Research Day

Forgotten But Not Gone: Hyperthyroidism In A Patient With Prior Total Thyroidectomy

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BACKGROUND: Forgotten goiters, or mediastinal thyroid tissue discovered years after total thyroidectomy, are exceptionally rare occurrences; one study of 3,044 patients with prior total thyroidectomy identified only 10 instances of goiter recurrence over a 25-year period. Forgotten goiters are typically non-functional, and present with symptoms of mass effect in patients maintained euthyroid through the use of thyroid hormone replacement. The anti-arrhythmic amiodarone is known to alter thyroid dynamics in 32% of treated patients, with 3% of patients developing amiodarone induced thyrotoxicosis (AIT). A subset of those patients demonstrates AIT type 1; endogenous thyroid hormone production from an abnormal gland upon exposure to amiodarone (an example of the Jod-Basedow phenomenon).

CASE HISTORY: An 81-year-old man with remote history of "total thyroidectomy", chronically treated with levothyroxine, presented to his primary care physician. He had recently been hospitalized with atrial flutter for which he had DC cardioversion and was discharged on amiodarone. Five years earlier, a substernal paratracheal mass was identified as minimally functioning thyroid tissue. At the time of his current appointment the patient was found to be hyperthyroid. Subsequent follow up labs demonstrated continued increases in free thyroxine levels despite discontinuation of his levothyroxine. This suggested new, autonomous function of his mediastinal thyroid mass.

DISCUSSION: This case highlights a rare occurrence of activation of a "forgotten goiter". A clinically non-functional mass, with over 15 years of regular thyroid function monitoring, which gained autonomous function upon exposure to amiodarone, subsequently converting the previously euthyroid (on replacement hormone) patient to a hyperthyroid state.

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