THE FUNCTION OF THE PITUITARY‐THYROIDAL AXIS IN ACROMEGALIC PATIENTS V. PATIENTS WITH HYPERPROLACTINAEMIA AND A PITUITARY TUMOUR

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Abstract
SUMMARY: The function of the pituitary‐thyroidal axis was examined in fifty‐three of sixty‐two patients with hyperprolactinaemia and a pituitary tumour and in forty of forty‐four acromegalic patients, in whom one or more indices of the pituitary‐thyroid function were determined before treatment. In the patients with hyperprolactinaemia and a pituitary tumour, sellar + extrasellar tissue (EST) size showed a significant negative correlation with the response of TSH to TRH (ΔTSH) as well as with the circulating T4 and T3 levels. These correlations were not present in the acromegalic patients. In the prolactinoma group a sharp decrease in mean serum T4 and T3 levels was found at sellar + EST sizes exceeding 3 cm2. In twenty‐three patients with a sellar + EST size of 3 cm2 or more, thirteen (57%) showed a T4 level of less than 6 μg/dl against none of twenty‐eight patients with a sellar + EST size of less than 3 cm2. For T3, using a limit of 120 ng/dl, the corresponding numbers were eight out of thirteen (62%) and none of ten patients respectively. A positive correlation was observed between ΔTSH and the T3 levels but not between ΔTSH and T4, while in the acromegalic patients there was no correlation between TSH reserve and T3 or T4. In the patients with hyperprolactinaemia and a pituitary tumour positive correlations between basal TSH and ΔTSH as well as between T4 and T3 levels were observed. These correlations were not found in the acromegalic patients.In conclusion: (1) Thyroid function appears to be independent of pituitary tumour size in patients with acromegaly but not in patients with hyperprolactinaemia and a pituitary tumour. (2) In acromegalic patients the high incidence of an impaired TSH response (without hypothyroidism and independent of tumour size) may be caused by suppression of TSH secretion rather than by destruction of thyrotrophic cells.