Hypothyroidism in head and neck cancer patients: experimental and clinical observations

Damage to the thyroid gland may occur in patients undergoing treatment for head and neck neoplasms. This injury may result from damage incurred during surgery, from radiation therapy, or a combination of the two. Development of hypothyroidism is often insidious with potential harmful effects. An experimental study was performed to study the effects of hypothyroidism in pigs whose skin closely approximates that of the human. Wound tensile strength and flap necrosis were studied in the hypothyroid animal treated by surgery, radiation, and a combination of the two. The results of this study indicate that hypothyroidism alone has no significant unfavorable impact on wound tensile strengths or flap survival. When combined with preoperative radiation, however, there are statistically significant deleterious effects on both wound tensile strengths and flap survival. Histologically, collagen fibers within the wound appear shorter and thinner, which probably accounts for decreased wound tensile strengths. A clinical review of 62 head and neck cancer patients was also conducted. Within the study group, 10% of patients developed abnormally low thyroxine measurements, whereas 15% developed high thyroid-stimulating hormone levels as the only evidence of early primary hypothyroidism. Hypothyroidism was not statistically related to tumor size, nodal status, clinical staging, or treatment group (surgery alone, radiation alone, or combination surgery and radiation). A previously unreported finding is that patients who develop a second primary tumor are significantly at risk for developing hypothyroidism. All patients diagnosed with a head and neck cancer should undergo baseline thyroid function testing, including measurement of TSH, and have serial repeat testing after treatment. Thyroid function determination should be mandatory in patients undergoing oncologic salvage procedures or treatment of a second primary tumor.