Familial Partial Target Organ Resistance to Thyroid Hormones

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Abstract
A 30-year old woman with a history of recurrent goiter, who had undergone two partial thyroidectomies, is described. She presented with tachycardia, nervousness and a fine tremor of the fingers. Initially, she had normal serum thyroid hormone levels: thyroxine (T4 (D)) 11.6 μg/100 ml, triiodothyronine (T3) 138 ng/100 ml, normal levels of binding proteins and a very high serum thyrotropin (TSH), 98 μU/ml During follow-up T4 (D) increased to 17.2 μg/100 ml, T3 increased to 277 ng/100 ml, while TSH decreased to 11 μU/ml. There was an exaggerated response of TSH to a peak value of 550 μU/ml after intravenous administration of 200 μg thyrotropin-releasing hormone (TRH). Administration of 60 mg prednisolone daily resulted in a blunting of the response to TRH. Administration of 50 μg T3 daily for 1 month resulted in a fall in serum TSH from 98 to 50 μU/ml. Later, when the serum TSH level had fallen spontaneously to 20 μU/ml, administration of 100 μg T3 daily for two weeks resulted in a fall in serum TSH to 5.3 μU/ml. Treatment with 20 mg carbimazole daily for 3 weeks resulted in a decrease in serum T4 levels with a concomitant increase of serum TSH. There was no evidence of pituitary enlargement and other pituitary hormone levels were normal. All the relatives studied (father, sister, three children) had elevated T4 levels with normal basal TSH values. It is concluded from this study that our patient presents evidence of partial resistance to thyroid hormones.