The Value of Trabecular Bone Score in the Evaluation of Bone Quality in a Patient with Ankylosing Spondylitis

Abstract

Patients with ankylosing spondylitis (AS) have an increased risk of developing osteoporosis, mainly caused by systemic inflammation and decreased mobility (1). For this reason, patients with AS demonstrate an increased risk of fractures, especially vertebral fractures, in comparison with the general population (2). However, measurements of areal bone mineral density (aBMD) are overestimated and unreliable in AS patients, because of the presence of osteo-proliferation and syndesmophytes. Significantly increased aBMD measures have been reported in patients with advanced AS (3). Consequently, the diagnosis of osteoporosis could be difficult in affected patients (1).Considering bone microarchitecture as another determinant of bone strength, and regarding less impact of osteoproliferation on bone microarchitecture, it could be a better predictor of bone strength in these patients (4). Trabecular bone score (TBS), a new noninvasive tool for the measurement of bone microarchitecture, could be used complementary to aBMD in the evaluation of bone quality in AS patients (5). In this letter, the authors discuss the value of TBS in the evaluation of bone quality in a patient with AS, and discuss its advantages over aBMD.A 47-year-old male with a 10-year history of inflammatory back pain was referred to the researcher's center. Acute phase reactants including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were elevated and positive HLA-B27 was found. Other laboratory tests were within the normal range. Typical syndesmophytes were also observed in the spinal X-rays of the patient. The diagnosis of AS was made according to the assessment of spondylo arthritis international society (ASAS) criteria. Subsequently, the therapeutic approach was started with an anti-inflammatory dose of indomethacin. However, considering the patient's unresponsiveness, infliximab was added to his therapeutic regimen.Given the 10-year history of the disease, osteoporosis evaluation was indicated for the patient and aBMD was ordered. Considering the normal aBMD results of the patient (T-score > -1), according to the world health organization (WHO) criteria, no osteoporosis treatment was indicated for the patient. However, since the aBMD results was probably artifactually elevated by the presence of typical syndesmophytes, the patients was asked to recheck the aBMD results in another center, which was equipped to the TBS software. While the aBMD results of the second exam were the same as the first one, the patient's bone microarchitecture was classified as fully degraded (TBS ≤ 1.20). Consequently, zoledronic acid (Aclasta) was administered as the osteoporosis therapeutic agent.The case showed that regarding the presence of sindesmophytes, aBMD is not a reliable marker for the evaluation of bone quality in the affected patients (1). Considering the presence of typical syndesmophytes in the X-rays of the patient's vertebrae, the authors concluded that the aBMD is probably overestimated, and TBS could be more helpful in the evaluation...

Review of the Clinical Applications of Trabecular Bone Score

“…Other studies have also report that TBS accurately diagnosed axial osteoporosis in the early stages of AS, while BMD is not a reliable tool. Moreover, TBS is reported to be capable of predicting spine fractures independent of FRAX in AS patients [45][46][47].…”