Lesson 4: Causes of Hyperthyroidism
In this lesson students will learn about the various disorders that can cause hyperthyroidism, including Graves' disease, solitary or multiple nodules, thyroiditis, adenomas, excess iodine ingestion, genetic mutations and resistance to thyroid hormone.
Topics include:
Graves' disease
Thyroid nodules
Thyroiditis
Toxic adenoma
Iodine-rich products
Genetic mutations
Resistance to Thyroid Hormone
Discussion topics
Introduction
Hyperthyroidism has a number of different distinct causes. Hyperthyroidism may also be a transient mild condition or a limited chronic disorder lasting many years.
Thyrotoxicosis, the condition of thyroid hormone excess, also has several different causes, including the ingestion of excess thyroid hormone. In this lesson students will learn about the various disorders or events that lead to hyperthyroidism and thyrotoxicosis. Students will also learn about the clinical significance of these disorders.
Overall, Graves’ disease, which is an autoimmune disorder, is the most common cause of hyperthyroidism. Graves’ disease accounts for approximately seventy percent of all instances of hyperthyroidism, and it affects about seven times as many women as men. While any excess of thyroid hormone can cause eye signs and symptoms, several different autoimmune syndromes, such as congestive thyroid eye disease, pretibial myxedema, vitiligo and acropachy, can accompany Graves’ disease. Patients with Graves’ disease typically have disease courses in which periods of hyperthyroidism alternate with periods of remission, often over many years.
Other causes of hyperthyroidism include thyroid nodules; toxic adenoma; postpartum thyroiditis; subacute or viral thyroiditis; which is also known as De Quervain’s thyroiditis; bacterial or suppurative thyroiditis; ingestion of food or dietary supplements contaminated with thyroid hormone or excess iodine; tumors that cause excess TSH or hCG production; and several distinct genetic mutations including resistance to thyroid hormone.
Thyroid nodules that trap excess iodine and produce excess thyroid hormone are referred to as toxic or hot. When multiple nodules contribute to hyperthyroidism, the patient is diagnosed as having a condition of toxic multinodular goiter or TMG. TMG, which is also known as Plummer’s disease, is more likely to occur in patients older than 45 years.
In this lesson, students will learn about the basic differences between the various causes of hyperthyroidism. In addition, students will learn what sets these different disorders apart, that is, how the disorders can be distinguished from one another. Students will also learn how individuals can have two or more co-existing conditions that contribute to their hyperthyroid condition. For instance, while rare, patients with Graves’ disease may also have thyroid nodules that produce excess thyroid hormone and contribute to hyperthyroidism. This condition is sometimes called Marine-Lenhart syndrome.
It’s important to know the definitive cause of hyperthyroidism and the tests that are used to accomplish this. In this section we’ll focus on some of these tools, and later, in chapter 6, we’ll elaborate on the different diagnostic tools that are available. Different types of hyperthyroidism can follow quite different disease courses and require different treatment. For instance, subacute thyroiditis resolves on its within 6-8 weeks, followed by a period of transient hypothyroidism. Most cases of Graves’ have an initial hypothyroid phase and resolve after 12-18 months on anti-thyroid meds or alternative medical treatment.
Treatment for Graves’ disease is very different than treatment for the inflammatory condition of thyroiditis. In Graves’ disease, treatments that lower thyroid hormone production are used. In thyroiditis anti-inflammatory medicines, pain medications or rarely antibiotics may be used.
Furthermore, in patients with resistance to thyroid hormone or RTH, laboratory results have different meanings. This occurs because the body’s tissues respond differently to thyroid hormone in patients with RTH. Knowing the definitive cause of hyperthyroidism is important for ensuring optimal treatment and an optimal treatment response.
