Lack of a Threshold Size for Autonomously Functioning Thyroid Nodules that Excludes Hyperthyroidism

Abstract

Objective: To correlate the size of autonomously functioning thyroid nodules (AFTNs) with thyroid function tests. Methods: A retrospective analysis was performed of data from patients with a diagnosis of a single AFTN who were seen in a university-based endocrinology clinic between January 1, 2003, and December 31, 2015. Patients with a nuclear thyroid scan confirming the presence of an AFTN without significant cystic degeneration were included in the study. Results: The volume of the AFTN and the corresponding thyroid function tests were compared in 32 patients who met inclusion criteria. There was no correlation between the volume of the AFTN and thyroid-stimulating hormone (TSH) levels (r2 = 0.044). There was also no volume threshold below which an AFTN was always associated with a TSH within the reference range. Conclusion: The results agree with the findings of other recent studies comparing the volume of AFTNs with TSH levels, suggesting that smaller nodules can still demonstrate subclinical and overt hyperthyroidism and that a normal TSH level does not preclude the presence of an AFTN. Abbreviations: AFTN = autonomously functioning thyroid nodule; T3 = triiodothyronine; T4 = thyroxine; TSH = thyroid-stimulating hormone.