Approach to hypothyroidism: Clinical sciences

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Introduction0:00–0:38

Hypothyroidism refers to low thyroid hormone levels, which leads to a reduction of the basal metabolic rate. Patients with hypothyroidism present with a wide spectrum of signs and symptoms which can range from subclinical disease to a lifethreatening condition called myxedema coma.
The diagnostic workup for hypothyroidism mainly involves checking thyroid stimulating hormone or TSH level and free thyroxine or free T four level to determine the cause of hypothyroidism.
Now, if your patient presents with chief concerns, suggesting hypothyroidism, you should first perform an ABCD E assessment to determine if your patient is unstable or stable if unstable, stabilize the airway breathing and circulation.

Unstable patient0:38–1:54

Next, obtain IV access and put your patient on continuous vital sign monitoring including heart rate, BP and pulse oximetry as well as cardiac telemetry.
Finally, if needed, provide supplemental oxygen. Now, here's a clinical pearl to keep in mind if your patient presents with hypothermia, bradycardia, hypoventilation and lethargy, you should suspect myxedema coma, which is a severe life threatening form of hypothyroidism.
Myxedema coma typically occurs later in patients with longstanding hypothyroidism treatment consists of supportive care which in some patients means ventilatory or circulatory support as well as corticosteroids and thyroid hormone and electrolyte replacement.
Any underlying precipitant such as an infection or heart failure should be identified and treated as well. All right, now that we're done with unstable patients, let's go back to the ABCDE assessment and discuss the stable ones.

Stable patient1:54–4:16

First. Obtain a focused history and physical examination.
Your patient will likely report symptoms suggesting a low basal metabolic rate and sympathetic activity including fatigue, weight gain and cold intolerance.
In addition, constipation is common and patients may develop depression, hair loss and even menstrual abnormalities. On the flip side, physical exam findings include cardiovascular manifestations such as bradycardia and diastolic hypertension as well as C NS findings primarily delayed relaxation of deep tendon reflexes.
Next, your patient can have dry skin, fragile hair and sometimes even nonpitting peripheral edema, often referred to as mixed edema.
My edema occurs due to the accumulation of mucopolysaccharides also called glycosaminoglycans in the dermis which bind to water molecules resulting in edema.
Finally, in some individuals, you might detect a palpable goiter at this point. You should consider hypothyroidism.
So your next step is to order A TSH and free T four, normal TSH and free T four reflects euthyroidism, which means the thyroid works properly.
So you should consider alternative diagnoses. Now, here's a clinical pearl to keep in mind, some patients with a severe acute illness, like acute myocardial infarction can have labs suggesting abnormal thyroid function in the absence of thyroid disease.
One common example is euthyroid sick syndrome also called nonthyroidal illness. In this case, TSH and free T four levels could be low or normal and T three levels are low due to reduced peripheral conversion of T four to T three.
Since E thyroid six syndrome isn't an actual thyroid disorder. There's no need for thyroid hormone replacement.
Instead, treatment should focus on addressing the underlying condition. That's why ideally hypothyroidism assessment should be performed in the absence of acute illness.
However, if TSH is high or even just mildly elevated and free T four is normal, you can diagnose subclinical hypothyroidism.

Subclinical hypothyroidism4:16–4:44

Keep in mind that these individuals are typically asymptomatic. So the diagnosis is based on abnormal lab findings.
All right. Now, let's go back and take a look at TSH and free T four levels.
If TSH is high and free T four is low, you can diagnose primary hypothyroidism. Next order anti thyroid peroxidase and anti thyroglobulin antibodies.

Hashimoto thyroiditis4:44–5:31

If either are present, you can diagnose hashimoto thyroiditis. Keep in mind that patients with hashimoto thyroiditis often experience an initial hyperthyroid phase, which is when the damaged thyroid tissue releases tons of preform thyroid hormones.
And then as the thyroid continues to atrophy over time, patients typically progress to develop chronic hypothyroidism. Now, let's take a look at when antibodies are not present.
Iatrogenic causes include previous neck radiation, radioactive iodine treatment or thyroid surgery as well as medications like amiodarone, lithium antithyroid medications or even iodine excess.

Iatrogenic hypothyroidism5:31–7:19

If your patient has a history of any of these diagnose iatrogenic hypothyroidism. In some cases such as following radioactive iodine treatment or partial thyroidectomy.
Hypothyroidism can be reversible and thyroid function may recover. On the other hand, hypothyroidism is typically permanent after total thyroidectomy or aggressive cancer treatments, particularly external beam radiation to the neck.
Here's a clinical pearl iodine deficiency is a well known cause of hypothyroidism. Since iodine is required for thyroid hormone production.
Nowadays, it's rarely seen in countries that have implemented public health measures such as iodine fortification of salt and bread.
Paradoxically due to an autoregulatory mechanism, such as the wolf Chiko effect, iodine excess can also trigger hypothyroidism, which is seen most commonly in individuals with autoimmune thyroiditis.
Similarly, amiodarone which has a high iodine content can cause thyrotoxicity manifesting as either hyperthyroidism or hypothyroidism.
In the case of lithium, it inhibits the uptake of iodine by the thyroid gland as well as the secretion of thyroid hormones.
This can cause hypothyroidism. Ok.
Now, if your patient has primary hypothyroidism, but you don't identify any iatrogenic cause, you can diagnose idiopathic hypothyroidism.

Idiopathic hypothyroidism7:19–7:35

Finally, let's go all the way back to our labs one last time. If TSH and free T four are both low, you can diagnose secondary hypothyroidism.

Secondary hypothyroidism7:35–8:34

A type of central hypothyroidism which occurs when the pituitary gland is affected and can't produce enough TSH to stimulate thyroid hormone production.
Secondary hypothyroidism usually occurs in the setting of pituitary, adenomas, intracranial tumors, infections or other destructive and inflammatory processes affecting the pituitary gland.
One important infiltrative condition that you should keep in mind is sarcoidosis. It's worth noting that besides TSH, other pituitary hormones may also be affected.
So you should also screen for associated pituitary hormone deficiencies like ach FSH, LH GH and prolactin. All right.
It's a quick recap. Hypothyroidism refers to any condition in which thyroid hormone levels are inappropriately low if a patient presents with signs and symptoms, suggesting hypothyroidism perform a focused history and physical exam and order A TSH and free T four.

Review8:34–9:40

If those are normal, consider alternative diagnoses. And if TSH is high and free T four is normal diagnose subclinical hypothyroidism.
On the other hand, if TSH is high and free T four is low, diagnose primary hypothyroidism and check antithyroid peroxidase and antithyroglobulin antibodies.
If those are present, diagnose hashimoto thyroiditis if they're not present, look for iatrogenic causes like neck radiation, radioactive iodine treatment, thyroid surgery or medications.
If the iatrogenic cause is identified diagnose iatrogenic hypothyroidism. But if no iatrogenic cause is found diagnose idiopathic hypothyroidism.
Finally, if both TSH and free T four are low, it's secondary hypothyroidism.