USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which of the following statements is true regarding toxic multinodular goiter?

1. Associated with exophthalmos

2. Commonly occurs in children

3. Characterized by dependence on TSH

4. One or more nodules become TSH-independent

The correct answer is: One or more nodules become TSH-independent

The statement that one or more nodules in a toxic multinodular goiter become TSH-independent is accurate and reflects the pathology of this condition. In toxic multinodular goiter, which is often associated with prolonged iodine deficiency or long-standing goiter, certain nodules typically develop mutations that allow them to grow and function autonomously from regulatory signals such as Thyroid-Stimulating Hormone (TSH). This autonomy leads to the production of excess thyroid hormones, causing hyperthyroidism symptoms. As a consequence, the TSH-independent nodules can supervise their own hormone production without the need for stimulation from TSH, which is normally produced by the pituitary gland. This characteristic is key in differentiating toxic multinodular goiter from other forms of thyroid dysfunction, such as Graves' disease, where the entire gland is stimulated by TSH due to autoimmune mechanisms. In contrast, the other statements are not representative of the typical features of toxic multinodular goiter. For example, exophthalmos is more closely associated with Graves' disease rather than toxic multinodular goiter. Also, this condition primarily affects older adults rather than children, and in terms of TSH dependence, while the nodules initially respond to TSH,