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

Objective: To investigate the prevalence of endogenous normal thyroid function three 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 one, two, and three 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 one, two, and three 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 three years after hemithyroidectomy if postoperative thyroid stimulating hormone levels up to 4 mIU/L is accepted. Avoidance of levothyroxine treatment happens at the expense of a significant increase in thyroid stimulating hormone levels.