Hashimoto's thyroiditis is the most frequent cause
of pimary hypothyroidism in the United States.
It's also known as chronic
a positive TPO antibody test will be present and initially
they may actually have symptoms of hyperthryoidism,
subsequently progressing to
The management of this condition, in patients
with TSH greater than 10 microunits per mL,
daily levothyroxine replacement is taken on an
empty stomach to aid absorption in the jejunum.
The dose is titrated base on
thyroid stimulating hormone levels
measured 6-8 weeks after
any dose adjustments
Thyroid hormone deficiency usually implies
low circulating thyroid hormone levels.
It's more prevalent in women
than men with 2% versus 0.2%
and those with other automimmune disorders.
The top ten causes of thyroid
hormone deficiency is as follows:
Hashimoto's thyroiditis is by
far the most common in the US,
followed by iodine deficiency which
is the most common cause worldwide
Thyroid surgery with subsequent thyroid
hormone deficiency is another cause,
radioactive iodine therapy, external beam
radiation to the neck for malignancies
Medications like lithium and
amiodarone, as well as interferon,
and tyrosine kinase inhibitors can
inhibit thyroid hormone production.
Pituitary tunors, severe head trauma
and pituitary surgery are rarer causes
And then finally, cranial irradiation
which may cause central hyperthyroidism.
The signs and symptoms of
hypothyroidism are numerous.
Starting with the symptoms, patients
usually complain of being fatigued,
being intolerant to the
cold, having constipation.
In women they may complain of heavy
menses, they may complain of weight gain,
they may also have impaired concentration.
They note very dry skin and puffiness
which is related to the presence of edema
Also they can have mood changes,
They may complain of muscle cramps,
myalgias and reduced fertility.
On physical exam, patients with
hypothyroidism have fairly classic features.
There may be reduction in
basal body temperature.
They may also note diastolic hypertension
or high diastolic blood pressure.
They may be bradycardic
when the heart rate is low.
On examination of the skin and the hair, the hair
be dry and brittle - the hair may also fall out easily.
they may complain of baldness,
and patients can also be hoarse
One of the classic features on neurologic exam is
delayed relaxation phase of the deep tendon reflexes.
and this is pretty classic
On standardized testing like USMLE-CK, this would
usually be given in the stem of the question
where they want you to think of
hypothyroidism as a possible cause.
And then finally, enlargement of the thyroid gland or
goiter is a common accompaniment to hypothyroidism.
Subclinical hypothyroidism is
another interesting entity.
This usually manifest with an elevated TSH level
with a normal T4 level in asymptomatic patients.
The TSH levels normalizes in up to 30%
of the patient by 6 weeks on its own.
Elevated total cholesterol, LDL cholesterol
and C-reactive protein levels may also occur.
The treatment for this condition is only recommended
when the TSH level is greater than 10 microunits per mL
as this may be a risk factor for coronary
artery disease and congestive heart failure.
A goal TSH level of less than or
equal to 2.5 microunits per mL
is recommended for women with subclinical
hypothyroidism and a positive TPO antibody
who are planning to get pregnant.