Insulin Hypoglycemia Test and Releasing Hormone (Corticotropin-Releasing Hormone and Growth Hormone-Releasing Hormone) Stimulation in Patients with Pituitary Failure of Different Origin

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Abstract
To investigate the efficacy of endocrine evaluation in diagnosing and localizing the cause of anterior pituitary failure, 17 patients with suprasellar space-occupying lesions, 4 patients with intrasellar tumors, 8 patients with no detectable anatomical lesion, 1 patient with posttraumatic failure and 1 patient with septooptical dysplasia were investigated. Endocrine evaluation consisted of measuring adrenocorticotropic hormone (ACTH), cortisol, and growth hormone (GH) levels during insulin hypoglycemia test (IHT) and after administration of corticotropin-releasing hormone (CRH) and growth hormone-releasing hormone (GRH). In addition, basal prolactin levels, gonadal and thyroid function were evaluated. The results showed that 4 of 17 patients with suprasellar tumors had normal ACTH and GH responses during IHT and after releasing hormone (RH) administration. Five of these patients had a normal ACTH or cortisol rise but no GH response during IHT. All 5 had a normal ACTH and 3 had normal GH rise after RH. Seven patients with suprasellar tumors had no ACTH or GH response during IHT, but all had an ACTH response to CRH. Only 3 of this group had a GH response to GRH. There was one exception of a patient who showed a GH and ACTH rise during IHT but only a blunted ACTH and no GH rise after RH administration. Four patients with pituitary failure and no demonstrable lesion had an ACTH rise after CRH but no GH rise after GRH, whereas in 3 patients with isolated ACTH deficiency no ACTH rise after CRH was seen. In 4 patients with nonsecreting pituitary tumors normal ACTH responses to IHT and CRH were seen, whereas GH rose during IHT only in 1 patient. Thirteen of all patients had elevated prolactin levels above 500 µU/ml. Eight of these patients had ACTH and GH secretion patterns compatible with a hypothalamic defect, i.e. no response during IHT but an ACTH or GH response or both after RH administration. However, 5 patients with a bonafide pituitary tumor and nonresponsiveness to the releasing hormone had also elevated prolactin levels. In 2 patients with moderate hyper-prolactinemia, ACTH and GH responses to IHT and RH were completely normal. Our findings show that the endocrine function tests used in this study are not always reliable in locating the hypothalamo-pituitary defect.