Incidence and Risk Factors for Development of Hypothyroidism after Hemithyroidectomy

Abstract

Objectives: To evaluate the incidence of hypothyroidism after hemithyroidectomy and possible risk factors to predict postoperative hypothyroidism. Methods: We performed a prospective study of patients with non - toxic thyroid disease undergoing hemithyroidectomy between May 2015 and June 2018 at the Department of Otorhinolaryngology, Samutsakhon hospital. Only preoperative euthyroid patients were included. The preoperative thyroid antibodies and histopathology of thyroid specimens were collected. The thyroid function test was evaluated at two months and six months after surgery. Results: One hundred and six patients were recruited for the present study, twenty patients (18.9%) developed hypothyroidism (6 patients overt or symptomatic hypothyroidism, 14 patients subclinical hypothyroidism) at two months after surgery and nineteen patients (17.9%) developed hypothyroidism (7 patients overt or symptomatic hypothyroidism, 14 patients subclinical hypothyroidism) at six months after surgery. The mean preoperative thyrotropin level was significantly higher in the hypothyroid group than in the euthyroid group (2.3 ± 1.3 vs 0.7 ± 0.5 micro IU / ml), The preoperative high normal thyroid stimulating hormone (TSH) > 2 micro IU / ml) developed hypothyroidism 89.5% in contrast to only 8.1% of those the preoperative TSH ≤ 2 micro IU / ml (odds ratio 97.1). In anti-thyroid microsomal antibody test, the rate of post - operative hypothyroidism among patients with elevated thyroid antibody had statistically significant difference from those with normal thyroid antibody result (p = 0.03). The preoperative high normal TSH (> 2 micro IU /ml), anti-thyroid microsomal antibody and anti-thyroglobulin antibody positive titer showed 100% positive predictive value and 80.4% negative predictive value. Conclusion: The incidence of hypothyroidism after hemithyroidectomy was 18.9% at two months after surgery and 17.9% at six months after surgery. The preoperative high normal TSH > 2 micro IU /ml, elevated thyroid antibodies indicated thyroiditis were good pre-operative predictive markers. Such high risk patients needed close follow up TSH monitoring before the onset of clinical hypothyroidism.