TBS predicts fracture risk in subclinical hypercortisolism
MedWire News: Trabecular bone structure (TBS) may be a better predictor for fracture risk than bone mineral density (BMD) in patients with subclinical hypercortisolism (SH), Italian researchers report.
Iacopo Chiodini (University of Milan) and colleagues explain that, as with overt cortisol excess, patients with SH have an increased risk for fracture independent of BMD. This increased risk may be due to reduced bone quality, which can be measured by TBS.
To investigate, Chiodini and team measured BMD and TBS in 102 patients (62% women) with adrenal incidentaloma (AI), a condition known to be associated with SH.
Dual-energy X-ray absorptiometry (DXA) showed that AI patients with SH (n=34) had significantly lower BMD at the lumbar spine (LS), femoral neck, and total hip than AI patients without SH (n=68), and controls without AI or SH (n=70). BMD did not differ significantly between AI patients without SH and controls, however.
TBS, also measured by DXA, was significantly lower in SH-positive patients than in SH-negative patients and controls, and was also significantly lower in SH-negative patients than in controls.
In addition, TBS was significantly inversely correlated with serum cortisol after adjustment for age, LS BMD, body mass index (BMI), and gender.
The prevalence of vertebral fractures was significantly higher among patients with SH than among those without it, at 31% versus 28%.
Furthermore, patients with low TBS (Z-score <-1.5) were 4.8 times more likely to have a fracture than those with normal TBS (Z-score ≥-1.5), after adjustment for age, gender, and BMI. Low TBS combined with low LS BMD (Z-score <0) also predicted fracture at an odds ratio of 4.37, but low LS BMD alone was not independently associated with fracture prevalence.
The researchers calculated that low TBS alone had the best sensitivity for predicting fractures, at 81.4%, while low TBS combined with low LS BMD had the best specificity, at 79%. Normal TBS combined with normal LS BMD had the highest specificity for excluding fractures, at 88.1%
A small follow-up study among 40 of the patients showed that each Z-score unit decreased in baseline TBS was significantly associated with a 11.2-fold increased likelihood for a new fracture at 24 months regardless of LS BMD, BMI, and age.
"These findings suggest that, in the management of SH-positive patients, it is important to measure TBS and that combining the information derived from TBS and LS BMD is helpful for identifying patients to be screened for vertebral fractures."
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By Laura Cowen