Neurocognitive and Metabolic Effects of Mild Hypothyroidism
Neurocognitive and Metabolic Effects of Mild Hypothyroidism
Patients with hypothyroidism are routinely treated with thyroid hormone (l-thyroxine) for
 replacement therapy. Physicians monitor the thyroid hormone dose by measuring a thyroid
 stimulating hormone (TSH) level in the blood, with the goal of a normal level. However,
 recent data suggest that the "normal" TSH range is too broad, and that patients may still
 have symptoms if their TSH levels are at the top or bottom part of the normal range.

 To study this issue, it is useful to address issues such as general health status,
 psychological symptoms, mood, memory, and metabolic status, since thyroid hormone has major
 effects on the brain and metabolism, and since patients with treated hypothyroidism often
 have symptoms related to these areas.

 In the present study, otherwise healthy subjects with treated hypothyroidism, ages 20-75
 years, will be enrolled in a 7-11month study. At baseline, they will have tests of health
 status, psychological symptoms, mood, memory, body composition, and energy expenditure
 performed. Following these baseline measurements, subjects will receive either their usual
 doses of l-thyroxine, or a slightly higher or lower dose. The doses will be chosen to try to
 achieve either a low-normal TSH level, a high-normal TSH level, or a mildly elevated TSH
 level. Which target TSH the patient is assigned will be determined randomly, and neither the
 subject nor the study contacts will know which dose the patient is receiving. Subjects will
 be seen every 6 weeks during the study for brief visits to make sure they are not having any
 side effects, and to adjust the l-thyroxine doses if the TSH has not yet reached the target
 range. At the 24-week visit (end of study), the subjects will undergo the same tests that
 they had on the baseline visit.

 Results from the study will be examined to see if minor changes in TSH or other thyroid
 hormone levels cause changes in any of the outcomes, and if the degree of TSH change
 correlates with the degree of outcome changes. These results may help physicians caring for
 patients with thyroid disease better determine the optimal dose of thyroid hormone for each
 patient.
Thyroid hormone is essential for neurocognitive and metabolic function, and patients with
 overt thyroid dysfunction have well-described alterations in mood, cognition, energy
 expenditure, and body composition. However, it is not clear that patients with more mild
 degrees of thyroid dysfunction have clinically significant alterations in these parameters.

 In addition, recent data suggest that variations in thyroid function within the laboratory
 reference range may also affect these parameters.

 Patients with hypothyroidism are routinely treated with levothyroxine (L-T4) as replacement
 therapy. Physicians monitor the L-T4 dose by measuring serum thyroid stimulating hormone
 (TSH) levels, with the goal of a normal level. However, many patients with normal TSH levels
 continue to report symptoms, primarily in neurocognitive and metabolic areas. For this
 reason, patients with hypothyroidism often request higher L-T4 doses, but the clinical
 consequences of this are unknown.

 In the present study, otherwise healthy subjects with treated hypothyroidism and normal TSH
 levels, ages 20-75 years, will be enrolled in a 7-11 month study. At baseline, the following
 tests will be performed to measure health status, psychological symptoms, mood, memory, body
 composition, and energy expenditure: the Short Form Health Survey-36 (SF-36), Profile of Mood
 States (POMS), Affective Lability Scale (ALS), Letter Cancellation Test (LCT), Trail Making
 Test, Iowa Gambling Task (IGT), N-Back Test, Subject-Ordered Pointing, Paragraph Recall,
 Pursuit Rotor, Motor Sequence Learning Test, resting energy expenditure (REE) and thermic
 effect of food (TEF) by indirect calorimetry, total energy expenditure (TEE) by doubly
 labelled water, physical activity energy expenditure (PAEE) by accelerometry, diet intake by
 24-hour diet recalls, and body composition by dual energy x-ray absorptiometry (DEXA).
 Following these baseline measurements, subjects will receive either their usual doses of
 L-T4, or a slightly higher or lower dose. The doses will be chosen to try to achieve either a
 low-normal TSH level, a high-normal TSH level, or a mildly elevated TSH level. Which target
 TSH the patient is assigned will be determined randomly, and neither the subject nor the
 study contacts will know which dose the patient is receiving. Subjects will be seen every 6
 weeks during the study for brief visits to make sure they are not having any side effects,
 and to adjust L-T4 doses if the TSH has not yet reached the target range. At the 24-week
 visit (end of study), the subjects will undergo the same tests that they had on the baseline
 visit.

 Results from the study will be examined to see if minor changes in TSH or other thyroid
 hormone levels cause changes in any of the outcomes, and if the degree of TSH change
 correlates with the degree of outcome changes. These results may help physicians caring for
 patients with thyroid disease better determine the optimal dose of thyroid hormone for each
 patient.
Inclusion Criteria:

 -  Ages 20-75

 -  Primary hypothyroidism on stable dose of L-T4 for > 3 months

 -  Documented elevated TSH off L-T4

 -  Normal TSH level on usual dose of L-T4

 -  No acute or chronic medical or psychiatric illnesses that affect thyroid function,
 mood or cognition

 -  No medication use that affects thyroid function, mood or cognition (oral
 contraceptives or estrogen therapy allowed)

 -  Normal score on screening Mini-Mental State Exam (MMSE) (to test for dementia)

 -  Normal vision by screening examination

 -  Normal hearing by screening examination

 -  Non smoker

 Exclusion Criteria:

 -  Failure to meet any of the above inclusion criteria

 -  Inability to speak and comprehend English

 -  A history of coronary artery disease

 -  Screening hgb <10

 -  Screening wbc > 10,000

 -  Clinically significant abnormalities on screening metabolic set

 -  Screening LDL cholesterol > 160

 -  Screening triglyceride > 300

 -  Significant abnormalities on screening ECG

 -  Pregnancy or intent to become pregnant in next 6 months

 -  Present or recent use of medications that affect thyroid hormone levels or interfere
 with thyroid hormone effects, including beta-blockers, lithium, glucocorticoids, or
 iodine containing agents

 -  MMSE score < 26