No relationship between bone mineral density and syndesmophyte formation at the same level in the lumbar spine of patients with radiographic axial Spondyloarthritis

The state of bone mineral density in men with ankylosing spondylitis and its relationship with the course of the disease

Introduction

The aim of the study was to study the structural and functional state of bone tissue in men with ankylosing spondylitis (AS) and to assess its relationship with the course of the disease.

Material and methods

A study was conducted with the participation of 105 men with AS aged from 22 to 59 years (average age was 40.7 ±0.8 years) with a duration of the disease of 8.7 ±0.5 years and 29 persons of the control group. Disease activity and the degree of functional limitations were determined by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Ankylosing Spondylitis Activity Score correlated with C-reactive protein (ASDAS-CRP) and the Bath Ankylosing Spondylitis Functional Index (BASFI). Laboratory examination included determination of C-reactive protein (CRP). Bone mineral density (BMD) of the lumbar spine and femoral neck was determined by the method of dual-energy X-ray absorptiometry on the Hologic Discovery Wi device (S/N 87227).

Results

In men with AS, a decrease in BMD (according to the Z-score and T-score) was found in 41.9%, while the percentage of patients with osteoporosis at the level of the femoral neck and lower back was 16.7%. Development of osteoproliferative changes was observed in 42 (40%) patients. Bone mass loss was associated with high activity of the inflammatory process according to ASDAS, BASDAI (r = -0.39, -0.65), and CRP (r = -0.28, -0.38) and low functional capacity according to BASFI (r = -0.27, -0.59), while syndesmophytosis had a reliable association with the age of the patients, the duration of the disease and low functional capacity. Low-energy fractures occurred in 11.4% of men with AS. The presence of fractures was associated with high disease activity (ASDAS, BASDAI, CRP) and was not related to the age of the patients or duration of the disease.

Conclusions

A decrease in BMD and the development of fractures were closely associated with high activity of the inflammatory process and low functional capacity, while syndesmophytosis was related to the age of patients and the duration of the disease.

Syndesmophyte Growth in Ankylosing Spondylitis: from Laboratory to Bedside

PURPOSE OF REVIEW

This study aims to review recent studies on risk factors for syndesmophyte growth in ankylosing spondylitis (AS) and on treatment effects.

RECENT FINDINGS

New genetic studies, including a genome-wide association study, provided only limited evidence of specific genetic associations with radiographic severity. Measures of inflammation, including vertebral osteitis and C-reactive protein level, were strongly associated with radiographic progression, while studies of adipokines had mixed results. Mesenchymal stem cells from HLA-B27 positive AS patients were found to promote vertebral ossification via a pathway of B27 misfolding, retinoic acid receptor-β activation, and increased bone alkaline phosphatase. Low vertebral trabecular bone density is associated with syndesmophyte growth, with reciprocal effects when bridged. Several observational studies suggested radiographic severity was reduced by treatment with tumor necrosis factor inhibitors, particularly when longer than 2 years. Syndesmophyte development in AS is the result of a complex, incompletely understood, interplay of inflammatory and mechanical factors.

Inflammation, bone loss and 2-year bone formation at the same vertebra in axial spondyloarthritis: a multilevel MRI and low-dose CT analysis

OBJECTIVE

To investigate whether in radiographic axial spondyloarthritis (r-axSpA) inflammation is associated with lower trabecular bone density (TBD), and subsequently, if a lower TBD increases the likelihood of 2-year bone formation at the same vertebra.

METHODS

Whole spine (C3-L5) data from patients included in the multicentre 2-year Sensitive Imaging in Ankylosing Spondylitis cohort was used. Two readers measured baseline TBD by Hounsfield units (HU) on low-dose CT (ldCT). Baseline MRI bone marrow oedema (BME) status scores and ldCT syndesmophyte formation and/or growth change-from-baseline scores were assessed by three and two readers, respectively. Average of readers' continuous measurements or readers' agreement in binary scores generated within the same vertebra (1-present in ≥1 quadrant/0-absent in all quadrants) were used. Multilevel generalised estimating equations models were used, the unit of analysis being the vertebra.

RESULTS

In 50 patients with r-axSpA, TBD HU decreased from cranial to caudal vertebrae. Baseline MRI-BME was present in 300/985 (30%) and syndesmophytes in 588/910 (65%) vertebrae, both most prevalent at thoracolumbar region. Syndesmophyte formation or growth was observed in 18% of at-risk vertebrae (124/691). A significant confounder-adjusted association was found between inflammation and lower TBD (regression coefficient=-51; 95% CI-63 to -39). TBD was not associated with 2-year syndesmophyte formation or growth (adjusted OR 1.00; 95% CI 0.99 to 1.00).

CONCLUSION

In r-axSpA, while vertebral inflammation was associated with lower vertebral TBD, lower vertebral TBD itself did not increase the risk for new bone formation at the same vertebra. In preventing syndesmophyte progression, targeting local inflammation seems more important than targeting vertebral trabecular bone loss.

Hounsfield Units measured in low dose CT reliably assess vertebral trabecular bone density changes over two years in axial spondyloarthritis

OBJECTIVES

To describe low dose Computed Tomography (ldCT) Hounsfield Units (HU) two-year change-from-baseline values (expressing trabecular bone density changes) and analyse their inter-reader reliability per vertebra in radiographic axial spondyloarthritis (r-axSpA).

