Synopsis

In this study, we address the lack of studies comparing intervertebral disc characteristics between symptomatic and asymptomatic individuals. Based on quantitative T2-mapping, small but relevant differences between low back pain patients and a control cohort were found on a global and regional level.

Introduction

Intervertebral disc (IVD) degeneration can be evaluated by conventional ¹ and functional MRI ². Both can provide objective continuous IVD-degeneration measures when evaluated with quantitative morphometric ^3,4 and innovative histogram analysis ⁵. However, the exact relation between IVD-degeneration and low back pain (LBP) is not fully elucidated and there are limited studies comparing detailed quantitative IVD characteristics of symptomatic and asymptomatic individuals.

As the IVD tissue display regional variation in T2-relaxation time and both biomechanical load and degeneration often are unevenly distributed ⁶, it is desirable to investigate the IVD on a more detailed regional scale.

The aim was to analyse T2-maps in detail to find differences in IVD tissue characteristics between LBP-patients and asymptomatic individuals.

Materials and Methods

Twenty-five LBP-patients (124 IVDs, 20 of which have HIZ, 11 males, mean 38y, range 25-69y) and 12 matched controls (59 IVDs, 4 of which have HIZ, 7 males, mean 38y, range 25-59y) were examined with T2-mapping on a 1.5T MRI scanner (Siemens Magnetom Aera, Erlangen, Germany). All IVDs were graded twice with the Pfirrmann score ⁷ by an experienced radiologist.

For all IVDs, the mean T2-values and standard deviations (SD) were analysed globally and regionally (Figure 1). Histogram analysis, proposed by Waldenberg et al.⁵, was also performed to provide additional quantitative metric (Δµ) describing the IVD tissue structure.

Statistical significance between groups was determined with Mann-Whitney U-test at P<0.05, except for Pfirrmann grade 5 due to too small sample size.

Results

For both patients and controls, the global IVD T2-relaxation time, SD and Δµ all decreased with increased degeneration (Figure 2). For all these investigated metrics, significant difference between patients and controls was found for IVDs with Pfirrmann grade 4. After re-scoring of Pfirrmann (κ = 0.74), significance for all metrics was also found for Pfirrmann grade 3.

Compared to controls, patient IVDs generally reached lower median and mean values for all metrics, with significant differences for SD and Δµ.

Regional analysis revealed significant differences between patients and controls in regions with the highest T2-relaxation time, i.e. subregion 3 and 4 (Figure 3).

Discussion

This study, analysing quantitative IVD characteristics, found on a global and regional level small but relevant quantitative IVD differences between patient and control cohorts.

Significant differences between patients and controls were found for IVDs with Pfirrmann grade 4 that might reflect tissue characteristics related to LBP. However, the Pfirrmann grading is based on visual interpretation and as such the result may reflect interpreter sensitivity. Nonetheless, comparing all patient’s IVDs to all control’s IVDs, regardless of Pfirrmann grade, significant differences in sub-regions occupied by nucleus pulposus (NP) (3 and 4) were found. The lower T2-values found in these regions might reflect disturbed nutrient transport ⁸, which in turn might alter the tissue composition of the NP ⁹. Such effect could be directly related to LBP but could also be a consequence of LBP, e.g. LBP-patients may have a reduced physical activity and, hence, reduced nutrition transport ¹⁰. Large-scale interventional studies should be conducted to strengthen the conclusion.

Besides exploring differences between patients and controls, this study shows, on a group and individual level, that the regional T2-value variation is a promising marker for disc status. The variation in T2-value over the IVD follows a general pattern with low T2-values at the anterior and posterior sub-regions and the highest T2-value located slightly off-center towards the posterior side. Changes in this behaviour may reveal individual patterns of significance.

Conclusion

Acknowledgements

References

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