Hypothyroidism After Hemithyroidectomy

The risk of hypothyroidism after hemithyroidectomy is variable, and most estimates come from single institutional studies. The purpose of the present study was to determine the incidence of hypothyroidism at the population level, and to evaluate predictive factors for hypothyroidism after hemithyroidectomy. This retrospective study identified euthyroid patients who underwent hemithyroidectomy between 2000 and 2010 for benign disease in Kaiser Permanente Southern California regional hospitals. The incidence of hypothyroidism [thyroid stimulating hormone (TSH) levels > 4 mu IU/ml] was analyzed. The independent effect of age-quartile, gender, race, thyroiditis, and preoperative TSH level on the development of hypothyroidism was evaluated. Of 1,240 euthyroid patients identified, 417 (34 %) developed hypothyroidism, and 314 (25 % of total group) needed levothyroxine. Hypothyroidism was more common in age-quartile 2 (32 %), age-quartile 3 (37 %), and age-quartile 4 (42 %) than in age-quartile 1 (25 %) [adjusted odds ratio (OR) = 1.87; 95 % confidence interval (CI) 1.27-2.76, p = 0.002; age-quartile 4 compared to age-quartile 1]. Hypothyroidism was more frequent with increasing preoperative TSH levels 36, 72, and 92 % in patients with TSH levels of 1.0-2, 2.01-3, and 3.01-4 mu IU/ml, respectively, compared to 17 % in those with TSH levels < 1 mu IU/ml [adjusted OR = 45.1; 95 % CI 13.5-151, p < 0.0001; 3.01-4 mu IU/ml compared to < 1 mu IU/ml]. Thyroiditis was also an independent predictor of hypothyroidism. About one third of euthyroid patients who undergo hemithyroidectomy develop hypothyroidism. The most significant predictor is the preoperative TSH level, with an approximate doubling of risk for each 1 unit of TSH increase over 1 mu IU/ml. Our categorical scale is simple and allows for easy recall when counseling patients preoperatively.