MON-609 Hormonal Outcomes after Partial Thyroidectomy: The Cleveland Clinic Experience

Background: Partial thyroidectomies (PT) are done frequently, yet controversy remains about thyroid hormonal outcomes. A large number of patients are also being started on thyroid hormone replacement (THR) immediately post PT. In this study, we examine the Cleveland Clinic (CC) data to provide insight to these questions. Methods: Patients with PT performed at CC between 2000-2010 were included. Baseline variables and thyroid hormone levels/replacement for 5 years post PT were collected. Those with unexplained thyrotoxicosis, lost to follow up in the 1(st) year, or with completion thyroidectomy/RAI in follow up were excluded. Patients were classified based on hormonal outcome: overt hypothyroidism (OH, TSH >10 uU/mL or TSH >4.2 uU/mL started on THR), subclinical hypothyroidism (SH, TSH >4.2-10 uU/mL with no THR), euthyroid (Eu, TSH 0.4-4.2 uU/mL with no THR). A separate cohort of patients had immediate start on THR with some developing suppressed TSH (<0.4 uU/mL). Patients were followed for up to 5 years (longer if patient was Eu). Results: There were 380 patients with average age at surgery 51 years old, 77.4% female, and median follow up 58.4 months. Of these, 244 were not immediately started on THR. In this group, 73 developed OH (29.9%), 29 SH (11.9%), 142 stayed Eu (58.2%). Another 115 patients were immediately started on THR. Compared with OH patients, Eu patients had larger weight adjusted remaining gland (cc(3)/weight in kg, p 0.015), were less likely to have lymphocytic infiltrate (p 0.021) and had lower TSH (1.1 [0.84,1.6] vs 1.9 [1.5,2.3], p <0.001). Positive antibody status, family history of thyroid disorders, radiation history were similar between the 3 cohorts. In the SH group, 48.1% of patients normalized their TSH <4.2 in follow up (final TSH 3.4 [2.2,3.7]). For those patients immediately started on THR, 58 (50.4%) suppressed. The starting weight adjusted THR dose strongly correlated with suppression (no sup 1.03±0.41 vs sup 1.39±0.39, p <0.001) as did having a family history of thyroid disorders (p 0.036). ROC revealed THR with LT4 >1.1 mcg/kg/day were more likely to suppress (PPV 0.69, NPV 0.81). Discussion: Our study demonstrates that for those not immediately started on THR, a majority will remain Eu and that lower pre-op TSH and absence of lymphocytic thyroiditis on pathology make it more likely to be Eu. Importantly, for those patients trying to avoid TRH, our study shows many patients with SH can return to Eu status on follow up. In practice, a large number of patients are being started immediately on THR after PT. If clinicians choose immediately start THR, which our study would conclude is not needed, we suggest an initial weight based dose below 1.1 mcg/kg/day.