Abstract:

Patients with cervical spondylosis commonly present to spinal surgeons with complex symptoms and imaging revealing degenerative change to multiple levels in the cervical spine.  Operating at multiple levels carries higher morbidity than single level surgery. Neurophysiologists are asked to see these referrals to identify the functionally worst level using the variety of tools at their disposal to try and limit the extent of surgery required.  NASS guidance reports the evidence for EMG alone is not high enough (1).

We are investigating a novel application for TMS MEPs which measures the conduction time through the cervical nerve roots and cervical cord; a simple non-invasive test for cervical cord and root function in diagnosing cervical myelo-radiculopathy. Our method utilises simultaneous 8-channel recording of compound muscle action potentials (CMAPs) in upper limb muscles corresponding to C5-T1 myotomes evoked by electrical stimulation of the brachial plexus.  The transradicular conduction time or axial conduction time is calculated by subtracting the latency of the peripheral response to stimulation of the brachial plexus from MEPs recorded from the same muscle.

In healthy controls (n=11) the axial conduction time is approximately constant in all upper limb muscles [mean latency 9ms (+/- 1ms SD)].  Using this normative dataset we audited clinical data from patients with cervical spondylosis who had previously had MEPs. 

Our preliminary analysis is promising and suggests that axial conduction time can identify abnormalities that are limited to specific root levels, and able to distinguish between myelopathy and radiculopathy, which has previously not been possible with TMS or EMG alone.