Excessive Thyrotropin Response to Thyrotropin-releasing Hormone in Pseudohypoparathyroidism

摘要

Extract: In 8 of 10 patients with pseudohypoparathyroidism, confirmed by increased immunoreactive plasma parathyroid hormone concentrations and/or defective urinary excretion of adenosine 3′,5′-monophosphate (cAMP) after parathyroid extract infusion, excessive plasma thyrotropin (thyroid-stimulating hormone) (TSH) response to thyrotropin-releasing hormone (TRH) injection was found. On the other hand, in all seven cases with idiopathic true hypoparathyroidism the TSH response was normal. In two of three patients with pseudopseudohypoparathyroidism, with normal or slightly low plasma calcium, normal or slightly high immunoreactive plasma parathyroid hormone concentration, and intermediate response of cAMP to parathyroid extract, the TSH response to TRH was increased. The results indicate that moderate primary hypothyroidism is frequently present in pseudohypoparathyroidism. Thyroid dysfunction may only be detectable with the use of TSH stimulation by TRH, since clinical signs and other studies of thyroid function did not definitely suggest hypothyroidism in our patients. The rise of TSH is suppressible by thyroxine treatment, but is not influenced by vitamin D treatment. The TSH response to TRH is significantly correlated with the decrease of tubular reabsorption of phosphate after parathyroid extract infusion in patients with pseudo- and pseudopseudohypoparathyroidism.Speculation: TSH stimulation by TRH may be a useful test for the further delineation of biochemical variants of pseudohypoparathyroidism.