Study of Resistance to Thyroid Hormone After Long-term Exposure in People With Thyroid Cancer

Inclusion Criteria:

* Age 18 or older
* Due to a diagnosis of thyroid cancer, patient underwent a total thyroidectomy based on pathology.
* No evidence of active disease based on routine surveillance testing showing no suspicious findings on neck ultrasound and low thyroglobulin levels (≤1.0 ng/ml) with negative thyroglobulin antibodies within one year of study enrollment. For the study patients, this response can be evaluated after five years of TSH suppression. For control subjects, this response can be evaluated after two years of surveillance.
* Two groups:

  * 8 patients with a history of thyroid hormone suppression (TSH\<0.5 mU/L) for at least 5 years
  * 8 patients with no history of TSH suppression
* Normal TSH level based on the laboratory reference range for at least 6 months at the time of study enrollment.
* Blood pressure range of \>90/60 and \<180/100. Patients may be included in the study if blood pressure has been treated with medication and normalized.

Exclusion Criteria:

* Patient reported history of symptomatic heart disease including unstable angina or NYHA stage III or IV heart failure.
* Patient reported history of one of the following cardiac arrhythmias: atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia, ventricular fibrillation, or ventricular tachycardia.
* Patient reported history of uncontrolled hypotension (\<90/60) or hypertension (\>180/100).
* History of renal dysfunction with creatinine more than 1.5 times the upper limit of normal based on recent laboratory testing
* Known hypersensitivity to the drug
* Pregnant or breast feeding
* Prior history of seizures or brain damage
* Patients on chronic therapy with levodopa
* Patients on therapeutic doses of acetylsalicylic acid (2 - 3.6 gm/day)
* Patients with conditions that result in disruption of the hypothalamic-pituitary axis (i.e. hypophysectomy, hypopituitarism, pituitary tumor/surgery, head irradiation, or head trauma).