Which condition presents with elevated T3 but normal T4 (T3 thyrotoxicosis)?

Which condition presents with elevated T3 but normal T4 (T3 thyrotoxicosis)?

• A. T3 thyrotoxicosis
• B. Graves' disease
• C. Toxic multinodular goiter
• D. Subacute thyroiditis

Answer: (A)

This question tests recognizing a pattern where thyroid hormone excess is driven mainly by T3 rather than T4. In T3 thyrotoxicosis, the circulating level of free T3 is elevated while free T4 remains normal. This happens when T3 is produced in excess or generated more from peripheral conversion of T4, so T3 becomes the predominant active hormone driving symptoms. Clinically, you’d see thyrotoxicosis with suppressed TSH, but if you only look at T4 you might miss the diagnosis unless free T3 is measured. Other common causes of thyrotoxicosis, like Graves’ disease, toxic multinodular goiter, or subacute thyroiditis, typically raise both T3 and T4 (though T3 can be relatively higher in some cases), so they don’t fit the described isolated T3 elevation as cleanly. The best match for elevated T3 with a normal T4 is T3 thyrotoxicosis.

This question tests recognizing a pattern where thyroid hormone excess is driven mainly by T3 rather than T4. In T3 thyrotoxicosis, the circulating level of free T3 is elevated while free T4 remains normal. This happens when T3 is produced in excess or generated more from peripheral conversion of T4, so T3 becomes the predominant active hormone driving symptoms. Clinically, you’d see thyrotoxicosis with suppressed TSH, but if you only look at T4 you might miss the diagnosis unless free T3 is measured. Other common causes of thyrotoxicosis, like Graves’ disease, toxic multinodular goiter, or subacute thyroiditis, typically raise both T3 and T4 (though T3 can be relatively higher in some cases), so they don’t fit the described isolated T3 elevation as cleanly. The best match for elevated T3 with a normal T4 is T3 thyrotoxicosis.