| Abstract: | Thyrotropic function was studied in 100 patients with hypothalamic or pituitary tumours before treatment. Eighteen patients with thyroid deficiency showed no signs of primary hypothyroidism. This was also showed in 4 other hypothyroid patients who had pituitary tumours studied later on. Only 4 of these 22 patients had TSH deficiency. The other 18 had normal or high plasma TSH levels, and the TSH response to TRH was normal but often delayed and/or prolonged. This pattern, suggestive of secretion of TSH with reduced biological activity, might however be due to other factors. Tumoral invasion of the hypothalamus, present in these 18 cases, could reduce secretion of TRH and dopamine. Hypothyroidism would then be secondary to TRH deficiency if TRH is considered to have a direct thyroid-stimulating action, and, like dopamine deficiency, could contribute to maintaining normal or high TSH secretion. |
