Poster Presentation The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2017

Elevated insulin like growth factor 1 in cushings disease (#211)

Katherine English 1 , Viral Chikani 1 , Goce Dimeski 2 , Warrick Inder 1
  1. Department of Diabetes and Endocrinology, Princess Alexandra Hospital, Brisbane, Queensland, Australia
  2. Pathology Queensland, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia

Introduction: Growth hormone (GH) secreted from pituitary somatotrophs leads to insulin-like growth factor-1 (IGF-1) production mainly in hepatocytes. Studies have shown sustained hypercortisolism decreases GH secretion, with variable serum IGF-1 levels reported.  The objective of this study was to investigate the relationship between serum IGF-1 in patients with untreated CD compared to matched controls and to assess for changes in pre-(untreated) and post-pituitary surgery (remission) IGF-1 levels in patients with CD.

Methods: Twenty-three cases of CD were matched to controls (19 women, 4 men) for tumour size, age, BMI, diabetes, gonadal status and IGF-1 levels measured within 1 year (on the same assay) to account for potential assay drift.  Pre- and >3 months post-pituitary surgery serum IGF-1 was available for comparison for twelve CD patients.

Results: IGF-1 levels in CD were significantly higher than controls (30 nmol/L vs. 23 nmol/L, P=0.004), despite matching for factors known to affect IGF-1 levels (age, tumour diameter and BMI, P=0.66, P=0.15 and P=0.43 respectively).  Eight of 23 (35%) untreated cases and one of 23 (4%) matched controls had elevated IGF-1 levels above an age-matched reference range, with six cases and no controls having IGF-1 levels >1.1 times the upper limit of normal (ULN). The proportion of patients with elevated serum IGF-1, above and >1.1 ULN was higher in cases compared to controls, (McNemar’s test for paired proportions P=0.02 and P=0.03, respectively).  Pre- vs post-operative serum IGF-1 (collected 16 months IQR 14 to 22 apart) in twelve CD patients was decreased (32 nmol/L vs 27 nmol/L, P=0.003), despite no difference in pre- vs post-operative pituitary hormone dysfunction (P=0.3). 

Conclusion: Patients with untreated CD may have elevated IGF-1 levels, which appear to decrease when in remission post-operatively. While the exact mechanism remains unclear, it is unlikely to be due to relative GH hypersecretion.