Endocrine Abstracts

External Beam Radiation is frequently used in the management of Head and Neck Cancer, including parathyroid cancer. The thyroid may also be exposed to radiation during mantle radiotherapy for Hodgkin’s disease and breast cancer. Radiation can result in thyroid dysfunction in a high proportion of individuals with an intact thyroid prior to radiation. Primary hypothyroidism is the most common finding, in around 30% of patients, with a peak onset at around 2-3 years post treatment. Incidence may be increasing over time, possibly as a result of better recognition or longer survival. Hypothyroidism is most commonly diagnosed based on abnormal thyroid function tests rather than symptoms. Higher radiation doses to the thyroid are associated with higher risk. Less frequently, an acute thyroiditis can occur with transient thyrotoxicosis and more rapid progression to hypothyroidism. Older series report a risk of hyperthyroidism due to Grave’ disease after mantle cell radiotherapy for Hodgkin’s disease. In contrast the rate of hypothyroidism after treatment of breast cancer was low. Those with hyperthyroidism require close observation, with beta blockade as required, and prompt initiation of levothyroxine on progression to hypothyroidism. Amongst those with de novo hypothyroidism, sub-clinical hypothyroidism may occur first, but the risk of progression to clinically overt hypothyroidism is high. Finally, radiotherapy for nasopharyngeal tumours may include the pituitary and carry a risk of secondary hypothyroidism.