[Congenital hypothyroidism with probable anomaly of thyroid receptiveness to thyrotropin. 2 cases]

Congenital hypothyroidism associated with unresponsiveness to thyrotropin (TSH) is a very rare condition. In the two cases reported the thyroid gland was not enlarged and endogenous THS secretion control was normal: the high TSH levels observed during hypothyroidism returned to normal after thyroid hormone replacement therapy and were normally responsive to TRH stimulation. Thyroid iodide clearance was investigated under various conditions of stimulation and inhibition. In hypothyroidism clearance was normal and TSH levels very high. During replacement therapy clearance seemed to be inversely correlated to levels of circulating thyroid hormones; it was almost nil in euthyroidism. Whatever the level of circulating hormones, clearance was not reactivated by exogenous TSH. In one patient in euthyroidism clearance, which was virtually zero, was unmodified after butyric AMPc stimulation, which suggests that the anomaly lies below the AMPc stage.