Evaluation of Bone Mineral Density Using DXA and cQCT in Postmenopausal Patients Under Thyrotropin Suppressive Therapy

This study aimed to examine the discrepancy in osteoporosis diagnoses between central quantitative computed tomography (cQCT) and dual-energy X-ray absorptiometry (DXA) and evaluated correlations among volumetric bone mineral density (vBMD), areal bone mineral density (aBMD), and trabecular bone score(TBS) in postmenopausal women who were undergoing TSH suppressive therapy. We enrolled a total of 81 postmenopausal patients [median age: 58 years; interquartile range (IQR): 57 to 60 years] receiving TSH suppressive therapy with levothyroxine after undergoing total thyroidectomy for papillary thyroid cancer. Patients were diagnosed by their bone mineral density (BMD) T-score and categorized according to a vBMD threshold of 120 mg/cm3 for osteopenia and a threshold of 80 mg/cm3 for osteoporosis. When DXA and cQCT were compared, the BMD evaluation results differed in 76% of patients (n = 62; P < 0.001), and the detection rate of osteoporosis was 30.9% for cQCT and 21.0% for DXA. Sixty-two patients had discordant results; in 46 of these patients (74%) whose DXA T-scores were normal, the diagnosis shifted to osteopenia (n = 35) and osteoporosis (n = 11) according to the vBMD on cQCT (P < 0.001), and their vBMD values were significantly correlated with TBS (r = 0.293; P = 0.008). However, aBMD was not significantly correlated with TBS (r = 0.080; P = 0.480). TBS was significantly lower in patients with osteopenia (median: 1.35; IQR: 1.18 to 1.47) and osteoporosis (median: 1.28; IQR: 1.07 to 1.47) than in those with a normal BMD value (median: 1.37; IQR: 1.25 to 1.49; P = 0.041) on cQCT. There was no significant difference in TBS according to DXA BMD status (P = 0.200). DXA and cQCT yielded inconsistent results, and detection of osteopenia and osteoporosis was higher using cQCT. TBS showed a more significant correlation with vBMD than with aBMD.