Lumbar spinal stenosis diagnosis
Diagnosing lumbar spinal stenosis or herniated intervertebral disc is usually helpful only in potential surgical candidates 1).
Boden et al., performed magnetic resonance imaging on sixty-seven individuals who had never had low back pain, sciatica, or neurogenic claudication. The scans were interpreted independently by three neuro-radiologists who had no knowledge about the presence or absence of clinical symptoms in the subjects. About one-third of the subjects were found to have a substantial abnormality. Of those who were less than sixty years old, 20 per cent had a herniated nucleus pulposus and one had spinal stenosis. In the group that was sixty years old or older, the findings were abnormal on about 57 per cent of the scans: 36 per cent of the subjects had a herniated nucleus pulposus and 21 per cent had spinal stenosis. There was degeneration or bulging of a disc at at least one lumbar level in 35 per cent of the subjects between twenty and thirty-nine years old and in all but one of the sixty to eighty-year-old subjects. In view of these findings in asymptomatic subjects, they concluded that abnormalities on magnetic resonance images must be strictly correlated with age and any clinical signs and symptoms before operative treatment is contemplated 2).
Results of a survey suggested that there are no broadly accepted quantitative criteria and only partially accepted qualitative criteria for the diagnosis of lumbar spinal stenosis. The latter include disk protrusion, lack of perineural intraforaminal fat, hypertrophic facet joint degeneration, absent fluid around the cauda equine, and hypertrophy of the ligamentum flavum 3).
There is still no widely accepted diagnostic or classification criteria for the diagnosis of Lumbar spinal canal stenosis LSS and as a consequence studies use widely differing eligibility criteria that limit the generalizability of reported findings 4).
There are no universally accepted radiographic definitions for the diagnosis of central, lateral recess and foraminal stenosis.
Most studies of Lumbar central canal spinal stenosis diagnosis (LCCSS) rely on criteria published by Verbiest et al. 5). He defined relative spinal stenosis as a diameter between 10 and 12 mm whereas absolute stenosis was a diameter less than 10 mm. This method has been criticized for ignoring the trefoil shape of the LSS and the intrusion of ligamentum flavum and disc material in degenerative stenosis 6).
Magnetic resonance imaging
Magnetic resonance imaging (MRI) is most commonly used for the clinical assessment of degenerative LCCSS. LCCSS is a quantitative diagnosis that is made when the measurement of an individual is outside the range of normal. Thus, the criteria for LCCSS should be compared from an analysis of a normative distribution of measurements 7) 8)
In a meta-analysis, CT and MRI were found to have similar accuracy for the assessment of central stenosis 9).
By using a combination of magnetic resonance imaging (MRI) and computed tomography (CT) of the lumbar spine, it is possible to distinguish between spinal stenosis caused by bone compression and specific soft tissue epidural intraspinal lesions that cause localized spinal canal stenosis and neural compression. Examples include facet cysts and yellow ligament hypertrophy 10).
Because imaging findings of lumbar spinal stenosis (LSS) may not be associated with symptoms, clinical classification criteria based on patient symptoms and physical examination findings are needed 11).
Magnetic resonance imaging (MRI) has replaced myelography, now considered an old-fashioned technique. In selected cases with multilevel lumbar spinal stenosis, functional myelography revealed the highest precision in reaching a correct diagnosis. It resulted in a change in the surgical approach in every fifth patient in comparison with the MRI and proved most helpful, especially in elderly patients 12).
Cross sectional area
Narrowing of the lumbar dural sac cross sectional area (DSCSA) and spinal canal cross-sectional area (SCCSA) have been considered major causes of lumbar central canal spinal stenosis (LCCSS). DSCSA and SCCSA were previously correlated with subjective walking distance before claudication occurs, aging, and disc degeneration. DSCSA and SCCSA have been ideal morphological parameters for evaluating LCCSS.
To evaluate lumbar central canal spinal stenosis (LCCSS) patients, pain specialists should more carefully investigate the dural sac cross-sectional area (DSCSA) than spinal canal cross-sectional area (SCCSA) 13).
Schonstrom et al. showed that neurogenic claudication due to LSS was better defined by the cross-sectional area (CSA) of the dural sac, but that the CSA of the lumbar vertebral canal was unrelated to that of the dural sac 14). From in vitro 15) and in situ 16) studies, the authors postulated that constrictions above the critical size 70 to 80 mm2 would be unlikely to cause symptoms and signs of cauda encroachment. Subsequently, conflicting results have been published concerning the relationship between symptom severity and dural CSA. Even after axial loading, no statistically significant correlations were found in some studies 17). However, in another study, the use of the minimal CSA of the dural sac in central stenosis was found to be correlated with neurogenic claudication assessed measuring the maximum tolerated walking distance 18).
Patients with symptoms, physical examination and imaging findings consistent with LSS do not require additional testing. Although there is little evidence in the literature, electrodiagnostic evaluation is used in some patients with symptoms and findings that are equivocal or conflicting with imaging results and in whom procedures are being considered. Electrodiagnostic criteria for stenosis have been proposed:(47) mini-paraspinal mapping with a one side score > 4 (sensitivity 30%, specificity 100%), fibrillation potential in limb muscles (sensibility 33%, specificity 88%), absence of tibial H-wave (sensitivity 36%, specificity 92%). Better sensitivity was found for a composite limb and paraspinal fibrillation score (sensitivity 48%, specificity 88%) 19).
Jensen et al. developed a self-administered diagnostic screening questionnaire for lumbar spinal stenosis (LSS) consisting of items with high content validity and to investigate the diagnostic value of the questionnaire and the items.
The screening questionnaire was developed based on items from the existing literature describing key symptoms of LSS. The screening questionnaire (index test) was to be tested in a cohort of patients with persistent lumbar and/or leg pain recruited from a Danish publicly funded outpatient secondary care spine clinic with clinicians performing the reference test. However, to avoid unnecessary collection of data if the screening questionnaire proved to be of limited value, a case-control design was incorporated into the cohort design including an interim analysis. Additional cases for the case-control study were recruited at two Danish publicly funded spine surgery departments. Prevalence, sensitivity, specificity and diagnostic odds ratio (OR) were calculated for each individual item, and AUC (area under the curve) was calculated to examine the performance of the full questionnaire.
A 13-item Danish questionnaire was developed and tested in 153 cases and 230 controls. The interim analysis was not in favour of continuing the cohort study, and therefore, only results from the case-control study are reported. There was a positive association for all items except the presence of back pain. However, the association was only moderate with ORs up to 3.3. When testing the performance of the whole questionnaire, an AUC of 0.72 was reached with a specificity of 20% for a fixed sensitivity of 95%.
The items were associated with LSS and therefore have some potential to identify LSS patients. However, the association was not strong enough to provide sufficient accuracy for a diagnostic tool. Additional dimensions of symptoms of LSS need identification to obtain a reliable questionnaire for screening purposes 20).