Hypothyroidism after radiotherapy for patients with head and neck cancer

We report on 2 cases of hypothyroidism presenting clinical symptoms that occurred after radiotherapy for cancer of the head and neck and on the results of estimating thyroid function in patients with head and neck cancer who received radiotherapy. The first patient underwent total laryngectomy for laryngeal cancer without sacrificing the thyroid gland and partial gastrectomy for gastric cancer. Radiotherapy of the neck was carried out postoperatively. Two years later, the patient developed chest pain; pericardial effusion was detected, leading to a diagnosis of myxedema caused by hypothyroidism. The second patient received radiotherapy alone for laryngeal cancer. Two months later, low serum sodium concentration and anemia were detected in this patient. The cause of these changes was subsequently found to be hypothyroidism. Based on our experience with these 2 cases, we measured thyroid function in 35 patients who had undergone neck radiation for head and neck cancer at our hospital over the past 10 years. Hypothyroidism was observed in 13 of the 35 patients (37%). The prevalence of hypothyroidism was 46% (6/13) for patients treated with both radiation and surgery, as compared with 32% (7/22) for those who received radiation alone. The risk factors responsible for hypothyroidism were not evident from the statistical analysis of these cases. We believe that thyroid function should be evaluated periodically in patients who have undergone neck radiation because it is often difficult to diagnose hypothyroidism only from clinical symptoms.