Is Levothyroxine Alone Adequate Thyroid Hormone Replacement?

STUDY DESIGN Many patients undergo thyroidectomy for nodular thyroid disease. They have
normal thyroid function prior to surgery and are immediately placed on standard thyroid
hormone replacement therapy (levothyroxine, LT4) after surgery. The levothyroxine dose is
titrated every 6-8 weeks to normalize the thyroid stimulating hormone (TSH) level. The
investigators aim to study this population before surgery when the patients still have
endogenous thyroid function and after surgery once their TSH has been normalized to
pre-surgery levels. Using a weight based dosing strategy (1.6mcg/kg), most patients will
remain euthyroid throughout this process. This experimental design eliminates many of the
confounding variables that have plagued previous thyroid replacement trials. One of the most
difficult aspects of conducting these types of studies is testing a uniform patient
population. The most common cause of hypothyroidism is autoimmune thyroiditis (Hashimoto's
thyroiditis) and previous studies have largely focused on these patients. The difficulty in
testing patients with autoimmune thyroid failure is that even though they have a common
illness, the disease course is extremely variable. Each patient may have different degrees of
thyroid failure and may still be making different amounts of endogenous thyroid hormone. The
presence of thyroid autoantibodies has also been reported to have systemic effects, and may
influence perception of overall health and sense of well-being. This study will focus on a
more homogenous population without the potential cofounders inherent to patients with
autoimmune thyroid disease. Each patient will serve as their own control and also avoid any
cognitive or somatic effects that temporary hypothyroidism may induce.

No study has ever evaluated a patient's symptoms before and after replacement with thyroid
hormone when the patient is euthyroid before thyroid hormone therapy. The assumption has been
made that if serum TSH is normalized, thyroid hormone levels are adequate and that symptoms
of hypothyroidism have been relieved. The investigators know from large community based
studies that symptoms of hypothyroidism persist despite what the investigators believe is
"adequate" thyroid hormone replacement in as many as 10% of patients. Our study will be the
first to test the same patient, before and after thyroidectomy so the investigators can
directly compare normal endogenous thyroid function with levothyroxine (LT4) therapy
resulting in the same serum TSH. Thyroidectomies are often performed for large nodules or
nodules that show indeterminate or suspicious cytology after fine needle aspiration biopsy,
but turn out to be benign at final histological diagnosis. The current standard of care is to
replace thyroid hormone with LT4 to normalize the serum TSH. Our approach uses the same
patient as their own control and eliminates numerous variables that cannot be controlled for
in other studies including: variable onset of hypothyroidism, degree of endogenous thyroid
function and underlying cause of hypothyroidism.

Prior to and after surgery, the investigators will measure each patient's thyroid levels
(TSH, free T4, total T4, total T3, thyroxine binding globulin, sex hormone binding globulin,
lipid panel, and iron), and parathyroid/calcium function (parathyroid hormone, calcium,
albumin, vitamin D25), and deiodinase type 2 polymorphism status will be determined on
pre-surgery bloodwork. Thyronamine levels will also be measured before and after surgery.
Thyronamines are thyronergic metabolites of thyroid hormones that can decrease metabolism and
induce behavioral inactivity in mouse models. A recently developed sensitive chemiluminescent
antibody assay for 3-Iodothyronamine has been developed and patients on levothyroxine therapy
after thyroidectomy had higher thyronamine levels compared with euthyroid controls. Based on
these studies, the investigators hypothesize, as a secondary measure that patients with a
higher thyronamine level after surgery, or greater pre- vs post-surgery thyronamine level
will have worse outcomes, defined by the questionnaires. Patients will complete a series of
questionnaires (SF-36 measure of overall health, Billewicz measure of thyroid health, HADS
measure of anxiety and depression) as well as undergo working memory testing using the N-back
and cognitive function testing using the Sustained Attention to Response Test (SART). Lab
analysis will also be performed before surgery to look at targets of thyroid hormone action
including low density lipoprotein (LDL) cholesterol and sex hormone binding globulin (SHBG).
Following surgery, only patients benign results or low-risk differentiated thyroid cancer not
requiring radioiodine therapy or TSH suppression will continue on the study. The patients
continuing in the study will have their dose of levothyroxine titrated with the goal of
matching their pre-surgery TSH +/- 1 milli-international units per liter (mIU/L). 6 months
following surgery, lab testing, questionnaires and cognitive testing will be repeated. Timing
the second set of testing 6 months will allow adequate time to match the post-surgery TSH to
the pre-surgery level and give adequate time for any cognitive effects resulting from the
surgery itself to dissipate. The primary endpoint will compare changes in scores on the
N-back test before and after surgery from those in the deiodinase CC polymorphism group to
those in the deiodinase type 2 TC and TT groups. Secondary endpoints will include scores on
the SART and well-being questionnaires before and after surgery to correlate with deiodinase
polymorphisms as well as correlation of these outcome measures with serum thyronamine levels
before and after surgery as an exploratory measure.

An optional sub-study is being made available to research subjects to compare the stool
microbiota longitudinally, with the initial stool sample at the start of the study in the
presence of normal systemic thyroid hormone levels and then again after thyroidectomy while
taking oral levothyroxine. Comparisons of any microbiota compositional changes from before
and after surgery will be made to any changes in symptoms, cognition/memory testing and
overall quality of life. Any exposure to antibiotics, probiotics or other updates to medical
history will be documented at each visit. Any exposure to systemic antibiotics in the
previous 60 days of the first study collection or between collections will be excluded.
Subjects will complete a 3-day lead-in dietary log prior to each stool collection,
summarizing meal compositions on 3 consecutive days before the stool sample is collected and
submitted. Participants will be given their own dietary log again and encouraged to follow a
similar diet prior to the second stool collection.

Inclusion Criteria:

- TSH in the ideal reference range (0.4-4.0 milli-international units per liter (mIU/L))

- Planned thyroidectomy for nodular thyroid disease or low-risk differentiated thyroid
cancer (<4cm, no ETE, no expected use of RAI or suppressive levothyroxine therapy)

Exclusion Criteria:

- History of psychiatric illness (major illness as defined by DSM IV: major depression,
schizophrenia, mania, etc). Patients prescribed chronic medications for psychiatric
illness, those taking benzodiazepines or anti-seizure medication.

- Estrogen therapy that is new within the last 6 weeks or if the dose has been changed
within the last 6 weeks

- Positive thyroid antibodies

- Chronic use (>4 weeks) of concomitant medications that could affect cognition and
memory (including sedative hypnotics, selective serotonin reuptake inhibitors,
selective serotonin-norepinephrine reuptake inhibitors, Topamax, benzodiazepines,
etc.)

- Pregnancy

- Steroid therapy

- Persistent cancer of any type or other major medical illness