A 26-year-old male athlete undergoes an independent medical evaluation required for a specialized life insurance policy. He reports feeling exceptionally well and currently runs approximately per week. His family history is notable for a younger brother diagnosed with attention-deficit/hyperactivity disorder, but there is no known history of autoimmune or endocrine diseases.
Vital signs include a heart rate of and a blood pressure of . Physical examination reveals a normal-sized, non-tender thyroid gland without palpable nodules. There is no evidence of proptosis, lid lag, hyperreflexia, or resting tremor.
Laboratory studies demonstrate:
| Parameter | Patient Value | Reference Range |
|---|---|---|
| Thyroid-stimulating hormone (TSH) | ||
| Free thyroxine (T4) | ||
| Free triiodothyronine (T3) |
An MRI of the brain with gadolinium contrast demonstrates a normal pituitary gland without sellar or suprasellar masses.
Which of the following is the most likely underlying mechanism for this patient's laboratory abnormalities?
- Mutation in the gene encoding the thyroid hormone receptorAnswer
- BMonoclonal proliferation of anterior pituitary thyrotrope cells
- CProduction of autoantibodies directed against thyroid peroxidase
- DImmunoglobulin-mediated activation of the thyrotropin receptor
- ESurreptitious ingestion of synthetic exogenous levothyroxine