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

Which thyroid disorder involves one or more nodules in a multinodular goiter becoming TSH-independent, without exophthalmos or pretibial myxedema?

1. Follicular carcinoma

2. Riedel thyroiditis

3. Thyroid storm

4. Toxic multinodular goiter

The correct answer is: Toxic multinodular goiter

Toxic multinodular goiter is a condition where one or more nodules within a multinodular goiter become autonomous. This means that these nodules can produce thyroid hormones independently of thyroid-stimulating hormone (TSH) regulation. In this disorder, the hyperfunctional nodules lead to excess production of thyroid hormones, which can result in symptoms of hyperthyroidism. In terms of the hallmark signs, unlike conditions such as Graves' disease—which typically presents with symptoms like exophthalmos and pretibial myxedema—toxic multinodular goiter does not usually exhibit these features. This differentiates it from autoimmune hyperthyroidism, where eye involvement and skin manifestations are more common. The presence of one or more hyperfunctioning nodules leads to increased levels of thyroid hormones, potentially causing a clinical state of hyperthyroidism, but the condition remains distinct by lacking the autoimmune characteristics observed in other forms of hyperthyroidism. This clinical picture aligns well with the specific features described in the question.