METHODS

We used 49 patients with r-axSpA from the multicentre two-year Sensitive Imaging in Ankylosing Spondylitis (SIAS) study. LdCT HU were independently measured by two trained readers at baseline and two years. Mean (standard deviation, SD) for the change-from-baseline HU values were provided per vertebra by reader. Intraclass correlation coefficients (ICC; absolute agreement, two-way random effect), Bland-Altman plots and smallest detectable change (SDC) were obtained. Percentages of vertebrae in which readers agreed on the direction of change and on change >|SDC| were computed.

RESULTS

Overall, 1,053 (98% of all possible) vertebrae were assessed by each reader both at baseline and two years. Over two years, HU mean change values varied from -23 to 28 and 29 for reader 1 and 2, respectively. Inter-reader reliability of the two-year change-from-baseline values per vertebra was excellent: ICC:0.91-0.99; SDC:6-10; Bland-Altman plots were homoscedastic, with negligible systematic error between readers. Readers agreed on the direction of change in 88-96% and on change >|SDC| in 58-94% of vertebrae, per vertebral level, from C3 to L5. Overall, similar results were obtained across all vertebrae.

CONCLUSION

LdCT measurement of HU is a reliable method to assess two-year changes in trabecular bone density at each vertebra from C3-L5. Being reliable across all vertebrae, this methodology can aid the study of trabecular bone density changes over time in r-axSpA, a disease affecting the whole spine.

Vertebral Bone Mineral Density, Vertebral Strength, and Syndesmophyte Growth in Ankylosing Spondylitis: The Importance of Bridging

OBJECTIVE

To examine the relationship between vertebral trabecular bone mineral density (tBMD), vertebral strength, and syndesmophytes in patients with ankylosing spondylitis (AS) using quantitative computed tomography (QCT).

METHODS

We performed QCT of the spine to measure syndesmophytes and tBMD in 5 vertebrae (T11-L3) in 61 patients with AS. Finite element analysis was performed to measure vertebral strength in compressive overload, including in trabecular and cortical compartments. In cross-sectional analyses, we examined associations of syndesmophyte height with tBMD and vertebral strength in each vertebra. In 33 patients followed up for 2 years, we investigated whether baseline tBMD and vertebral strength predicted syndesmophyte growth in the same vertebra, and vice versa.

RESULTS

In the cross-sectional analyses, 126 vertebrae had bridging, 77 vertebrae had nonbridging syndesmophytes, and 83 vertebrae had no syndesmophytes. There were strong inverse associations between syndesmophyte height and tBMD, total strength, and trabecular strength only among bridged vertebrae. In the longitudinal analysis, nonbridged vertebrae with low tBMD (adjusted β = -0.01 [95% confidence interval (95% CI) -0.019, -0.0012]) and low strength (adjusted β = -0.0003 [95% CI -0.0004, -0.0002]) had more syndesmophyte growth over time. Similar associations were absent among bridged vertebrae. Conversely, vertebrae with bridging at baseline had a significant loss in percent tBMD over time (adjusted β = -0.001 [95% CI -0.0017, -0.0004]).

CONCLUSION

Associations between syndesmophytes and vertebral density and strength in AS differ between bridged and nonbridged vertebrae. Among nonbridged vertebrae, low tBMD and strength are associated with syndesmophyte growth. Bridging is associated with large subsequent losses in tBMD, possibly due to mechanical offloading.

Low-dose CT hounsfield units: a reliable methodology for assessing vertebral bone density in radiographic axial spondyloarthritis

Objective

Studying vertebral bone loss in radiographic axial spondyloarthritis (r-axSpA) has been challenging due to ectopic bone formation. We cross-sectionally analysed low-dose CT (ldCT) trabecular bone density Hounsfield units (HU) measurements and calculated inter-reader reliability at the vertebral level in patients with r-axSpA.

Methods

LdCT scans of 50 patients with r-axSpA from the sensitive imaging in ankylosing spondylitis study, a multicentre 2-year prospective cohort were included. Trabecular bone HU taken from a region of interest at the centre of each vertebra (C3-L5) were independently assessed by two trained readers. HU mean (SD), and range were provided at the vertebral level, for each reader and centre separately. Inter-reader reliability and agreement were assessed using intraclass correlation coefficients (ICC; single measurements, absolute agreement, two-way mixed effects models); smallest detectable difference and Bland-Altman plots.

Results

Overall, 1100 vertebrae were assessed by each reader. HU values decreased from cranial to caudal vertebrae. For readers 1 and 2 respectively, the highest mean (SD) HU value was obtained at C3 (354(106) and 355(108)), and the lowest at L3 (153(65) and 150 (65)). Inter-reader reliability was excellent (ICC(2,1):0.89 to 1.00). SDD varied from 4 to 8. For most vertebrae, reader 1 scored somewhat higher than reader 2 (mean difference of scores ranging from −0.6 to 2.9 HU). Bland-Altman plots showed homoscedasticity.

Conclusion

LdCT measurement of HU is a feasible method to assess vertebral bone density in r-axSpA with excellent inter-reader reliability from C3 to L5. These results warrant further validation and longitudinal assessment of reliability.