PITUITARY IRRADIATION IS INEFFECTIVE IN NORMALIZING PLASMA INSULIN-LIKE-GROWTH-FACTOR-I IN PATIENTS WITH ACROMEGALY

Pituitary irradiation suppresses GH hypersecretion in patients with ac romegaly. Within 10 yr after radiotherapy, up to 80% of patients achie ve plasma GH levels below 5 mu g/L. Whether this is sufficient to norm alize plasma insulin-like growth factor I(IGF-I) levels, is unknown. W e examined the effect of radiotherapy on plasma IGF-I concentrations i n patients with acromegaly. We reviewed hospital charts of 140 patient s with acromegaly seen in our institution between 1975 and 1996. Data on plasma GH and IGF-I were extracted and tabulated longitudinally tog ether with the information about the concomitant medical therapy. We i ncluded data from the patients who received radiotherapy as a part of their treatment and whose IGF-I was monitored for more than 1 yr after ward. To avoid the potential bias, the data for patients who were refe rred to us for medical therapy, having failed radiation elsewhere, wer e excluded. A total of 38 datasets were submitted for the final analys is. The average follow-up was 6.8 +/- 0.8 yr (range, 1-19). Only 2 pat ients achieved age-and sex-adjusted normal IGF-I levels while off medi cal therapy. Noncured patients had a mean plasma GK level of 4.6 +/- 1 .1 mu g/L but still elevated plasma IGF-I levels (219 +/- 26% of the u pper normal limit) at the last follow-up visit. A random GH concentrat ion below 1.5 mu g/L was associated with a pathologically high plasma IGF-I concentration in 43% of instances. Radiotherapy appears to be in effective in normalizing plasma IGF-I levels in acromegaly. A multicen ter study to reevaluate the future use of this modality in patients wi th acromegaly is warranted.