Risk factors for the development of hypothyroidism after hemithyroidectomy.

OBJECTIVES To assess the incidence of hypothyroidism after hemithyroidectomy and to identify risk factors for the development of hypothyroidism. DESIGN Retrospective analysis. SETTING A tertiary care academic medical center. PATIENTS The study included 90 patients who underwent a hemithyroidectomy from 1999 to 2004. MAIN OUTCOME MEASURES Hypothyroidism was defined as a serum thyrotropin level greater than 6.0 mIU/L at least 8 weeks after hemithyroidectomy. All patients were analyzed for age, sex, surgical indications, preoperative and postoperative thyrotropin levels, weight of resected specimen, final pathologic analysis, and length of follow-up. Multivariate analysis was performed to identify multiple risk factors for the development of hypothyroidism. RESULTS The final pathologic analysis demonstrated 49 follicular adenomas, 17 cases of Hashimoto thyroiditis, 10 multinodular goiters, and 14 other abnormalities. The overall incidence of the development of hypothyroidism after hemithyroidectomy was 27% (24 of 90 patients). When the groups were broken down by pathologic diagnosis, the incidence of hypothyroidism developing during follow-up among the Hashimoto thyroiditis and multinodular goiter groups was 59% and 50%, respectively. Also, the patients who developed hypothyroidism were noted to have statistically significant higher preoperative serum thyrotropin levels (3.15 mIU/L vs 1.95 mIU/L; P<.001) than those who remained euthyroid. There was no relationship between age, sex, or weight of the resected tissue and the subsequent risk of hypothyroidism. CONCLUSIONS The overall incidence of posthemithyroidectomy hypothyroidism was 27%, and the majority of cases developed in the first 6 to 12 months after surgery. Risk factors for the development of hypothyroidism include pathologic diagnosis (Hashimoto thyroiditis and multinodular goiter) as well as a high-normal serum thyrotropin level. Routine monitoring of serum thyrotropin levels should be performed in all patients who undergo a hemithyroidectomy.