Diagnosis and Management of the Autonomously Functioning Thyroid Nodule: The Walter Reed Army Medical Center Experience, 1975-1996

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Abstract
In order to characterize the clinical and laboratory features of autonomously functioning thyroid nodules (AFTNs), and to assess optimal diagnosis and management of patients with this disorder, we performed a retrospective analysis of 49 such patients over a 22-year period encompassing January 1975 to November 1996. The following data were analyzed: thyroid hormone levels, thyroid scintiscan, radioiodine uptake, fine-needle aspiration biopsy, triiodothyronine (T3) suppression testing, thyrotropin-releasing hormone (TRH) stimulation test, and thyroid ultrasound. Clinical outcomes assessed included persistent hyperthyroidism, hypothyroidism, and nodule shrinkage after treatment, or in patients followed without definitive therapy, nodule growth, spontaneous degeneration, and progression to hyperthyroidism. Biochemical hyperthyroidism, often subclinical, was found in 73.5% of patients at presentation and in an additional 24.4% of patients during subsequent follow-up. The introduction of sensitive thyrotropin (TSH) testing during the period of study resulted in a decrease in the use of the T3-suppression test and TRH stimulation test from 100% and 20%, respectively, in the period from 1976-1980, to 4% each in the period from 1991-1996. T3-thyrotoxicosis occurred in 12.2% of patients. Thyrotoxicosis at any time during the course of follow-up was positively correlated with nodule size at diagnosis. Definitive therapy, used in 42.8% of patients, consisted of radioiodine ablation (38.1%) or thyroidectomy (61.9%). No patient had recurrence of thyrotoxicosis after definitive therapy, but 25% became hypothyroid. During follow-up for a mean of 30.9 months, nodules enlarged in 25% of patients overall, or 33% of patients not receiving definitive therapy. Cystic degeneration was documented in 26.5% of patients, although this change rarely reversed subclinical hyperthyroidism. The diagnosis of an AFTN requires a demonstration of TSH-independent nodular hyperfunction. The introduction of sensitive TSH assays has simplified the evaluation of AFTN patients and revealed a high prevalence of subclinical thyroid hyperfunction in this disorder. In view of current increased awareness of adverse consequences associated with subclinical hyperthyroidism and the rarity of spontaneous resolution of hyperthyroidism in AFTN patients (despite a propensity for spontaneous hemorrhage), definitive therapy is recommended. Both radioiodine and hemithyroidectomy have high cure rates and a low posttreatment incidence of hypothyroidism.