Familial Partial Target Organ Resistance to Thyroid Hormones

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.