Serum Markers of Bone and Collagen Turnover in Patients with Cushing’s Syndrome and in Subjects with Adrenal Incidentalomas

The aim of this study was to assess serum levels of some markers of bone turnover and collagen synthesis in 22 patients with adrenal incidentalomas (AI), a model of silent glucocorticoid excess, and to compare the results with those obtained in 18 patients with Cushing's syndrome (CS). Osteocalcin (BGP), bone isoenzyme of alkaline phsophatase, carboxy-terminal propeptide of type I procollagen, and carboxy-terminal cross-linked telopeptide of type I collagen were measured as biochemical indexes of bone turnover, and amino-terminal propeptide of type III procollagen was determined as an index of collagen synthesis. Two groups of healthy volunteers evenly matched for sex, age, and menstrual status were used for a case-control analysis of AI and CS groups, respectively. Patients with AI showed a slight, albeit significant, reduction in serum BGP and a mild increase in carboxy-terminal cross-linked telopeptide of type I collagen levels compared with controls [median, 6.6 vs. 7.8 ng/mL (P < 0.05) and 4.2 vs. 3.1 micrograms/L (P < 0.01), respectively]. No significant differences were found when comparing the other markers. Patients with CS had BGP, bone isoenzyme of alkaline phosphatase, and amino-terminal propeptide of type III procollagen levels significantly lower than control values [median, 3.0 vs. 7.3 ng/mL (P < 0.0001); 4.4 vs. 11.5 micrograms/L (P < 0.01); 2.2 vs. 4.3 micrograms/L (P < 0.0001), respectively], but no significant difference in the other markers. These results confirm a clear inhibition of osteoblastic activity in CS and could suggest an enhanced bone metabolism in patients with AI. The degree of impairment of bone turnover in patients with AI does not seem enough to recommend surgery (removal of the adrenal adenoma) in the absence of other indications.