GAG content

Goal of the Study?

In this study 1, the authors’ goal was to assess the GAG contents of lumbar IVDs in disorders of the spine, including non-specific lower back pain (nsLBP) and radiculopathy, against asymptomatic volunteers to determine the potential influence of IVD protrusions on the GAG contents of adjacent IVDs.

 

Why are they doing this study?

Low back pain (LBP) is a common health burden that has significant implications for individuals and society. Most LBP is non-specific (nsLBP) and without a known cause. One potential factor contributing to nsLBP is lumbar degenerative disk disease (LDDD). A common structural disorder that leads to LBP is lumbar IVD extrusion with radiculopathy. While MRI for diagnosis of LBP is controversial, it is the most commonly used technique for looking at the morphological changes in LDDD, such as IVD dehydration and loss of IVD height. However, to detect early structural changes to cartilage, the use of the non-invasive compositional MRI technique GAG Chemical Exchange Saturation Transfer (gagCEST) is preferred. Existing research has demonstrated how gagCEST images can help to differentiate degenerative and non-degenerative IVDs based on their respective GAG contents. To that end, the authors hypothesized that the GAG contents in patients with nsLBP and radiculopathy are significantly lower than in asymptomatic volunteers and that the GAG content of lumbar IVDs adjacent to extruded IVDs is markedly lower than that of non-adjacent IVDs.

 

What was done?

In total, they recruited 18 patients with radiculopathy and IVD extrusion, 16 age-matched patients with chronic nsLBP and 20 age-matched volunteers. All of these participants underwent morphologic and compositional gagCEST MRI. Patients were assessed by an orthopedic surgeon and underwent a neurologic exam, with a focus on radicular pain, distal sensation and muscle strength. All participants’ lumbar IVDs were graded individually and independently using the Pfirrmann classification (non-degeneration) grades 1 and 2; degenerative IVDs (grades 3-5). Statistical software was used to determine statistical significance.

 

What did they find?

Patients with radiculopathy demonstrated IVD extrusions at the IVD segments L4/5 and L5/S1, compared to patients with nsLBP or asymptomatic volunteers who showed none. No differences in Pfirrmann grades were found between patients with nsLBP and patients with radiculopathy and patients with radiculopathy and asymptomatic volunteers. Regarding gagCEST values, the authors found that patients with nsLBP demonstrated lower gagCEST values in their IVDs than those of volunteers, with 1.3% and 1.9%, respectively. However, there were no differences in gagCEST values between patients with radiculopathy and asymptomatic volunteers or female and male participants. Finally, in patients with radiculopathy, IVDs directly adjacent to IVD extrusions showed lower gagCEST values than distant IVDs. The authors argue that GAG depletion in nsLBP and IVDs adjacent to extrusions in radiculopathy demonstrates close interrelatedness between clinical pathology and the compositional and structural changes to IVDs in the degeneration of the lumbar spine. 

 

Why do these findings matter?

Non-invasive gagCEST imaging provides potential diagnostic value to detect early changes to tissue composition and pre-morphological IVD degeneration. It serves to differentiate patterns of IVD degeneration in disorders of the lumbar spine. Early detection can lead to better diagnosis, care and treatment of lumbar spine disorders in patients.

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