The utility of IGF1 in the evaluation of pediatric patients with endogenous hypercortisolemia.

BACKGROUND: Cushing Disease (CD) is a rare endocrine disorder associated with impaired growth hormone (GH) and short stature. Insulin-like growth factor-1 (IGF-1) is a marker of GH secretion. METHODS: Patients with young onset CD (<21 years old) and available IGF-1 levels at diagnosis and/or follow-up were studied (total = 194, diagnosis = 174, follow-up = 104). IGF-1 was reported as z-score (IGF1z). RESULTS: IGF1z was lower than expected in the general population (median IGF1z: -0.92 [-1.54, 0.07], p < 0.0001) at diagnosis and remained low at follow-up (median: -1.13 [-1.78, -0.66], p < 0.0001). There was no correlation of IGF1z at diagnosis with BMI; there was a weak correlation with height (rs = 0.19, p = 0.035). IGF1z was inversely correlated with markers of hypercortisolemia, including morning (rs = -0.31, p < 0.0001) and midnight cortisol (rs = -0.30, p < 0.0001), and with insulin resistance (Homeostatic Model Assessment for Insulin Resistance, HOMA-IR, rs = -0.27, p < 0.01). CONCLUSIONS: IGF-1 levels in CS are on the lower side of the normal range during active disease and remain low at one year after treatment. IGF-1 levels correlated mainly with markers of hypercortisolemia rather than the short stature of patients and should not be used in the assessment of growth in this population. IMPACT: We report that IGF-1 levels in childhood during active hypercortisolemia and up to 1 year after resolution are on the lower side of the normal range. Our results demonstrate that IGF-1 levels during active hypercortisolemia correlate mainly with markers of Cushing syndrome. This report adds data to the current literature where reports of IGF-1 in Cushing syndrome have shown variable results. Understanding the lack of utility of IGF-1 in assessing growth parameters in the pediatric Cushing syndrome population is important for physicians caring for these patients who should not use IGF-1 for diagnostic or treatment decisions.