Characterization of the metabolic phenotypes of Cushing's syndrome and growth hormone deficiency: a study of body composition and energy metabolism

OBJECTIVE: A comparison of the severity and distribution of perturbations in body composition and their relationship to energy metabolism in glucocorticoid excess and GH deficiency (GHD) has not been undertaken before. The aim of this study was to investigate the impact of Cushing's syndrome (CS) and GHD on whole and regional body composition and energy metabolism. DESIGN: Cross-sectional study design. PATIENTS: Eighteen subjects with CS (12 women, aged = 41.5 +/- 3.0 years, 24-h urinary free cortisol = 1601 +/- 361 nmol/day, normal < 300 nmol/day), 22 subjects with GHD (14 women, age = 42.9 +/- 2.9 years) and 18 normal subjects (11 women, age = 46.8 +/- 2.8 years). MEASUREMENTS: Lean body mass (LBM), fat mass (FM) and regional body composition were assessed by dual-energy X-ray absorptiometry (DEXA). Resting energy expenditure (REE) and fat oxidation (Fox) were assessed by indirect calorimetry. RESULTS: Mean percentage FM was significantly greater by 30% in CS (P = 0.002) and 22% in GH-deficient subjects (P = 0.014) than in normal subjects. LBM was significantly lower by 15% in CS (P = 0.002) and 11% in GHD (P = 0.013). In CS, the proportion of lean tissue in the limbs was 12% less than in normal (P = 0.001) and GH-deficient subjects (P = 0.0005). Truncal fat represented a greater proportion of total FM in CS (52.5 +/- 1.8%vs. 46.9 +/- 1.3%, P = 0.014) than in normal subjects, but not in GHD. REE and Fox, corrected for LBM, were significantly lower in GHD (P < 0.02 for both vs. normal) but not in CS. CONCLUSION: FM was higher and LBM lower in both CS and GHD. However, there is a greater abnormality of regional body composition in patients with CS who exhibit a lower limb lean mass and a greater truncal fat. Reduced REE and Fox contribute to increased adiposity in GHD. As REE and Fox are not perturbed in CS, other mechanisms must explain the marked gain in truncal and total fat.