Is Levothyroxine Alone Adequate Thyroid Hormone Replacement?

Patients taking thyroid hormone replacement after thyroid removal surgery often report feeling differently than they did prior to taking thyroid hormone. The symptoms can include fatigue, worsening mood or subjective "brain fog" where the patient feels like their thinking is just not as sharp as it was previously. Multiple studies have found that patients taking thyroid hormone replacement have a diminished quality of life compared to matched controls. Previous studies have suggested that the type of deiodinase (DIO) polymorphism a patient has, which is responsible for converting the thyroid hormone T4 into the more biologically active T3, may contribute to their overall cognition and sense of well-being. The Investigators aim to determine if the type of deiodinase polymorphism a patient has contributes to the patient's cognition and overall sense of well-being after surgery and thyroid hormone replacement. Objective: Determine if patients with the deiodinase type 2 CC polymorphism have objective differences in working memory (N-back test is primary endpoint), cognitive function and sense of well-being after thyroidectomy when placed on standard thyroid hormone replacement therapy. Hypotheses: (1) Patients with the deiodinase type 2 CC polymorphism will have worse working memory (N-back test is primary endpoint), cognitive function and sense of well-being on standard thyroid hormone replacement therapy after thyroidectomy compared with before thyroidectomy. (2) Patients with the deiodinase type 2 TT or TC polymorphism will have no differences in working memory, cognitive function or sense of well-being on standard thyroid hormone replacement before and after thyroidectomy.