Lesson 5: Diagnosing Hyperthyroidism
In this lesson students will learn to recognize the laboratory, imaging and biopsy tests used to help diagnose hyperthyroidism and its specific cause.
Topics include:
Disorders that can mimic hyperthyroidism
Thyroid function tests
Obsolete laboratory tests
Thyroid antibody tests
Imaging tests
The radioiodine uptake and scan
Fine needle aspiration biopsy
Topics for Discussion
Introduction
As we learned in the previous lesson, it’s important to determine the exact cause of hyperthyroid disorders. In this lesson course participants are introduced to the various laboratory tests and imaging procedures used to diagnose hyperthyroidism and determine its specific cause. Students are also introduced to other disorders that can mimic hyperthyroidism and confuse diagnosis.
To accurately diagnose hyperthyroidism, the patient’s clinical symptoms and signs must be evaluated along with test results. With this approach physicians are able to form a complete clinical picture and make a proper diagnosis. Laboratory results alone can indicate that disease is likely but when patients are asymptomatic, that is, they have no symptoms of disease, the results should be questioned or repeated at a later time.
While thyroid laboratory tests have an accuracy rate greater than 99 percent, there are other conditions that can cause similar results or affect thyroid function test results. Furthermore, some patients have rare thyroid antibodies or heterophile antibodies that falsely increase or falsely lower their test results.
This lesson includes descriptions of the primary laboratory tests used to screen for and diagnose hyperthyroidism and also the blood tests used to determine if the patient has an autoimmune hyperthyroid disease. Course participants will learn the underlying principle behind specific laboratory tests, they’ll learn what tests are optimal, and they’ll learn about the various sources of error in laboratory medicine.
Imaging tests, including the radioiodine uptake and scan and the thyroid ultrasound, are also described in this section and their limitations are detailed. In addition, students are introduced to the different imaging patterns seen on the scans of patients with different hyperthyroid disorders. The fine needle aspiration biopsy is also described, and its uses and limitations are discussed.
While imaging tests are often used for the purpose of differentiating cold and hot nodules, the results can be erroneous or misleading. There are many gray areas because thyroid tissue that takes up more iodine may be blocked from taking up iodine during the scan. This can make a hot nodule appear cold. While most nodules are benign, nodules that are cold are much more likely to be malignant. A fine needle aspiration biopsy is necessary to determine the type of cells that make up the nodule. This tells if the nodule is malignant or benign.
The importance of tracking laboratory and imaging test results is emphasized in this lesson. Ideally, patients would keep copies of all lab results, indicating what medications they were on and how they felt when their labs were drawn. This can help in determining what thyroid hormone levels are optimal for the individual.
Because all of the treatments for hyperthyroidism have the potential to cause hypothyroidism, and hypothyroidism can lead to a poor treatment outcome, thyroid patients are shown how to make sure they’re receiving optimal treatment and are not being moved into hypothyroidism. When treatments that cause permanent hypothyroidism are used, it’s important to monitor thyroid hormone levels frequently since levels typically fluctuate for the first year, affecting therapy needs.
In autoimmune thyroid disease, it’s important to avoid treatments that cause hypothyroidism. As a homeostatic mechanism, in hypothyroidism thyroid cells increase their activity in an effort to produce more thyroid hormone. This increased activity also causes increased antibody production and a worsening of the original autoimmune disorder.
