Growth Hormone and Prolactin Secretion after External Cranial Irradiation for Extrasellar Tumours

Deficiency of one or more anterior pituitary hormones may follow treatment with external radiation when hypothalamo-pituitary axis lies within the field of radiation. Patients with brain tumours who are treated with radiation frequently have growth hormone (GH) deficiency, other neuro-endocrine abnormalities are presumed to be uncommon. The present study has been undertaken with the aim to study GH and prolactin secretion, their relationship with dose of radiotherapy and duration after radiotherapy in patients who have received extracranial radiation for extrasellar tumours.

In this study, 96 patients who underwent cranial radiation before 12 months, were evaluated. Basal 8 a.m. venous blood samples were taken for estimation of prolactin and GH. Insulin tolerance test was performed for stimulated GH levels.

GH deficiency was present in 59% patients. Isolated GH deficiency was present in 12 (21%) cases, whereas others had associated hormone deficiency. Height percentiles of prepubertal and pubertal patients were 10(th) to 25(th) (-1.5 to -0.5SD). Patients with isolated GH deficiency had received significantly higher radiation dose than normal pituitary function (5795 ± 24 vs 4908 ± 71, p=0.001). Proportion of patients with GH deficiency increased with increasing dose of radiation (p=0.12), fractional dose of radiation (p=0.08) and increasing duration after radiotherapy (p=0.038). GH levels among all decreased significantly with increasing dose of radiation (p=0.02). Hyperprolactinemia was present in 21% of cases. GH deficiency is more common with lower (<5ng/ml) and higher (>15ng/ml) prolactin levels.

GH deficiency is common after extracranial radiation for extrasellar tumours. GH deficiency is related to dose of radiation, fraction of radiation, and duration after radiotherapy. All prepubertal and pubertal patients with GH deficiency had their height percentile within normal range. Relation of prolactin and GH deficiency indicates that radiation affects both hypothalamus and pituitary.