Influence of prophylactic central lymph node dissection on postoperative thyroglobulin levels and radioiodine treatment in papillary thyroid cancer
Introduction: In treating papillary thyroid cancer (PTC), prophylactic central neck lymph node dissection with total thyroidectomy (TT) is controversial. This is because there is a possibility of increased morbidity with uncertain benefits. This study aims to determine whether prophylactic central neck dissection offers advantages over TT alone.
Methods: This was a retrospective cohort study. It examined patients with PTC without preoperative evidence of lymph node involvement. These patients were undergoing either TT or TT with bilateral central lymph node dissection (TT + BCLND).
Results: The study looked at patients who were treated from 2002 to 2009; there were 143 patients who had clinically node-negative PTC, and they underwent either TT (n=65) or TT + BCLND (n=78).
The two groups were similar in age, gender, tumor size, multifocality, angioinvasion, and metastasis/age/completeness-of-resection/invasion/size score.
In the TT + BCLND group, the presence of involved central neck lymph nodes upstaged 28.6% of patients to stage III disease. This resulted in higher radioactive iodine ablation doses following surgery.
The stimulated serum thyroglobulin levels before and 1 year after radioactive iodine ablation were equivalent in the 2 groups, as were the number of patients with undetectable stimulated thyroglobulin levels.
The incidence of post-operative infection (0.6%), hemorrhage (2%), recurrent laryngeal nerve injury (1.4%), and permanent hypoparathyroidism (1.4%) were similar between the groups. Temporary symptomatic hypocalcemia was more common in the TT+BCLND group (27%) than in the TT group (8%, p<0.01).
Recurrence rates were similar between the groups (2 recurrences in the central neck in each group). One patient in the TT group demonstrated distant metastases, and 2 patients in the TT+BCLND group had lateral neck recurrences.
Conclusion: Adding central lymph node dissection to TT for PTC patients upstages nearly one-third of the patients who are over the age of 45. This changes the radioactive iodine ablative therapy dose. However, it does not change the postoperative thyroglobulin levels or recurrence rates during a follow-up period of 2 years.
All thyroid surgeons agree that lymph nodes obviously involved with metastatic thyroid cancer in the central neck should be treated by clearance of these nodes via a central neck dissection at the time of thyroidectomy. The controversial issue remains what to do about lymph nodes that are clinically negative – they have no obvious appearance of harboring thyroid cancer metastases either before or during surgery. In this scenario, a central neck dissection would be termed prophylactic, rather than therapeutic. A recent multidisciplinary publication (Carty et al Thyroid. 2009 Nov;19(11):1153-8) presents a consensus view about the terminology, classification and anatomical details relevant for central neck dissection.
Numerous studies have argued both for and against prophylactic central neck dissection during surgery for papillary thyroid cancer. The publication by Hughes et al references these studies and presents findings from their patients. It does not claim to resolve the current controversy, especially given the limitations of non-randomized, retrospective design and relatively short follow-up period. The authors point out that, at least in the experienced hands of endocrine surgeons at their center, prophylactic central neck dissection is safe. The only higher complication rate was for temporary hypoparathyroidism. Thyroglobulin levels and recurrence in post-operative surveillance were similar between patients who did and did not receive this prophylactic procedure. Overall, one can infer that there is still no proven benefit for prophylactic central neck dissection.
However, the authors highlight an important consideration of their findings, namely that prophylactic central neck dissection does have consequences in staging of patients older than age 45. This, in turn, changes decisions for the dose of radioactive iodine ablation (RAI) in some patients and the avoidance of RAI in others. It is easy to appreciate the wisdom of therapy tailored to the needs of an individual patient. However, because there is not enough long-term data, it is difficult to draw strong conclusions about the ultimate impact of these choices. Undoubtedly, future studies will continue to explore the topic of prophylactic central neck dissection. They may identify patients who would most benefit from such surgery, while sparing low-risk patients from its potential risks.