36 Year Old Woman With Thyroid Disorder

A 36 year old woman presents with a three month history of unintended weight loss, sensation of increased anxiety, heat intolerance, and reports, "I feel like my heart is going to beat right out of my chest." In addition, she reports a two-month history of increased frequency and looseness of stools. Physical exam reveals 3-4 plus Achilles and patella reflex response, mild exophthalmosis, bilateral fine tremor, and a diffusely enlarged non-tender thyroid. Heart rate 115 beats per minute at rest without murmur or other cardiac abnormalities. 

Considering thyroid disorder as her working diagnosis, which of the following would be her anticipated lab results?

A. Elevated TSH with normal limit free T4

B. Low TSH with elevated free T4

C. Elevated TSH with a low free T4

D. Normal limit TSH

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Transcript

Voiceover: Welcome to NP Certification Q&A presented by Fitzgerald Health Education Associates. This podcast is for NP students studying to pass their NP certification exam. Getting to the correct test answers means breaking down the exam questions themselves. Leading NP expert Dr. Margaret Fitzgerald shares her knowledge and experience to help you dissect the anatomy of a test question so you can better understand how to arrive at the correct test answer. So, if you're ready, let's jump right in.

Margaret Fitzgerald: A 36-year-old woman presents with a three-month history of unintended weight loss, sensation of increased anxiety, heat intolerance, and reports, quote, "I feel like my heart is going to beat right out of my chest." In addition, she reports a two-month history of increased frequency and looseness of stools. Physical exam reveals 3-4 plus Achilles and patella reflex response, mild exophthalmosis, bilateral fine tremor, and a diffusely enlarged non-tender thyroid. Heart rate 115 beats per minute at rest without murmur or other cardiac abnormalities. Considering thyroid disorder as her working diagnosis, which of the following would be her anticipated lab results? 

A. Elevated TSH with normal limit free T4

B. Low TSH with elevated free T4 

C. Elevated TSH with a low free T4

D. Normal limit TSH and a low free T4

The correct answer is B. Low TSH with an elevated free T4. 

Where should you start with this question? First, ask what kind of a question this is. Given that we're provided with a general diagnosis, just “thyroid disorder”, and we're asked to analyze and synthesize lab data. This is actually an assessment question. might look like a diagnosis question, but it's more an assessment question because you're taking some information that you've been given. Now, you need to analyze and synthesize those data and work towards the diagnosis. 

A bit of background information. This is an interesting question format and that it's given us that general term thyroid disorder but doesn't advise us whether they're looking for subclinical hypothyroidism, hypothyroidism or hyperthyroidism. 

So let's take a moment and think of what the thyroid does. The thyroid releases two main hormones T3 and T4. The majority of T3 in the body is a product of T4 conversion. So only a little bit of T3 comes directly from the thyroid. These thyroid hormones affect the action of every single cell in the body and their main function is facilitating cellular energy release. As a result, thyroid disease presents no matter what form as multiorgan disease. When there's too much thyroid hormone, too much available free T4, then there's excessive cellular energy release throughout the body. One way of thinking about this is if the body was a car engine, if the thyroid's not releasing enough T4, then you would not be able to get that engine to do anything other than a slow idle. take that car out of park, but no matter what you do, the car is just going to creep along really slowly. That of course describes hypothyroidism, where the DTRs are hypoactive, the heart rate at rest can be slower, skin is coarse and dry from poor cell turnover, and there's a general lack of energy. Now what's being described in this patient there's excessive cellular energy release hyperthyroidism and it is because the thyroid itself is releasing too much T4 the body's engine is in hyperdrive pedal to the floor you're going to have tachycardia at rest unintended weight loss and report of frequent low volume loose stools and hyperreflexia. 

