ESPE Abstracts

Background: The hypothalamic-pituitary-adrenal (HPA) axis is vital for stress response and homeostasis. Central adrenal insufficiency (CAI) results from inadequate adrenocorticotropin (ACTH) secretion due to hypothalamic or pituitary disorders, leading to insufficient adrenal cortisol production. CAI manifests in nonspecific symptoms and can cause life-threatening adrenal crises. Diagnostic delays are common due to the nonspecific symptoms, making accurate and timely diagnosis crucial.

Aim: This study aim ed to evaluate the effectiveness of the Insulin Tolerance Test (ITT) in predicting or confirming CAI and compare these results with the Synacthen (ACTH Stimulation) test.

Methods: A retrospective analysis was conducted on 390 patients at risk for ACTH deficiency, seen at the Late Effect Clinic from January 2010 to January 2024. Sixteen patients who underwent both ITT and Synacthen tests within 90 days were included. The study stratified patients by age, gender, diagnosis, and test outcomes, with a cortisol cut-off level of 477 nmol/L used for both tests.

Results: The 16 patients consisted of 9 males and 7 females, with a mean age at ITT of 11.86 years and a median age of 12.55 years. Oncological diagnoses included Medulloblastoma (n = 7), Parameningeal rhabdomyosarcoma (n = 2), and a variety of other rare brain tumours. Endocrine diagnoses comprised Growth Hormone Deficiency (GHD), Hypopituitarism, and Diabetes Insipidus, among others. Test results indicated mean basal and maximum cortisol levels, GH response, glucose levels, and intervals between ITT and subsequent Synacthen testing. Our cohort showed that 56% of patients (n = 9) underwent the high Synacthen (250 microgram) dose, while 31% of patients (n = 5) underwent the low Synacthen (1 microgram) dose, with 13% of patients (n = 2) having no test sheet in their chart. Outcome comparison revealed that 87.5% of patients (n = 14) failed the ITT, while 81.3% of patients (n = 13) passed the Synacthen test. Only three patients (18.8%) failed both the ITT and Synacthen tests, while two patients (12.5%) passed both tests. This highlights discrepancies between the two methodologies in identifying central adrenal insufficiency.

Conclusion: Our study demonstrates that the Synacthen test is superior to the ITT for confirming HPA axis insufficiency. While ITT is a cost-effective tool for initially ruling out the majority of CAI cases, its limitations in diagnosing the condition necessitate follow-up with the more reliable Synacthen test. Therefore, ITT can be effectively utilized as an initial screening method, but a confirmatory low- or high-dose Synacthen test should be considered in cases with more borderline cortisol responses (> 400 and < 477).