Familial inappropriate TSH secretion: evidence suggesting a dissociated pituitary resistance to T3 and T4.

The study of pituitary thyroid relationships of a 40-year-old woman, suffering from recurrent goiter, is presented. The characteristics of this case were the following: i) constant hyperthyrotropinemia (range 8.2 to 29 micro u/ml) despite high thyroid hormone levels (mean total T4:13.4 microgram/dl; mean total T3:255 ng/dl) and clinical euthyroidism; ii) this TSH hypersecretion is not regulated by an excess of T4, while a suppressive effect is easily observed with T3. Together with the clinical effects observed with administration of T3 and T4, this suggests that thyroid hormone resistance predominates at the pituitary level, for T4 while not T3; iii) evidence is presented for the familial distribution of the trait and its mode of transmission. The clinical aspect and the pattern of resistance exhibited by the propositus and her progeny appear distinct from those of previous observations of thyroid hormone resistance.