in most patients undergoing thyroid lobectomy.
The 2015 ATA guidelines recommend maintaining the TSH level of 0.5–2 mIU/L after thyroid lobectomy for low-risk thyroid cancer . In the present study, the proportions of patients with the need for T4 supplementation were found 82.3% at 3 ~ 6 months and 66.7% at 1 year after lobectomy. A recent study also showed that a high proportion of 168 study patients met the criteria for T4 supplementation (TSH levels > 2 mIU/L) after lobectomy: 67.9% at 6 weeks with a median TSH of 3.73 and 76.2% at 6–12 months with a median TSH of 3.43 . Preoperative TSH level was a sole significant predictor associated with meeting criteria for TSH suppression (OR = 1.70, 95% CI = 1.06–3.40, P = 0.04) . The same result was found in the present and previous multiple studies: high preoperative TSH levels were a significant risk factor for post-lobectomy hypothyroidism [14, 25–29]. A meta-analysis has shown that other factors associated with increased risk for hypothyroidism are anti-thyroid peroxidase antibody-positivity (48% vs. 19%, P = 0.001) and a high degree of thyroid inflammation (49% vs. 10%, P = 0.006) . There is still controversy whether TSH suppression therapy increases RFS and overall survival rates in patients undergoing thyroid lobectomy [19, 20]. Further details on this issue might be skipped. In addition, the T4 supplementation lowering serum TSH level might be balanced with its potential risk of several metabolic complications, e.g., cardiovascular disease and osteoporosis [30, 31]. Further prospective studies are required to elucidate the role of TSH suppression therapy in post-lobectomy patients .
The present study showed a very low rate of recurrence after thyroid lobectomy for PTC. During a median follow-up period of 72 months, post-lobectomy recurrence occurred in only 4 (1.1%) patients, with high RFS rates. Adam and colleagues  found the overall survival of lobectomy cases similar to those with total thyroidectomy in the patients with PTC > 1 cm, although more LN, extrathyroidal and multifocal diseases were found in patients with total thyroidectomy. Thyroid lobectomy appeared to result in a survival outcome equal to that achieved by total thyroidectomy in stage I PTC patients < 45 years of age . A previous study also showed the overall low recurrence rate and high cause-specific survival rate after thyroid lobectomy in 1088 PTC patients with a median follow-up of 17.6 years . At 25 years after lobectomy, remnant thyroid, regional LN, and distant site recurrence rates were 93.5%, 90.6%, and 93.6%, respectively. They advocated that lobectomy in PTC patients aged < 45 years and with a tumor size of ≤ 4 cm was a valid alternative to total thyroidectomy. Another study also showed excellent outcomes in terms of recurrence: only 23 (3.1%) of 734 PTC patients with thyroid lobectomy developed recurrent diseases . They found a 10-year recurrence rate of 0.8% versus 7.8% in the cases without and with extrathyroidal extension, respectively. The safety for extended applications of lobectomy, e.g., in PTC with extrathyroidal extension, multifocality, and other adverse findings, as well as tumor size 1.1–4 cm, should be further examined. In our cohort, considerable numbers of patients had adverse pathological findings. The intermediate- or high-risk patients might have an increased probability for post-thyroidectomy recurrence, which appears to be diminished by implementing unilateral CND combined with thyroid lobectomy . However, this should be examined by further studies for the initial optimal extent of surgery in LN dissection as well as thyroidectomy.
Our study had the potential limitations of a retrospective design. A few cases of PTC > 1 cm were included in our study because the criteria of tumor size for lobectomy strictly followed the previous version of the ATA guidelines . Routine performance of CND in our study patients is not supported by the previous and current ATA guidelines [6, 15]. However, this approach did allow us to gain accurate pathological nodal information, and other clinical and pathological findings defined considerable numbers of patients with intermediate or high risk in our studies. This information might facilitate further revisions of the current guideline for the extended applications of thyroid lobectomy for differentiated thyroid cancer. Long-term follow-up to obtain accurate information on post-lobectomy recurrence might also be required.
In conclusion, our data show that thyroid lobectomy for PTC localized to a single lobe is associated with a low recurrence rate, but is significantly associated with post-lobectomy hypothyroidism. After thyroid lobectomy, a considerable number of patients had the elevation of serum TSH concentrations > 2 mIU/L and the need for TSH suppression to the level of 0.5-2.0 mIU/L. Preoperative TSH level can predict the need for post-lobectomy TSH suppression therapy. This might help identify patients who are likely to require thyroid hormone supplementation.