USMLE (United States Medical Licensing Examination) Step 1 Practice Exam 2025 - Free USMLE Step 1 Practice Questions and Study Guide

Decreased serum TSH (thyroid-stimulating hormone) levels generally indicate an elevated level of thyroid hormones, primarily T3 (triiodothyronine) and T4 (thyroxine). One significant consequence of elevated thyroid hormones is acute thyrotoxicosis, a condition characterized by the overactivity of the thyroid gland, leading to symptoms such as rapid heartbeat, weight loss, increased appetite, nervousness, and excessive sweating. In this context, acute thyrotoxicosis can occur when there is a surge of thyroid hormones, which causes feedback to the pituitary gland to suppress TSH production.

On the other hand, conditions such as Hashimoto thyroiditis are associated with increased TSH levels due to hypothyroidism resulting from autoimmune destruction of the thyroid. Lymphocytic hypophysitis, primarily seen in pregnant women, affects pituitary function and may not be directly related to the thyroid hormone levels. Subacute granulomatous thyroiditis, often arising after a viral infection, typically presents with an initial hyperthyroid phase followed by hypothyroidism, and does not consistently correlate with decreased TSH levels.

Therefore, the connection between decreased serum TSH levels and acute thyrotoxicosis is crucial