Time to Hypothyroidism Following Hemithyroidectomy.

Background The time to hypothyroidism post hemithyroidectomy is variable. There are multiple risk factors for developing hypothyroidism. The aim of this study was to identify the time of hypothyroidism and other predictors of hypothyroidism in euthyroid patients following hemithyroidectomy. Methods This was a retrospective study. Of 170 euthyroid patients who underwent hemithyroidectomy for benign disease between 2006 - 2014, age, gender, pre-operative thyroid function tests, body mass index (BMI), and other co-morbidities were examined to determine predictors of early (<3 months) or late (>3 months) hypothyroidism. A high normal preoperative thyroid stimulating hormone (HN-TSH) was defined as ≥2.01 uIU/ml, and a low normal TSH (LN-TSH) was defined as <2.01 uIU/ml. Results A total of 63 of the 170 patients (37%) became hypothyroid. At 3 months, 21.5% of patients were hypothyroid. At 6 months after operation, an additional 5% had become hypothyroid, and after 1 year, 8% more were hypothyroid. The only independent predictor of hypothyroidism was preoperative HN-TSH (≥2.01) (p<0.001) on multivariate analysis. Conclusion In addition to known predictors of hypothyroidism following hemithyroidectomy for benign disease, such as the size of the thyroid remnant, a history of neck irradiation, and coexisting thyroid autoimmune disease, a BMI ≥35 kg/m, age ≥45, and preoperative HN-TSH are risk factors for postoperative hypothyroidism within 3 months of operation. Such patients should be closely monitored.