By Markus Melloh and Thomas Barz
The US Centers for Medicare & Medicaid Services, in a 2013 review of lumbar spinal stenosis, state there is no consensus and only insufficient evidence for the definition of lumbar spinal stenosis or the accuracy of diagnostic tests, including which clinical signs and symptoms originate from lumbar spinal stenosis1. However, there is growing evidence that the “nerve root sedimentation sign” (SedSign) could aid the diagnosis of the condition. Markus Melloh and Thomas Barz, who invented the SedSign, review the evidence base for this prospective diagnostic tool
Despite a justified critique by Haig2 of MRI, in which he wrote that “simply ordering an MRI is no more useful than ordering a pizza” and “the most sensitive test for lumbar stenosis may be the presence of an opposable thumb”, the imaging modality is still indicated for the diagnosis and differential diagnosis of patients with neurogenic claudication. In 2010, Barz and Melloh et al published their observations of a phenomenon seen on MRI scans in the supine position of patients with lumbar spinal stenosis3—they found that nerve roots did not follow gravity but remained in the ventral and central part of the dural sac. In contrast, patients without lumbar spinal stenosis showed lumbar nerve root sedimentation to the dorsal part of the dural sac. The authors named this phenomenon the “nerve root sedimentation sign” (SedSign) and defined absence of sedimented nerve roots as a positive sign.
The evidence base for the SedSign
Since its introduction, a further six studies on the SedSign have been published4–9. Another study, on data from the Spine Patient Outcomes Research Trial (SPORT), is currently under review. Apart from the inventors’ proof-of-concept study9, all related studies have been retrospective—with one study comparing four groups (lumbar spinal stenosis/low back pain/vascular claudication/asymptomatic controls) and another study comparing three groups but most compared two groups.
In these studies (aside from the proof-of-concept study), sample sizes have varied from 71 to 444 patients and three studies (including SPORT) have provided follow-up data. All studies investigated the potential diagnostic value of the SedSign, with four of them focusing on its potential as an aid for indicating surgery.
Six of the studies have reported SedSign sensitivity as approximately 90% but specificity has generally not been reported. Four studies stated an interobserver reliability of around 90%, but intraobserver reliability was only reported by two studies (with one study3 showing an intraobserver reliability of 1.0). Also, the studies showed that a positive SedSign was associated with multilevel lumbar spinal stenosis and a three-fold higher epidural pressure at the stenosis level compared with patients without lumbar spinal stenosis and a negative SedSign. According to unpublished data from SPORT, in patients with a positive SedSign surgical treatment was associated with significant larger improvements in function compared with non-surgical treatment.
The use of the SedSign in determining the management of patients with lumbar spinal stenosis
Evidence from these eight studies (the seven published studies and the ongoing SPORT study) suggests that the SedSign could be useful as an add-on tool for surgical decision-making in lumbar spinal stenosis. The inventors of the SedSign believe it is a simple, reliable, and cost-effective indicator of lumbar spinal stenosis with significant advantages compared to solely assessing the cross-sectional area of the dural sac10,11. Furthermore, use of the SedSign is fast, does not require taking additional measurements, and demonstrates the stenosis in a way that can easily be explained to the patient. It additionally provides supplementary information to other diagnostic tests and could help in identifying patients who may benefit from decompression surgery. However, further research is required—incorporating both testing and treatment—to determine how specifically the SedSign predicts treatment outcomes and identifies which segmental levels to include in decompression surgery12,13.
Looking to the future, patients might benefit from an additional tool recently described by Barz Melloh et al and further developed with co-inventor Raoul Hecker. Epidural pressure measurement at stenosis level might improve the diagnostic accuracy in lumbar spinal stenosis compared with using MRI and clinical examination alone. This technique could be used before or during surgery helping to identify which segments require decompression.
1. Centers for Medicare & Medicaid Services, Proposed Decision Memo for Percutaneous Image-guided Lumbar Decompression for Lumbar Spinal Stenosis (CAG-00433N). Accessed 14 Feb 2014; www.cms.gov/medicare-coveragedatabase/details/nca-proposed-decisionmemo.aspx?NCAId=269
2. Haig. Spine J 2014; 14: 200–01
3. Barz and Melloh et al Spine. 2010; 35: 892¬–97
4. Kim et al. J Korean Soc Spine Surg 2011; 18:117–22
5. Macedo et al. Spine 2013; 38: 827–31
6. Fazal et al. Spine J 2013; 13: 837–42
7. Tomkins-Lane et al. Spine 2013; 38: E1554–60
8. Barz and Staub et al. Spine J; Epub 2013 Sept 19
9. Barz and Melloh et al. Eur Spine J.; Epub 2013 Oct 29
10. Barz et al. Spine 2013; 35: E1360
11. Khanna. Spine J 2013; 13: 843–4
12. Herzog. Spine 2013; 38: 832
13. Melloh et al. Spine J; accepted for publication
Markus Melloh is the inaugural director of the new Centre for Health Sciences, School of Health Professions, Zurich University of Applied Sciences, Winterthur, Switzerland and Thomas Barz is at Asklepios Klinikum Uckermark, Schwedt, Germany