The most common form of hyperthyroidism seen in North America is Graves’ disease which is autoimmune in nature. And what we have here with this patient is classic presentation of Graves’ disease, exophthalmos, an enlarged thyroid and obviously clinical evidence of hyperthyroidism. This condition usually presents fairly acutely with a relatively short period of symptoms, usually less than a few months. And that's exactly what we see here. In addition, and I've mentioned this on countless other podcasts, we always want to be looking on boards for the condition to present in the group who is most likely to have this disease. And who does hyperthyroidism most often present in? Women between the ages of 30 to 50 years and the clinical presentation is as Graves’ disease as I just mentioned. Interestingly enough, with hypothyroidism, often times you see that patient who's presenting with hypothyroidism and they've been dragging their tails around for a year, two years, whatever it is. But hyperthyroidism, most people come in relatively quickly for that. 

With this information in mind, let's break down the question one more time. 36-year-old woman presents with a three-month history of unintended weight loss, sensation of increased anxiety, heat intolerance, and reports, quote, "I feel like my heart is going to beat right out of my chest." I'm going to do a little something different this time and chop this question into sections, go over them because you could see once we read the entire question, you can tell their anticipated response is something about thyroid disease. Since you know that once you've read the entire question and this reinforces the importance of reading the entire question before attempting to answer this, you should be starting to develop a thought as to whether the thyroid is hyper or hypoactive. And what we have here is weight loss. Remember, always, always, always classify weight loss as intended or unintended cause weight loss is almost always a cause of concern. We also have with this patient increased sensation of anxiety, heat intolerance, and elevated heart rate. Automatically, you should turn your thoughts through the presentation of hyperthyroidism. In other words, the body's engine is all revved up, pedal right down to the floor. Additionally, in the question, we're told, additional history includes a two-month history of increased frequency and looseness of stools. Physical exam reveals three to four plus Achilles and patellar DTR response, mild exophthalmosis, bilateral fine tremor and diffusely enlarged thyroid with heart rate at 115 beats per minute without murmur or other cardiac abnormalities. Quick stop here. Going back to the car analogy, this car engine is on high rev. The loose stools, the three to four plus Achilles patella reflex all add up to this. Please keep in mind normally DTR response is 2 plus not 3 to 4 plus. So this is an example of hyperreflexia. Then throw in the tremor and the elevated heart rate at rest. we have more of that hyperthyroid picture. Now going to turn to the physical exam. Enlarged non-tender thyroid that's consistent with goer and the exophthalmos the bulging of both eyes. These are all components of Graves’ disease. The most common form of hyperthyroidism in North America. 

Now the rest of the question is going to ask you, you believe this is hyperthyroidism as your most likely diagnosis. What are you going to see in the labs? So what does the question say? Consider thyroid disorder as her working diagnosis. Which of the following would be her anticipated lab results? A. An elevated TSH and a normal limit free T4. Obviously, this is incorrect and this would describe subclinical hypothyroidism, which is a typically asymptomatic condition. The patient we're looking at has symptoms. A low TSH with an elevated free T4. This is the correct answer. Recall where is TSH released from? The anterior lobe of the pituitary. and it informs the thyroid how much T4 and T3 to release. What's happening here is the thyroid because it's diseased is releasing hormone all on its own in excessive amounts. In response, the anterior lobe of the pituitary pulls back on TSH release. And so what the anterior lobe of the pituitary is saying is no need to stimulate the thyroid because there's ample thyroid hormone free T4 cruising around because the thyroid is releasing it on their own. This is the classic laboratory presentation for all common forms of hyperthyroidism including Graves’ disease.

Option C, elevated TSH with a low free T4. Think this through. Low free T4, lower total body cellular energy release. Low circulating free T4, the anterior lobe of the pituitary, will release more TSH to encourage more free T4 release from the thyroid. So why did the free T4 remain low? The thyroid has failed. And this of course is the clinical laboratory presentation of hypothyroidism. And if hypothyroidism was the correct answer, the patient would have hyporeflexia, constipation, dry skin, fatigue, and the like. 

Option D, normal limit TSH with a low free T4. One more time, think this through. If the TSH was within normal limits, then with a functioning thyroid, the free T4 would be within normal limits. This is in the day-to-day something that is physiologically impossible and that's not going to show up on the boards. 

Key takeaway: The majority of time if you think through the pathophysiology of a disease then the anticipated clinical presentation and confirmatory laboratory testing simply falls into place.

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