CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 45: H Y P O T H Y R O ID ISM
A 65-year-old female presents with weakness, fatigue, cold intoler-
ance, constipation, dry skin, and goiter.
Laboratory tests: TSH and free T4
Treatment: Thyroid hormone replacement with levothyroxine
C L IN IC A L C O R R E L A T IO N
Hypothyroidism is quite common in older adults and may present with an
indolent course, or it may induce dramatic mental changes such as coma or
pericardial effusion with tamponade. The most common etiology is primary
hypothyroidism, or failure of the thyroid gland to manufacture and release suf-
ficient thyroid hormone. The diagnosis is established by an elevated thyroid-
stimulating hormone (TSH). The treatment is by thyroxine replacement.
A PPR O A C H TO T H Y R O ID G L A N D
Be familiar with thyroid hormone metabolism.
Know about the regulation of thyroid hormones.
Understand the role of iodine on synthesis of thyroid hormone.
Graves disease: An autoimmune disorder in which antibodies overstimu-
late the production of thyroid hormones leading to a condition of hyper-
thyroidism, or elevated thyroid hormone synthesis and secretion.
Hashimoto thyroiditis: An autoimmune disorder in which the thyroid
gland is destroyed by the action of antibodies leading to a condition of
hypothyroidism, or decreased thyroid hormone synthesis and secretion.
Thyroid response elements: TRE; A domain on deoxyribonucleic acid
(DNA) that will bind the complex formed by thyroid hormone binding
to the thyroid hormone receptor. When the complex binds to the TRE,
which are located in the promoter region of the DNA, it activates tran-
scription of the gene. When thyroid hormone is not bound to the recep-
tor the receptor acts as a transcription repressor.
Thyroxine: T4; a thyroid hormone derived from the amino acid tyrosine
that contains four iodine atoms per molecule.