Med-Surg Endocrine System, part 14: Hypothyroidism & Myxedema Coma
by Cathy Parkes August 18, 2020 Updated: December 29, 2021 11 min read
In this article, we cover primary, secondary & tertiary hypothyroidism, and its related critical care topic: a myxedema coma. Knowing the pathophysiology, symptoms, diagnosis and treatment for these will be key in your Med-Surg exams as well as your nursing career.
These disorders are covered in our Medical-Surgical Flashcards (Endocrine system).
Hypothyroidism is a disease marked by inadequate production of T3 and T4, which are thyroid hormones from the thyroid gland.
TRH, TSH, T3/T4 hormone review
If you remember from our overview on thyroid hormones, the hypothalamus produces thyroid-releasing hormone (TRH), which causes the pituitary gland to produce thyroid-stimulating hormone (TSH), which prompts the thyroid gland to produce the thyroid hormones T3 and T4. You can think of the chain like this
- Hypothalamus produces TRH
- Pituitary gland produces TSH
- Thyroid produces T3/T4
Pathophysiology of hypothyroidism
To understand the differences between primary, secondary and tertiary hypothyroidism, you can flip the chain backwards (so that you are starting from the thyroid).
- Thyroid produces T3/T4
- Pituitary gland produces TSH
- Hypothalamus produces TRH
In primary hypothyroidism, there is a problem with the thyroid gland itself. If the thyroid gland is damaged, it cannot produce the T3 and T4 that it should. The leading cause of primary hypothyroidism is Hashimoto’s disease.
Hashimoto’s disease, also called chronic lymphocytic thyroiditis, is an autoimmune disorder that causes antibodies to attack and destroy the thyroid tissue. It occurs most commonly in middle-age women, but can occur in others.
Secondary causes of hypothyroidism occur when there is an issue with the pituitary gland, like a pituitary tumor. In this case, the pituitary gland is not functioning properly and therefore not producing enough TSH. Remember TSH is thyroid-stimulating hormone, so without the right stimulation, the thyroid gland is not prompted to make the correct amount of T3/T4.
Tertiary hypothyroidism occurs when there is a dysfunction of the hypothalamus. It creates a domino effect along the hormone pathway. If there is a problem with the hypothalamus, then it’s not producing enough TRH, so the pituitary gland is not being prompted to make enough TSH, so the thyroid gland doesn’t get the message to produce adequate T3/T4.
How to remember primary vs. secondary diseases
You can always remember that with a “primary” version of a disease, it means there’s an issue closest to the source, rather than several steps away along the chain. For example, in adrenocortical insufficiency, when the adrenal glands aren’t producing enough cortisol, the primary type is when there is a problem with the adrenal gland itself. In hyperparathyroidism, when the parathyroid gland is secreting too much PTH, the primary type is when there is a problem with the parathyroid glands themselves.
If you know which gland produces which hormone in which order, you’ll easily be able to understand whether a disorder is the primary, secondary or tertiary type. That’s why it’s so important to have a good understanding of the hormone pathways that lead to endocrine diseases and disorders. If you need a refresher, check out these A&P reviews we put together for the endocrine system in med-surg:
- Med-Surg Endocrine System, part 2: Organs, glands & hormone overview
- Med-Surg Endocrine System, part 3: Cortisol, T3/T4, GH, Estrogen, Progesterone, Testosterone, Oxytocin & Prolactin
- Med-Surg Endocrine System, part 4: ADH, Aldosterone & RAAS
- Med-Surg Endocrine System, part 5: Epinephrine, Norepinephrine, Calcitonin, PTH, Insulin & Glucagon
- Med-Surg Endocrine System, part 6: Negative Feedback Mechanism vs. Positive Feedback Mechanism
Signs and symptoms of hypothyroidism
The signs and symptoms of hypothyroidism include hypotension, bradycardia, lethargy, cold intolerance, constipation, weight gain, thin hair, brittle fingernails and depression.
