Thyroid dysfunction after radiation therapy in head and neck cancer patients

INTRODUCTION: The reported incidence of hypothyroidism following surgery and/or radiation therapy for head and neck cancer varies widely. Most patients undergo thyroid lobectomy during laryngectomy. Standard radiation treatment portals often include the thyroid gland. The insidious development of hypothyroidism may be misdiagnosed. This study examines the incidence of thyroid dysfunction in the setting of head and neck cancer therapy. MATERIALS AND METHODS: Thyroid function tests were performed on 100 consecutive patients treated in the head and neck tumor clinic. Statistical inferences on proportions were made using chi-square analysis. RESULTS: Therapy included surgery only (10 patients), radiation therapy only (28 patients), and combined therapy (62 patients). These patients experienced thyroid dysfunction in 0%, 29%, and 45% of individuals respectively. These differences were statistically significant (P < .05). The highest rate of dysfunction (69%) was associated with patients undergoing laryngectomy and radiation therapy. When laryngectomy was not performed, thyroid dysfunction occurred in 28%. CONCLUSION: The likelihood of thyroid dysfunction after radiation therapy is high particularly when combined with surgery in which thyroid lobectomy is performed and the contralateral lobe is potentially devascularized. These results suggest that radiation therapy is a primary factor in alteration of thyroid function. We recommend that routine thyroid function testing be part of follow-up of all head and neck cancer patients.