Prevalence of endogenous normal thyroid function three years after hemithyroidectomy for differentiated thyroid cancer

Objective
To investigate the prevalence of endogenous normal thyroid function 3 years after hemithyroidectomy for low-risk differentiated thyroid cancer if a postoperative thyroid-stimulating hormone increase up to 4 mIU/L is accepted.

Method
A retrospective review of a total of 162 Eastern Danish patients was conducted. Patients were initially followed up without levothyroxine treatment after hemithyroidectomy for differentiated thyroid cancer if thyroid-stimulating hormone was below 4 mIU/L, in accordance with the Danish treatment guideline. Patients’ hospital charts were reviewed, and data on the initiation of levothyroxine treatment, pre- and postoperative thyroid-stimulating hormone, recurrence, and remnant lobe nodularity were collected.

Results
A total of 143/162 (88%) did not take levothyroxine before hemithyroidectomy, with a median (interquartile range) age of 53 (43–65) years; 80% were women. During follow-up, the prevalence of endogenous normal thyroid function gradually decreased to 80, 69, and 66% after 1, 2, and 3 years. Concomitantly, hypothyroidism developed with thyroid-stimulating hormone >4.0 mIU/L in 20, 31, and 34% of patients, who were replaced with levothyroxine. In patients not on levothyroxine, TSH was significantly increased within the normal range 1, 2, and 3 years after hemithyroidectomy for DTC (P < 0.0001). 4/143 (3%) had completion thyroidectomies due to growth of preexisting nodules; no patient had a recurrence.

Conclusion
One-third of differentiated thyroid cancer patients require levothyroxine treatment 3 years after hemithyroidectomy if postoperative thyroid-stimulating hormone levels up to 4 mIU/L are accepted. Avoidance of levothyroxine treatment happens at the expense of a significant increase in thyroid-stimulating hormone levels.