If you want to think critically to deduce the signs and symptoms of hypothyroidism, remember from our hormone overview what T3/T4 controls:
- Metabolism. So when those hormones are low, the metabolism becomes sluggish and you see weight gain, cold intolerance (body temperature regulation), and lethargy.
- Heart function. So when those hormones are low, you see that slower heart function with bradycardia and hypotension.
- Digestion.So when those hormones are low, you see reduced digestive capabilities like constipation.
- Bone maintenance.So when those hormones are low, you see brittle fingernails.
When it comes to the lab values you might see with hypothyroidism, you will be looking at T3/T4 and TSH. The measurement of these hormones is known as a thyroid panel, which we explained in video 7 of this series. These are the most important endocrine lab values to know for your Med-Surg exams, whether a course final, your ATI or NCLEX. Lab values can be dispersed throughout your textbooks, which is why we created our Lab Values flashcards, to keep the most important lab values you need to know for your exams all in one place that’s easy to study!
- Primary hypothyroidism: Low T3/T4, high TSH
- Secondary hypothyroidism: Low T3/T4, low TSH
- Tertiary hypothyroidism: Low T3/T4, low TSH
T3/T4 values with hypothyroidism
In all types of hypothyroidism, you will see decreased T3/T4. That’s an easy one, because that’s what this disease is marked by!
The expected range for T3 in a thyroid panel is 70 - 204 ng/dL. T3 levels under 70 ng/dL can indicate hypothyroidism.
The expected range for T4 in a thyroid panel is 4 - 12 mcg/dL. T4 levels under 4 mcg/dL can indicate hypothyroidism.
TSH values with hypothyroidism
The TSH value you will get back in a thyroid panel for hypothyroidism really depends on if you are looking at primary, secondary, or tertiary hypothyroidism
With primary hypothyroidism, remember there is an issue in the thyroid gland itself causing inadequate production of T3/T4. However, the pituitary gland is functioning fine in this scenario, and its job is to make TSH to prompt the thyroid gland. It’s prompting desperately, but the thyroid is not responding. So with primary hypothyroidism, you will see elevated levels of TSH.
The expected range for TSH in a thyroid panel is 0.5 - 5.0 mU/L. TSH levels greater than 5 mU/L can indicate primary hypothyroidism when accompanied by low T3/T4.
With secondary or tertiary hypothyroidism, the pituitary gland is not functioning properly (by itself, or because of a dysfunctional hypothalamus) and therefore not producing enough TSH. So with secondary or tertiary hypothyroidism, you will see decreased levels of TSH.
TSH levels under 0.5 mU/L can indicate secondary or tertiary hypothyroidism when accompanied by low T3/T4.
Over the years, there have been periods of time when Cathy thought she had hypothyroidism. She noticed she was tired, cold, and had gained some weight. So she gets a thyroid panel, and every time, her T3, T4, and TSH levels were all normal. She always realizes sheepishly that she should cut back on her junk food and exercise more. Relatable!
The treatment for hypothyroidism is synthetic thyroid hormones, including levothyroxine (Synthroid, T4) and liothyroxine (Cytomel). These medications replace the thyroid hormones that the body is not producing enough of. The patient will need to take this medication as a lifelong treatment.
It’s important that this medication is taken on an empty stomach, so give this medication in the morning with a full glass of water, 30-60 minutes before a meal.
Levothyroxine is one of the essential medications you need to know for your Pharm exams and it’s covered in our Pharmacology flashcards.
Coordinating these early medications
In Cathy’s experience at the hospital, thyroid medications are usually scheduled for 6 AM. Cathy needs to wake these patients up at 6 AM with this medication and a full glass of water. Sometimes patients are not happy about this! So she came up with a strategy. If the patient with hypothyroidism needs labs drawn in the morning, Cathy coordinates it so they get labs drawn, their vitals taken, and their thyroid medication administered all at once. Then she can leave them alone!
