PITUITARY RESISTANCE TO THYROID-HORMONES

Pituitary thyroid hormone resistance (PRTH) refers to a particular for m of thyroid hormone refractoriness that is accompanied by peripheral hyperthyroidism, as only the TSH-secreting pituitary cells appear to b e resistant to the effects of thyroid hormones. The presence of PRTH i s suspected and diagnosed on the basis of the finding of high free thy roid hormone levels along with unsuppressed TSH, clinical signs and sy mptoms of hyperthyroidism and values of at least one of the parameters evaluating peripheral thyroid hormone action in the hyperthyroid rang e. However, most patients with PRTH present with clinical signs and sy mptoms of thyroid dysfunction, particularly goiter and tachycardia, ov erlapping those recorded in patients with generalized thyroid hormone resistance (GRTH), i.e. refractoriness to thyroid hormones at both pit uitary and peripheral tissue level. Moreover, most of them display nor mal values of other parameters evaluating the peripheral effects of th yroid hormones and bear mutations in the gene encoding for T3 nuclear receptors similar to those found in patients with GRTH. These findings are questioning the existence of PRTH as a separate clinical entity a nd support the view that the various forms of thyroid hormone resistan ce may be part of a spectrum of disease with variable expression in di fferent issues.