Magnetoneurographic 3D localization of conduction blocks in patients with unilateral S1 root compression

Objectives: Tibial nerve somatosensory evoked magnetic fields (tSEFs) over the lower back reflect the propagation of compound action currents along fibers of plexus, nerve roots and cauda equina. One clinical perspective for this `magnetoneurography' is the non-invasive 3D localization of focal slowing or blocks of conduction. Here, first tSEF mappings in 3 consecutive patients with acute unilateral S1 nerve root compression are reported.

Methods: Right and left tibial nerves were electrostimulated in alternation; tSEF responses were recorded using a multichannel SQUID-detector; additionally, spinal and cortical SEP, F-wave and H-reflex studies were performed.

Results: In all patients an intraindividual side-to-side comparison of spinal tSEF mappings was obtained: using a dipolar source model compound action, currents could be visualized propagating along plexus, nerve roots and cauda equina on the non-affected side whereas on the affected side normally-propagating dipolar field patterns could be recorded only distal to the spinal transforaminal root entrance; this reflects focal slowing or block of conduction in nerve root fibers as indicated by the SEP, F-wave and H-reflex study results.

Conclusion: With a registration time of 15 min a 3D localization of proximal slowing or block of conduction was successfully performed in patients suffering from acute nerve root lesions.