Nursing care & patient teaching
For patients with hypothyroidism there are some nursing care and patient teaching tactics you can employ. Encourage frequent rest periods (to help with their lethargy). Encourage a low-calorie, high-fiber diet to promote weight loss and prevent constipation. Increase the patient's room temperature and provide blankets (to help with their cold intolerance).
This patient will need routine TSH/T3/T4 monitoring to ensure their medications remain therapeutic. The patient will also need to recognize signs of HYPERthyroidism (insomnia, tachycardia, heat intolerance, weight loss), as this can indicate their medication is working too well and needs to be adjusted.
Hypothyroidism is a disorder you need to know for your Med-Surg classes and exams, and a myxedema coma is a critical care topic that builds on your knowledge of this disorder.
Myxedema coma is a life-threatening complication of hypothyroidism known as decompensated hypothyroidism. Though this complication contains the word coma, patients may or may not be actually comatose. Either way, this is a medical emergency.
Myxedema coma can be caused by long-term untreated hypothyroidism, abrupt discontinuation of thyroid medication, or infection or illness. It can also be a combination of these. For example, in untreated hypothyroidism, the body comes up with adaptive mechanisms to maintain homeostasis, and if a bad infection occurs, these mechanisms can fail, and the body can fall into myxedema coma.
Signs and symptoms
The signs and symptoms of myxedema coma are very serious and include hypoxia (not enough oxygen), decreased cardiac output, decreased levels of consciousness (hence coma), bradycardia, hypotension and hypothermia.
Nursing care priorities
The most important nursing care priority when responding to a myxedema coma is maintaining a patent airway. That’s always the most important priority, which you know from the ABCs of nursing.
There’s a chance that this patient will need to be intubated and receive mechanical ventilation, so you will need to assist with that. Monitor the patient’s cardiac rhythm. Administer large doses of thyroid medications, like the aforementioned levothyroxine, as ordered. And you will need to warm this patient, since they have hypothermia with this condition.
Cathy’s teaching on hypothyroidism disorder and its complication myxedema coma is intended to help prepare you for Medical-Surgical nursing exams and critical care. The Medical-Surgical Nursing video series is intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI and NCLEX.
In this video, we are going to talk about hypothyroidism and myxedema coma. If you are following along with cards, I'm on card 34 [in the Endocrine system section of our Medical-Surgical Flashcard deck].
So with hypothyroidism, we have inadequate production of T3 and T4 which are thyroid hormones in the thyroid gland.
In terms of the pathophysiology behind hypothyroidism, causes could include primary, secondary, or tertiary causes.
So, just to do a little review here, the hypothalamus produces thyroid-releasing hormone TRH, which causes the pituitary gland to produce TSH or thyroid-stimulating hormone, and that allows the thyroid gland to produce T3 and T4.
So with primary hypothyroidism, that's where we have an issue with the thyroid gland itself. So the leading cause of primary hypothyroidism is Hashimoto's disease which is an autoimmune disorder that causes antibodies to attack and destroy the thyroid tissue. So if the thyroid gland is damaged, it can't produce its T3 and T4 like it should.
Secondary causes of hypothyroidism is where we have an issue with the pituitary gland, like if there was a pituitary tumor. This decreases production of TSH so the thyroid gland is not getting the message it needs to produce T3 or T4.
And then we have tertiary causes of hypothyroidism. So if there is some kind of dysfunction in the hypothalamus then the hypothalamus is not releasing TRH and therefore, the pituitary gland is not releasing TSH, and that is causing inadequate production of T3 and T4.
Hopefully that's helpful for you to be able to differentiate the three different causes of hypothyroidism.
Now, let's talk about the signs and symptoms of hypothyroidism. This includes hypotension, bradycardia, lethargy, cold intolerance, constipation, weight gain, thin hair, brittle fingernails, as well as depression.
