Let’s review the hypothyroid
disorders that we have talked about.
Primary hypothyroidism manifest with
an elevated TSH and low T4 and T3.
Key testing here would include
thyroid peroxidase antibodies
and if positive, the most likely
cause Hashimoto’s thyroiditis.
Remember the most common cause of
hypothyroidism in the United States.
Secondary or central hypothyroidism, you really manifest
biochemically with a low TSH and a low T4 or T3.
This is usually caused by a lack
of TSH from the pituitary gland.
You want to treat these patients to replace
the thyroid hormone with levothyroxine
but note that you cannot use the
TSH changes to guide your therapy.
Rather check serum T4 to gauge that you are
treating them adequately with thyroid hormone.
Subclinical hypothyroidism manifesting
with high TSH but normal T4 and T3
usually here we repeat the
TSH level in 2-3 months.
The euthyroid sick syndrome or nonthyroidal
Illness syndrome manifest with a low/normal TSH,
a low/normal T4 and a low T3.
The cause of this is reduced levels of thyroid hormone
binding proteins and halted activity of deiodinases
that widen counters in critically ill patients in the
hospitals, and no further assessment is necessary.