Reversible prolongation of motor conduction time after transcranial magnetic brain stimulation after neurogenic claudication in spinal stenosis.

Study Design: A consecutive and controlled cohort study.

Objectives: To assess the value of motor conduction time (MCT) between cortex and symptomatic leg muscles after transcranial magnetic brain stimulation as an indicator of reversible root ischemia in patients with neurogenic claudication in spinal stenosis.

Summary Of Background Data: Neurogenic claudication in spinal stenosis is thought to result from transient ischemia of active nerve root fibers. Subgroups of these patients have slowing of sensory or motor nerve root conduction during spinal claudication.

Material And Methods: Forty-two patients with spinal claudication and radiologically confirmed signs of spinal stenosis were consecutively recruited. Motor conduction time was measured before and repetitively after challenge of walking on a treadmill (four stimuli per minute) until disappearance of the symptoms. Data of 30 patients (65 +/- 10 years) with a defined onset of motor-evoked potentials were compared with those of 12 control subjects (62 +/- 12 years).

Results: One minute after treadmill challenge, MCT increased in all 13 patients with signs of an exercise-dependent neurologic deficit by at least 1 msec (mean increase, 1.6 +/- 0.6 msec; < 0.001). Test-retest comparisons in six of these patients revealed good reproducibility of the MCT increase (coefficient of repeatability, 1.24 msec). In contrast, MCTs were unchanged or decreased in all 17 patients without exercise-dependent neurologic deficit ( < 0.01) and in the control subjects ( < 0.05).

Conclusions: Measurements of MCT before and after treadmill challenge can demonstrate reversible root ischemia in patients with spinal claudication and exercise-dependent deficit of thickly myelinated nerve root fibers.