Total body calcium measurements using neutron-activation analysis in Cushing's syndrome

Summary

Total body calcium content (TBCa) was estimated byin vivo neutron activation analysis in 16 patients (14 female, 2 male) with active Cushing's syndrome, pituitary driven in all but two cases. Apart from being nonreproductive, patients were unselected. TBCa was below the predicted young normal value in all patients (mean±SD, 85.2±5.8% of predicted,P<0.01 vs. predicted) and in 13 of the 16 patients, was also below the predicted value when allowance was made for expected postmenopausal skeletal losses (mean±SD, 92.7±12.5% of predicted,P<0.02). However, individual values of TBCa were significantly lower (P≤0.05) than the predicted normal range, corrected for postmenopausal losses, in only 3 patients (19% of the group). Initial TBCa apparently was not related to duration of the disease or to current urinary-free cortisol levels. At presentation, radiographic signs of significant osteoporosis (multiple vertebral and/or rib fractures) were present in four patients, three of whom had subnormal or borderline TBCa compared with the young normal predicted range. TBCa measurements were repeated in 9 patients 1–10 years after successful treatment, and were generally unchanged. During this period, only one vertebral fracture (consistent with simple postmenopausal osteoporosis) appeared in these patients. We conclude that bone mass tends to be low in newly diagnosed Cushing's syndrome, but that significant reduction beyond expected postmenopausal losses is relatively uncommon. Successful treatment prevents new fractures without increasing TBCa, suggesting that bone connective tissue can be restored without remineralization.