In terms of what labs we may see, it really depends on whether we're dealing with primary hypothyroidism or secondary or tertiary hypothyroidism.
So with primary hypothyroidism, we have an issue in the thyroid gland itself. So it's been injured, and it's just not able to produce that T3 and T4. However, the pituitary gland is working just fine. So the pituitary gland is desperate to try to get this thyroid gland to produce its T3 and T4. So it's increasing levels of TSH. Be like, "Come on thyroid gland. Here's more TSH. Can you please get going on making your T3 and T4?" And the thyroid gland like, "Sorry, dude. I'm injured. I'm going to chill out. I can't produce any T3 or T4." So labs that you would see with primary hypothyroidism include low levels of T3 and T4 but elevated levels of TSH.
On the other hand, if you're dealing with secondary or tertiary hypothyroidism, this means that the thyroid gland itself is working fine but it's not getting the right signal from the pituitary gland. So the pituitary gland is not producing enough TSH and that makes the thyroid gland not produce T3 and T4. So if you look at the labs for secondary hypothyroidism, you're going to have low levels of T3 and T4 but you're also going to have low levels of TSH because there's some kind of pituitary tumor or the pituitary gland is not getting the proper signal from the hypothalamus. If there's a problem with the hypothalamus, that causes decreased TRH, which causes decreased TSH, which causes decreased T3 and T4. Okay? So those are the labs you can expect.
Over the years, I've had periods of time where I was feeling like, "Oh, I'm really tired and I'm cold all the time and I've kind of gained some weight. And maybe I have hypothyroidism." And I go and I get that checked out and all the time, my T3, T4, and TSH levels are all normal. So that has never been the problem. It's like, well, maybe I just need to stop eating so much and exercise more. That might work too. So I've never actually had any issues with my thyroid, but I've always suspected that I may have had those issues in the past.
Okay. In terms of treatment, we would give them a synthetic form of the thyroid hormones. So this would include levothyroxine or liothyroxine. So you would give this medication not with meals - so like an hour before meals - in the morning with a full glass of water.
At the hospital, they always schedule thyroid medications, levothyroxine or liothyroxine, at 6:00 AM. So you get to wake your patient up at 6:00 AM and give them their thyroid medication with a full glass of water. And, boy, are they happy to see you at 6:00 AM. Not. So a lot of times, if they have to have labs in the morning, I try to coordinate it all so they get their labs drawn, we could do their vital signs, and they get their thyroid medication all at once, so then I can leave them alone after that.
Okay. In terms of nursing care for a patient who has hypothyroidism, you want to encourage frequent rest periods because they have this lethargy, you want to encourage a low-calorie, high-fiber diet to help promote weight loss and to prevent constipation, and then you want to increase the patient's room temperature and provide blankets because they have this cold intolerance.
Okay, finally let's talk about myxedema coma, which is one of our critical care topics here in the Medical-Surgical Deck, Card 36 [Endocrine system].
This is where we have a patient with severe, life-threatening hypothyroidism, and it could be due to the fact that they have untreated hypothyroidism, or they may have abruptly discontinued their thyroid medication, or it could be due to infection or illness.
So signs and symptoms are very serious and include hypoxia as well as decreased cardiac output, decreased level of consciousness, bradycardia, hypotension and hypothermia.
So in terms of the nursing care priorities, we're going to want to maintain a patent airway, right? So our ABC priorities, airway is most important. There's a chance that this patient will need to be intubated and receive mechanical ventilation, so you're going to want to assist with that. You're definitely going to want to monitor the patient's cardiac rhythm and administer large doses of thyroid medications such as levothyroxine as ordered. And then warm the patient as they will have hypothermia with this condition.
Okay, that is it for hypothyroidism and in my next video, we will talk about hyperthyroidism. Thanks so much for watching, and if this information has been helpful, be sure to like this video and leave us a comment. Take care, and good luck studying!
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