Dr. Daniell points out that direct injury to the pituitary and hypothalamus after treatment for nasopharyngeal carcinoma is another cause of hypothyroidism after head and neck radiation therapy. This is an important addition to our discussion, and would not be identified by an elevation in thyroid-stimulating hormone (TSH).
An increase in TSH was used as our definition of hypothyroidism because our patient population did not include individuals with nasopharyngeal carcinoma. As such, the radiation dose received by the pituitary or hypothalamus was minimal. Nonetheless, it is important to note that patients with nasopharyngeal carcinoma will require more than a TSH determination when followed for late, radiation-induced hypothyroidism.