SUN-592 Goiters and Levothyroxine Do Not Always Mix

Introduction Levothyroxine suppression therapy used to be the standard of care in the prevention of thyroid nodule and goiter growth. It has been found to be associated with complications in patients who are biochemically euthyroid. The practice remains widespread among practitioners despite recommendations against it from the ATA. Clinical Case A 74 year old female with a recently diagnosed goiter presented to the neurology intensive care unit as a transfer from an outside hospital for a cerebrovascular accident. Endocrinology was consulted for a suppressed TSH in the setting of new onset atrial fibrillation. About three months prior, she was referred by her primary care provider to see an endocrinologist for an asymptomatic goiter. Her TSH at the time was 2.376 uIU/mL (0.450-5.330 uIU/mL). The endocrinologist prescribed levothyroxine 150 mcg daily in an attempt to shrink the thyroid. Her levothyroxine dose was reduced to 125 mcg daily one month later after she was found to have TSH of 0.018 uIU/mL and FT4 of 2.4 ng/dL (0.71-1.85 ng/dL). Immediately prior to her admission to the hospital, she developed shortness of breath, aphasia, and right sided weakness. Her TSH was 0.086 uIU/mL and FT4 was 1.70 ng/dL on admission. At the time of the consult, the patient weighed 50 kg and her exam was notable for irregularly irregular tachycardia, aphasia, right sided weakness, and a large goiter. A diagnosis of iatrogenic hyperthyroidism was made. Her thyroid function tests normalized after a short course of methimazole for several days. The atrial fibrillation stabilized and her symptoms improved. She was eventually discharged to a rehabilitation facility. Conclusion Since TSH is a known growth factor for thyroid tissue, it has been postulated that suppressing TSH secretion may cause the stabilization as well as the shrinkage of thyroid nodules and goiters(2). Concern regarding the safety of this practice developed as studies demonstrated an association with increased rates of arrhythmias and bone weakening(2). The ATA now recommends against routine TSH suppression for benign thyroid nodules in iodine sufficient populations(2). Despite these concerns, Bonnema et al showed that a large cohort of endocrinologists still prescribed levothyroxine suppression therapy when provided with an index case of a non-toxic nodular goiter(1). This case highlights the dangers of levothyroxine suppression therapy for the shrinkage of thyroid nodules and goiters. References 1. Bonnema SJ et al (2002). Management of the nontoxic multinodular goiter: a North American survey. The Journal of Clinical Endocrinology and Metabolism 87 (1): 112-117. 2. Haugen BR et al (2016). 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid 26 (1): 1-133.