American Board of Pathology (ABPath) Practice Test 2025 - Free Pathology Exam Practice Questions and Study Guide

Hyperthyroidism is most typically caused by a localized nodule or adenoma that overproduces hormones. This is often seen in cases such as toxic adenomas or multinodular goiter, where one or more areas of the thyroid gland become hyperactive, leading to increased synthesis and release of thyroid hormones, particularly thyroxine (T4) and triiodothyronine (T3).

In these cases, the excess hormone production can lead to symptoms associated with hyperthyroidism, including weight loss, increased heart rate, anxiety, and heat intolerance. The mechanism involves proliferative changes in the thyroid tissue that result in an abnormal increase in hormone production independent of the regulatory mechanisms typically controlled by the pituitary gland.

The other options describe conditions that do not typically lead directly to hyperthyroidism: hypothalamic dysfunction could lead to abnormal thyroid-stimulating hormone (TSH) release, autoimmune destruction of thyroid tissue is associated more with hypothyroidism (as in Hashimoto's thyroiditis), and iodine deficiency usually results in hypothyroidism rather than hyperthyroidism due to insufficient hormone production.