Clinical application of spinal root neurograms for detection of conduction block in radiculopathy

In order to assess effects on conductivity of the spinal nerve roots which were compressed due to lumbar disc herniation (LDH) and spinal canal stenosis (SCS) at the lumbosacral vertebrae, spinal nerve root potentials (SRP) were recorded epidurally at multiple levels upon stimulation of the tibial and peronea nerves. Subjects were five normal volunteers and fifteen clinical cases (10 LDH and 5 SCS). Simultaneous recording of evoked EMGs was used to identify afferent and efferent components of SRPs. The shortest latency SRP consisted of orthodromic group I afferent and antidromic alpha-efferent potentials. The potential on liminal M-wave stimulation was regarded as representing exclusively group I volley and that on maximal M-wave stimulation as predominantly alpha-efferents. A centrifugally conducting nerve potential for H-reflex could be also recorded. Conduction blockage in the lumbar spinal roots of the clinical cases could be recognized as increased positivity and desynchronization. Quantitative assessment of these signs was devised in comparison to the control data. The present method revealed at least one of these signs in all clinical cases, and was found useful to determine the levels at which surgical decompression is indicated, supplementing radiological examination.