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Year : 2013  |  Volume : 40  |  Issue : 1  |  Page : 27-32

Spinal N22 in diagnosing lumbosacral radiculopathy

Physical Medicine, Rheumatology and Rehabilitation Department, Faculty of Medicine, Alexandria University, Alexandria, Egypt

Correspondence Address:
Mohamed Hassan Imam
574 Horreya Avenue Gleem, Appartement 5, 02030 Alexandria
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Source of Support: None, Conflict of Interest: None

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Introduction The spinal (N22) wave is generated postsynaptically in the gray matter of the lumbar cord. Short-latency somatosensory-evoked responses to tibial nerve stimulation were recorded simultaneously over the spinous processes of the lumbar vertebrae and scalp. This noninvasive test yielded values that are highly reproducible and could be correlated closely with patient-related variables such as height and leg length. Most studies on somatosensory-evoked potentials (SEPs) in cases of lumbosacral radiculopathy routinely analyze scalp (cortical) responses, depending mainly on the evaluation of P40 and the dermatomal somatosensory-evoked potential (DSEP) whose origin is the primary somatosensory cortex. It was suggested that a selective study of the N22 potential might be a useful technique to improve both the accuracy and the sensitivity of the diagnosis of lumbosacral radiculopathy. Aim The aim of this study was to test the reliability of the spinal N22 potential in uncovering lesions of lumbosacral roots and its sensitivity verses DSEP and mixed somatosensory-evoked potential (MSEP). Patients and methods Fifty patients with a clinical suspicion of a lumbosacral root lesion were recruited. Twenty normal individuals constituted the control group to determine the cut-off points for the electrophysiological parameters. MRI of the lumbosacral spine was performed for all patients to detect lumbosacral root compression if present. For all patients, motor (peroneal and tibial nerves) and sensory (sural and superficial peroneal) nerve conduction studies were carried out in lower limbs using standard techniques. MSEP of the tibial nerve, DSEP studies of the affected lower limb, and spinal N22 SEP study of the tibial nerve were carried out. Results There was a positive correlation of statistical significance between the MSEP and the DSEP (P= 0.001) and between the MSEP and N22 (P= 0.001); however, there was a positive correlation of statistical significance between the DSEPs and the N22 (P = 0.001). There was a positive correlation of statistical significance between the MRI and the MSEP (P =0.004), the DSEP (P =0.001), and the N22 (P =0.002), respectively. The sensitivity and specificity of N22, DSEP, and MSEP were determined using MRI as a gold standard. N22 was the most sensitive (72.5%), followed by the DSEP (62.5%) and the least sensitive was the MSEP (42.5%). They were all specific (100%), with a high positive predictive value (100%). The N22 had the highest negative predictive value (47.6%), followed by the DSEP (40%), and the MSEP had the least negative predictive value (30%). Conclusion From this study, N22 was found to be a sensitive technique that is correlated with the MRI findings and is sensitive and specific with a high positive predictive value that is suitable for the diagnosis of early and minor cervical root lesions with manifest sensory complaints.

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