Cushing's syndrome and bone mineral density: Lowest Z scores in young patients

Background: Patients with Cushing's syndrome have a high prevalence of osteoporotic fractures. Little is known about factors determining bone mineral density (BMD) in these patients. Objective: To evaluate which factors influence BMD at the time of diagnosis of Cushing's syndrome. Methods: In 77 consecutive patients with Cushing's syndrome with a median age of 41.1(interquartile range 31.1 to 52.2) years we measured BMD of the lumbar spine and the femoral neck at the time of diagnosis. From the medical records we obtained information on possible predictors of BMD. We compared BMD with a reference population by means of the Z score. Adjustment for other variables than age and sex was made with linear regression models. Results: Patients with Cushing's syndrome had a low Z score in both the lumbar spine (-1.07 SD (95% CI -1.43 to -0.71 SD)) and in the femoral neck (-0.81 SD (95% CI -1.06 to -0.55 SD)). 82% of patients had osteopenia at one or both sites (T score lower than -1 SD), including 31% with osteoporosis (T score -2.5 SD or lower). The main determinant of the Z score at both sites and for both sexes was age. Z score increased by about 0.4 SD per decade. 81% of patients <40 years had osteopenia at one or both sites, including 31% with osteoporosis. For patients ≥40 years these percentages were 83 and 32%, respectively. Origin of Cushing's syndrome, average 24-hour serum cortisol, duration of symptomatic glucocorticoid excess, sex, body mass index, menstrual status and duration of amenorrhoea did not influence the Z score. Conclusions: At the time of diagnosis, BMD in patients with Cushing's syndrome is low compared with sex- and age-matched controls. The prevalence of osteopenia and osteoporosis at the time of diagnosis of Cushing's syndrome is independent of age. Treatment with bisphosphonates should be considered in patients of all ages with Cushing's syndrome who have a decreased BMD.