Abnormally high TSH in subject with thyrotoxicosis affected by congenital hypothyroidism. Case report

Inappropriate secretion of TSH (IST) refers to a heterogeneous group of syndromes in which patients show unsuppressed TSH levels in spite of high serum free thyroid hormone concentrations. It has been recognised that IST can be due to both thyroid hormone resistance (RTH) and pituitary TSH-secreting tumours. The former can be generalised (GRTH) or pituitary (PRTH) if the resistance is more severe in the pituitary than in the rest of the tissues. This case report points out the persistence of this patient's TSH resistance to the inhibition of high concentrations of circulating thyroid hormones with clear symptoms of thyrotoxicosis even after many years of replacement therapy; it also suggests that in this case FT4 is the parameter to evaluate the therapy's effectiveness.