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The hypothalamus-pituitary function after pituitary stereotactic radiosurgery: evaluation of growth hormone
M Degerblad1, K Brismar, T Rähn
1Department of Endocrinology and Diabetology, Karolinska Hospital, Stockholm, Sweden. Marie.Degerblad@molmed.ki.se
Objectives:
Radiation therapy to the pituitary gland means a considerable risk of developing hypopituitarism. The aim of the study was to investigate the growth hormone releasing hormone (GHRH)-growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis after treatment with stereotactic radiosurgery to the pituitary because of Cushing's disease.
Setting:
Inpatient ward in university clinic.
Subjects:
Eleven adult patients (eight women, three men), 20-65 years of age were studied 2.5-11.3 years after stereotactic radiosurgery (isocentre dose 50-100 Gy lesion-1) and compared with healthy controls.
Main Outcome Measures:
Spontaneous GH secretion was evaluated as 12-h night GH profiles. Stimulated GH responses were evaluated in seven of 11 patients using arginine-insulin and GHRH tests. Serum IGF-I levels were measured in fasting serum morning samples.
Results:
All patients except one displayed blunted nocturnal GH profiles. After arginine-insulin challenge, six of seven patients displayed low GH release. GH response was higher after GHRH injection compared with both the response to arginine-insulin and to the maximum GH levels in the nocturnal profiles. Seven patients had an IGF-I standard deviation score (SDS) within the normal range for age. Serum IGF-I values were correlated to mean GH values in the 12-h night profile (r = 0.67, P < 0.05) and both these variables were negatively correlated to time elapse since last radiation treatment (r = -0.64, P < 0.05 and r = -0.78, P < 0.05, respectively).
Conclusions:
Our patients with Cushing's disease evaluated several years after stereotactic radiosurgery as the primary and only treatment, demonstrated severely blunted spontaneous GH secretion and GH response to arginine-insulin. A disturbed regulation at the hypothalamic level was suggested as mechanism for this. Noteworthy is that serum IGF-I values correlated to the mean values of the 12-h GH profile.