Conventional pituitary irradiation in acromegaly. Effect on growth hormone and TSH secretion

Thirty-one patients who had been treated for acromegaly for 1-21 years with conventional pituitary irradiation were re-examined. Immunoreactive growth hormone (GH) was measured in connection with an oral glucose load. Adrenal and gonadal functions were assessed on the basis of plasma cortisol and the urinary excretion of 17-ketogenic steroids, 17-ketosteroids and gonadotrophins. In evaluating the thyroid-pituitary axis the thyrotrophin-releasing hormone stimulation test (TRH) was used. Initially 30 patients had experienced definite benefit from the treatment but at the time of re-examination 10 still had clinically active disease and required another type of treatment. Normal GH levels (less than 5 ng/ml/1) were seen in only 12 patients. Skin thickness was normal in 15 out of 30. Thus the remission rate can be evaluated as being 67% as regards clinical activity, 50% with regard to skin thickness and 39% in terms of GH levels. Hypogonadism occurred in 12 patients (39%) and adrenal and thyroid failure in 5 patients each (16%). The response to TRH was within the normal range in 2 of the hypothyroid patients. In 22 euthyroid patients the mean increment in serum TSH in response to 200 mug of synthetic TRH was only 5.8 mU/1 which was significantly below the normal mean 12.5 mU/1. Furthermore, in 7 of these patients (32%) the response was absent or subnormal (less than 3.0 mU/1). This indicated that the pituitary is capable of secreting enough TSH for maintenance of an euthyroid state but that its capacity is limited. Conventional pituitary irradiation is not a very effective treatment in acromegaly but may still be recommended in selected cases.