Abstract
A clinically euthyroid 2-yr-old girl was found to have a diffuse goiter that measured 3 × 5.5 cm with a prominent systolic bruit. Serum free T 4 (3.4 ng/dl) and serum T 3 (360 ng/dl) remained elevated for the next 10 months even though she remained clinically euthyroid. Elevation of serum free T 4 (3.0 ng/dl) and serum T 3 (265 ng/dl) was also present in the 24-yr-old nongoitrous mother who had symptoms and signs of hypothyroidism. Following intravenous injection of TRH, basal TSH levels of 2.7 and 2.8 μU/ml increased to peak values of 17 and 21 μU/ml at 30 min in the daughter and mother, respectively. Administration of exogenous T 3 followed by sequential testing with boluses of TRH revealed retention of TSH responsiveness in both daughter and mother during pretreatment with dosage regimens of T 3 below 125 μg daily. Maintenance of TSH responsiveness to TRH in the presence of elevated levels of serum free T 4 and serum T 3 indicates relative pituitary insensitivity to thyroid hormone which could be overridden by increasing the circulating levels of serum T 3 three to fivefold over the already elevated basal levels. The absence of clinical signs of thyrotoxicosis indicates peripheral insensitivity to thyroid hormone with elevated circulating concentrations presumptively compensating for the defect. Resistance to thyroid hormone in two generations of the same family suggests genetic inheritance, and is concordant with four earlier reports of familial aggregation in this syndrome.
Published Version
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