Thyroid function in acromegaly before and after transsphenoidal hypophysectomy followed by cryoapplication.

Thyroid function was studied in acromegaly before and after transsphenoidal hypophysectomy followed by cryoapplication. The clinical material comprised 36 euthyroid, 1 hypothyroid and 3 hyperthyroid patients. In addition to the usual thyroid parameters a standard thyrotrophin-releasing hormone (TRH) stimulation test using 200 mug of synthetic TRH given iv was used. In untreated acromegaly with euthyroidism the response of serum TSH to TRH was significantly less than in normal controls, the increment being 7.1 mU/1 vs. 12.5 mU/1. In 23% of the patients the response was subnormal (less than 3.0 mU/1). The total thyroxine was significantly higher than in controls. Goitre occurred in 53% of the patients. After operation 3 patients became hypothyroid. In 30% of the patients remaining euthyroid the response to TRH was subnormal and the mean response in this group was close to the lower normal limit of 3.0 mU/1. In 7 patients who showed a subnormal response to TRH before or shortly after the operation there was a gradual increase and normalization of the response during the next few years. A subnormal, and also a low normal response to TRH before or after hypophysectomy does not necessarily indicate an increased risk for the development of hypothyroidism, and indeed the pituitary remnant seems to have a remarkable capacity for regeneration. In the hypothyroid patient there was a low normal response to TRH, the reason being unknown. In one of the hyperthyroid patients the basal TSH level was 6.5 and 8.9 mU/1 on two occasions in the thyrotoxic phase, showing a small response to TRH. The possibility that hyperthyroidism was due to increased secretion of TSH is discussed but not claimed proven. The incidence of hyperthyroidism in a large material of acromegaly from this department equals 9% which is above the prevalence of hyperthyroidism in the general population in Finland, indicating that acromegaly in one way or another seems to increase the incidence of manifest thyrotoxicosis.