Magnetic resonance spectroscopy (MRS) may accurately identify painful lumbar disks in patients with chronic low back pain (CLBP) and was found to strongly correlate with provocation discography (PD) identification, according to a study published in the European Spine Journal.

Although PD is considered the standard diagnostic tool for diskogenic CLBP, it is an expensive, invasive, and risky procedure. Biomarkers identified with MRS may represent an attractive alternative. Investigators sought to evaluate MRS for its ability to accurately and reliably identify painful discs and assess their degeneration, as well as predict surgical outcomes.

In this multicenter observational study, a total of 139 patients with CLBP were enrolled (mean age, 41; 32% women; mean Oswestry Disability Index [ODI], 56.5). A total of 623 disks were assessed with single-voxel MRS scannin, and 275 disks were evaluated with PD. Data from MRS scans were used to quantify disc structural integrity (via analysis of collagen and proteoglycan) and acidity (via analysis of lactate, alanine, and propionate). 

Acidity is thought to constitute a biomarker for pain, as it increases with pain-associated phenomena (eg, inflammation, hypoxia). Acidity to structural integrity ratios (6 in total) were calculated to evaluate the “pain potential,” weighted and summed, resulting in total MRS-SCOREs, which were then normalized (normalized MRS-SCOREs on a 0-1 scale). Normalized MRS-SCOREs were compared with Pfirrmann grades and PD results and rated positive (MRS+) or negative (MRS−). There were 84 participants who underwent lumbar spinal surgery at painful sites, with 73 and 62 individuals reaching 6- and 12-month follow-up assessments, respectively.

Disks were categorized as painful or non-painful, as well as PD+ or PD−, in addition to MRS+ or MRS−. The primary outcome was the correlation between MRS results, pain, and PD status. Secondary outcomes included a 15-point improvement on the ODI, and a 2-point improvement on a 1 to 10 visual analog scale (VAS) after surgery.

A total of 206 disks received an independent pain diagnosis and a successful MRS. There were significant differences in MRS-SCOREs between painful and non-panful discs (P <2.10-16) and between PD+ and PD− discs (P <2.10-15). MRS had an estimated accuracy of 85% compared with PD with a sensitivity of 82% and a specificity of 88%. When only non-herniated discs were analyzed, MRS accuracy improved to 93%, with 91% sensitivity and 93% specificity. Measurements of structural integrity using MRS were significantly different from Pfirrmann grades, with the exception of grade I vs grade II.

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Participants who had all MRS+ disks repaired had a 97% success rate after surgery. In contrast, the success rate was 57% when MRS− discs were corrected, and 54% in patients with MRS+ adjacent non-treated discs. At 6- and 12-months follow-up, surgical success was >90% vs approximately 50% when treated discs were MRS+ and MRS− disks, respectively. Patients who underwent surgery on MRS+ vs MRS− disks improvements in ODI scores (P <.005 and P <.05, respectively) and VAS scores (P <.05 for both) reported at 6 and 12 months.

Study limitations include a short follow-up period.

“MRS correlates with PD and may support improved surgical outcomes for [patients with] CLBP. Noninvasive MRS is a potentially valuable approach to clarifying pain mechanisms and designing CLBP therapies that are customized to the patient,” noted the authors.

Disclosure

Some authors have a financial relationship with the sponsor of the study (MGG, JP, JC, FWS, RKE, and JCL). The authors have full control of all primary data and agree to allow the journal to review data if requested.

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Reference

Gornet MG, Peacock J, Claude J, et al. Magnetic resonance spectroscopy (MRS) can identify painful lumbar discs and may facilitate improved clinical outcomes of lumbar surgeries for discogenic pain [published online January 4, 2019]. Eur Spine J. doi:10.1007/s00586-018-05873-3