The role of Zulewski's clinical score in screening for hypothyroidism in post-radiation therapy nasopharyngeal carcinoma patients

Background: Nasopharyngeal carcinoma (NPC) is a leading cause of cancer related death in Asia; and the fourth most common malignancy in Indonesia. Hypothyroidism is one of the most commonly overlooked radiotherapy -induced late side effect due to its gradual occurrence despite its irreversibility. Unfortunately, thyroid evaluation is not widely accessible throughout Indonesia. Therefore, it is quite important to utilize a simple and reliable surrogate tool for hypothyroidism screening. This study aims to evaluate thyroid function and to validate Zulewski's scoring system as a temporary surrogate marker for hypothyroidism in post-RT NPC patients. Method: This is a cross-sectional study involving NPC patients between November 2015 and March 2016 at Dr. Cipto Mangunkusumo General Hospital, Jakarta, Indonesia. The patients had completed radiation therapy (RT) within the preceding six months. They were evaluated for signs and symptoms of hypothyroidism with Zulewski's clinical scoring system and with serological analysis of thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels. Results: There were 97 patients in this study. 28 (28.9%) subjects experienced hypothyroidism based on the TSH and FT4 levels, with subclinical hypothyroidism (13.4%) as the most common type, followed by overt hypothyroidism (9.3%) and hypothyroxinemia (6.2%). From the subjects with hypothyroidism, 19.6% had Zulewski's clinical score <5, while 40.5% had scores >= 5. Subjects with <5 Zulewski's clinical score exhibited signs and symptoms more related to the NPC itself, while those who scored >= 5 showed signs and symptoms more closely related to hypothyroidism. Conclusion: This study shows that hypothyroidism is commonly exhibited in NPC patients after radiotherapy (28.9%). Zulewski's clinical score of >= 5 indicates signs and symptoms more closely related to hypothyroidism.