ORIGINAL ARTICLE Predictors of thyroxine replacement following hemithyroidectomy in a south east Asian cohort Peng Ng MBBS 1 | Cheryl Ho MBBS 1 | Wee Boon Tan FRCS 2 | Kee Yuan Ngiam FRCS 2 | Chwee Ming Lim FRCS ENT 3 | Kwok Seng Thomas Loh FRCS ENT 3 | Min En Nga MRCPath 4 | Rajeev Parameswaran FRCS 2 1 Yong Loo Lin School of Medicine, National University of Singapore, Singapore 2 Department of Endocrine Surgery, National University Hospital, Singapore 3 Department of Otolaryngology, National University Hospital, Singapore 4 Department of Pathology, National University Hospital, Singapore Correspondence Rajeev Parameswaran, Department of Endocrine Surgery, National University Hospital, Lower Kent Ridge Road, Singapore 119074. Email: rajeev_parameswaran@nuhs.edu.sg Abstract Background: Thyroxine replacement following a hemithyroidectomy is not com- monly discussed during consent for the procedure as the risk of hypothyroidism is perceived to be low. Methods: Retrospective review of 901 patients who underwent hemithyroidectomy at a tertiary referral institution during the period January 2000 to December 2015. The main outcome studied was the overall incidence of hypothyroidism and the associated risk factors. Results: Hypothyroidism developed in 123 (13%) patients and 94 patients (10%) required hormone supplementation over a mean follow up of 21 months (range 1-168 months). Preoperative TSH of more than 2.5 was seen in 38 of 123 (31%) of patients. Presence of diffuse thyroiditis was the only independent risk factor on multivariate analysis (P = 0.002) found to be associated with the development of hypothyroidism. Conclusion: After thyroid lobectomy, approximately one in 10 patients requiring thyroid hormone treatment for hypothyroidism. Presence of diffuse thyroiditis is a significant risk factor for hypothyroidism. KEYWORDS hemithyroidectomy, hypothyroidism, thyroiditis 1 | INTRODUCTION Hemithyroidectomy is a commonly performed procedure for thyroid nodules of various aetiologies. The AACE guide- lines published in 2010 recommend hemithyroidectomy as a treatment for unilateral benign nodular disease, 1 follicular neoplasms, and patient choice. 2,3 There is also some evi- dence to prescribe hemithyroidectomy for malignancies smaller than 4 cm, solitary intrathyroidal malignancy in low risk patients. 2,4–6 The advantage of a thyroid hemithyroidect- omy is that it eliminates the risk of permanent hypocalcae- mia and bilateral recurrent laryngeal nerve palsies. 7–9 Hemithyroidectomy has also the added advantage of leav- ing the functioning contralateral lobe untouched so that the patients affected will not have to take replacement thyroxine. It is believed that hypothyroidism is less likely following a hemi- thyroidectomy; however, thyroxine supplementation is required in about 10%-50% of patients. 10–13 The reported incidence of hypothyroidism varies in the literature and this variation is due to a variety of factors such as definition of hypothyroidism, population differences, surgical techniques, follow-up, and tim- ing of thyroxine supplementation. 12 Therefore, it is important to evaluate the factors responsi- ble for developing hypothyroidism in patients undergoing a hemithyroidectomy. Obtaining this information will be useful for surgeons to counsel patients on the actual risk of developing hypothyroidism, the dosage of thyroxine supple- mentation, and duration of follow up. The aim of the study Received: 5 April 2018 Revised: 25 September 2018 Accepted: 5 December 2018 DOI: 10.1002/hed.25592 Head & Neck. 2018;1–5. wileyonlinelibrary.com/journal/hed © 2018 Wiley Periodicals, Inc. 1