Lumbar Spinal Stenosis: Diagnostic Value of Cauda Equina Motor Conduction Time at Rest and after Walk

Lumbosacral spinal stenosis is a narrowing of the spinal canal, which compresses the nerves travelling through the lower back into the lower limbs. Symptomatic patients often have intermittent neurogenic claudication, and with diagnostic procedures at rest, it is difficult to evaluate it objectively

Measurement of conduction in the cauda equine at rest and after walking may be a valuable tool in lumbosacral spinal stenosis work-up.

The aim of our study was to compare results of magnetic in electrical stimulation, and the peripheral motor conduction time. Methods: M and F waves and compound muscle action potentials were recorded after L1 MS, S1 MS, and L1 ES. Results: The compound muscle action potential latency on L1 MS was 26.9 ± 2.6 milliseconds and on L1 ES was 25.6 ± 2.2 milliseconds, and the peripheral motor conduction time was 27.0 ± 2.5 milliseconds (analysis of variance P = 0.0008). The compound muscle action potential amplitude was 12 ± 11% of M-wave on L1 MS, 32 ± 18% on S1 MS, and 31 ± 17% on L1 ES. Conclusions: Dorsal MS reliably elicits responses in the abductor hallucis muscle. The latency of compound muscle action potentials on L1 MS is comparable to peripheral motor conduction time. A potential drawback of MS may be too weak stimulation at the proximal end of the cauda equina.