Evaluation of adrenal function in patients with growth hormone deficiency and hypothalamic–pituitary disorders: comparison between insulin-induced hypoglycemia, low-dose ACTH, standard ACTH and CRH stimulation tests

Abstract

Objectives: Patients with organic growth hormone deficiency (GHD) or with structural hypothalamic–pituitary abnormalities may have additional anterior pituitary hormone deficits, and are at risk of developing complete or partial corticotropin (ACTH) deficiency. Evaluation of the integrity of the hypothalamic–pituitary–adrenal axis (HPA) is essential in these patients because, although clinically asymptomatic, their HPA cannot appropriately react to stressful stimuli with potentially life-threatening consequences. Design and methods: In this study we evaluated the integrity of the HPA in 24 patients (age 4.2–31 years at the time of the study) with an established diagnosis of GHD and compared the reliability of the insulin tolerance test (ITT), short synacthen test (SST), low-dose SST (LDSST), and corticotropin releasing hormone (CRH) test in the diagnosis of adrenal insufficiency. Results: At a cortisol cut-off for a normal response of 550 nmol/l (20 μg/dl), the response to ITT was subnormal in 11 subjects, 6 with congenital and 5 with acquired GHD. Four patients had overt adrenal insufficiency, with morning cortisol concentrations ranging between 66.2–135.2 nmol/l (2.4–4.9 μg/dl) and typical clinical symptoms and laboratory findings. In all these patients, a subnormal cortisol response to ITT was confirmed by LDSST and by CRH tests. SST failed to identify one of the patients as adrenal insufficient. In the seven asymptomatic patients with a subnormal cortisol response to ITT, the diagnosis of adrenal insufficiency was confirmed in one by LDSST, in none by SST, and in five by CRH tests. The five patients with a normal cortisol response to ITT exhibited a normal response also after LDSST and SST. Only two of them had a normal response after a CRH test. In the seven patients with asymptomatic adrenal insufficiency mean morning cortisol concentration was significantly higher than in the patients with overt adrenal insufficiency. ITT was contraindicated in eight patients, and none of them had clinical symptoms of overt adrenal insufficiency. One of these patients had a subnormal cortisol response to LDSST, SST, and CRH, and three exhibited a subnormal response to CRH but normal responses to LDSST and to SST. Conclusion: We conclude that none of these tests can be considered completely reliable for establishing or excluding the presence of secondary or tertiary adrenal insufficiency. Consequently, clinical judgment remains one of the most important issues for deciding which patients need assessment or re–assessment of adrenal function.