RETURN TO ABSTRACT LISTING


Objective:
Lung transplant candidates routinely undergo bone mineral density (BMD) screening using dual-energy X-ray absorptiometry (DXA) due to increased risk of osteoporosis and related fractures secondary to comorbidities and prolonged immunosuppression. Nonetheless, postoperative fractures have been demonstrated, even in patients with normal BMD. Trabecular Bone Score (TBS) has emerged as a complementary index of bone microarchitecture and independent predictor of fracture risk that has been seldom studied in this population. The present study sought to investigate the value of TBS, in conjunction with DXA, for the evaluation of osteoporosis in lung transplant candidates.

Materials and Methods:
A retrospective review of 191 DXA scans of patients undergoing lung transplantation at a large, urban, academic medical center was performed. The mean age of the sample was 62.0 (SD = 9.7), with a modest male predominance (61.8%) and relatively diverse racial/ethnic composition (46.3% Hispanic, 29.4% white, 21.9% black). TBS was calculated using DXA images of the lumbar spine. Patients were classified by BMD and microarchitectural integrity using established T-score cutoffs for DXA and TBS, respectively. Paired t-test was used to compare differences in mean T-scores between DXA and TBS. Exact McNemar’s tests were used to compare the proportion of patients meeting the criteria for osteopenia, osteoporosis, partially degraded bone, and degraded bone.

Results:
Differences in the observed rates of osteopenia (36.6%), osteoporosis (11.0%), partially degraded bone (38.7%), and degraded bone (33.5%) were statistically significant, p < 0.001. Significantly more patients were found to have abnormal bone according to TBS (72.3%) compared to DXA (47.6%), p < 0.001. Whereas TBS and DXA T-scores were moderately correlated, r = 0.50, p < 0.001; TBS T-scores (M = -1.97, SD = 1.31) were significantly lower than DXA T-scores (M = -0.79, SD = 1.56), t(190) = 11.17, p < 0.001. There were 153 cases (80.1%) for which the TBS T-score was less than the corresponding DXA T-score. There was no statistically significant difference in mean DXA T-scores between male (M = -0.67, SD = 1.50) and female patients (M = -0.99, SD = 1.65), t(189) = 1.40, p = 0.16. However, women (M = -2.40, SD = 1.50) had significantly lower mean TBS T-scores than men (M = -1.71, SD = 1.10), t(189) = 3.58, p < 0.001. Hispanic patients (M = -1.13, SD = 1.56) had significantly lower BMD compared to white (M = -0.40, SD = 1.13) or black patients (M = -0.12, SD = 1.68), F(4, 155) = 5.67, p < 0.001. In contrast, microarchitecture did not differ by race/ethnicity, F(4, 155) = 0.35, p = 0.84.

Conclusion:
Like osteoporosis, impaired trabecular microarchitecture is extremely common among lung transplant candidates. A substantial proportion of patients remain at risk of fracture through degraded bone despite normal BMD. TBS offers promise as a simple, inexpensive, noninvasive, and readily available adjunct to DXA in this unique and vulnerable population. Interestingly, TBS may be robust against racial/ethnic disparities traditionally encountered in BMD screening.