Reference Data of Cervical Dermatomal Somatosensory Evoked Potentials Using Low Intensity Stimulation and Report of 2 Cases

OBJECTIVE: To establish reference data for dermatomal somatosensory evoked potentials (DSEP) using a stimulation intensity lower than what is conventionally utilized. METHOD: Fifty subjects (25 older adults>48 years old; 25 younger adults<32 years old) without history of neck pain or cervical spine surgery were enrolled. The DSEP study was performed with stimulation intensities of 1.0, 1.5, and 2.5 times sensory threshold (ST) on right arms for C5, C6, C7, and C8 dermatomes. RESULTS: The mean latencies of DSEP stimulating C5, C6, C7, and C8 dermatomes with 1.5 times ST intensity were 17.6+/-1.7 ms, 22.2+/-2.1 ms, 22.8+/-1.4 ms, and 22.6+/-1.8 ms, respectively. The mean amplitude (N1P1) of DSEP stimulating C5, C6, C7, and C8 dermatomes with 1.5 times ST intensity were 0.9+/-0.4 microV, 0.9+/-0.5 microV, 1.0+/-0.6 microV, and 1.1+/-0.8 microV, respectively. The C5, C6, C7, and C8 DSEP were evoked in 84%, 98%, 100%, and 96% of cases with 2.5 times ST compared to 64%, 56%, 60%, and 62% with 1.5 times ST, respectively. When one DSEP was not evoked, the DSEP of the opposite side was evoked only in 2 subjects. CONCLUSION: This study provides the reference data of DSEP with lower stimulation intensities than are conventionally utilized. Additionally, two cases of clinical significance were reported.

Determination of Neurological Impairment Level in Thoracic SpinalCord Injuries using Dermatomal Somatosensory Evoked Potentials

OBJECTIVE: To determine sensory levels of injury using dermatomal somatosensory evoked potentials (SEPs) and compare with the neurological level of injury determined by ASIA standard in patients with thoracic spinal cord injury. METHOD: By stimulating segmental thoracic dermatomes, cortical SEPs were studied in nine spinal cord injured patients from T2 to T12 (9 men, mean age 41.8) and 20 normal adult men (mean age, 28.3). The SEP studies were performed bilaterally. RESULTS: In eight cases (44%) of the paraplegics tested, the neurological level of injury by dermatomal SEPs was same compared to the level of injury assessed by ASIA standard. In 15 cases (83%), there were no or one level difference of the level of injury between the levels by SEPs and ASIA standard. CONCLUSION: This study suggests that dermatomal SEP can be a useful tool in determination of the neurological level of injury in patients with thoracic spinal cord injury.

Diagnostic Usefulness of Dermatomal Somatosensory Evoked Potentials by Low Intensity Stimulation in Lumbar Radiculopathy

OBJECTIVE: To investigate diagnostic usefulness of dermatomal somatosensory evoked potentials (DSEP) in the evaluation of lumbar radiculopathy using stimulation intensity lower than conventional stimulation intensity. METHOD: Fifty-seven patients with low back pain were studied with DSEP and needle electromyography (EMG). The radiculopathy was diagnosed by lumbar MRI or operative findings. The DSEP study was performed with stimulation intensity of 1.0x, 1.5x, 2.5x sensory threshold, respectively. We compared the sensitivity and specificity of DSEP and needle EMG in the evaluation of L5 radiculopathy. RESULTS: Radiological and operative findings revealed unilateral herniated disc and L5 root compression in 38 patients (66.7%). Nineteen patients had no significant L5 root compression. The sensitivity and specificity of abnormality were 68.4% and 78.9% in 1.0x sensory threshold stimulation; 71.1%, 78.9% in 1.5x sensory threshold stimulation; and 44.7%, 84.2% in 2.5x sensory threshold stimulation, respectively. Whereas they were 55.2% and 100% in needle EMG. CONCLUSION: DSEP using low stimulus intensity showed higher sensitivity in the diagnosis of L5 radilculopathy, and DSEP might provide additional diagnostic usefulness in the evaluation of patients with suspected L5 radiculopathy.

The Value of the Dermatomal Somatosensory Evoked Potentials in Patients with Lumbosacral Radiculopathy

OBJECTIVE: The purposes of this study were to evaluate the diagnostic value of dermatomal somatosensory evoked potentials (DSEPs) in the unilevel/unilateral lumbosacral radiculopathies. METHOD: The study was performed on 41 patients with herniated lumbosacral disc which was confirmed by magnetic resonance imaging, and the patients with clinical lumbosacral radiculopathies (L5 radiculopathy in 33 cases and S1 radiculopathy in 8 cases). Stimulation sites were over the dorsum of the foot on the distal fifth metatarsal bone for the S1 dermatome and at the interdigital web space between first and second toe for the L5 dermatome. Recordings were made at Cz' and reference to Fz. Conventional nerve conduction study, needle EMG and H-reflex were also examined. RESULTS: While the needle EMG showed abnormalities in 32 patients (78.0%), the abnormalities of DSEPs were in 13 patients (31.7%): 33.3% for the L5 radiculopathy and 25.0% for the S1 radiculopathy, respectively. Moreover, there was no significant relationship between the abnormal findings of needle EMG and DSEPs (p>0.05). The H-reflexes were abnormal in 6 of 7 patients (85.7%). And then two of them were found abnormal in S1 DSEPs. CONCLUSION: The conventional needle EMG appears to be the more useful electrophysiological technique in the diagnosis of lumbosacral radiculopathies. The ultimate diagnostic value of DSEPs in lumbosacral radiculopathies is doubtful and controversial.