Magnetic stimulation of sacral roots for assessing the efferent neuronal pathways of lower urinary tract

The value of sacral magnetic stimulation (SMS) in neurophysiological evaluation of the sacral efferent pathways of the lower urinary tract was assessed during urodynamic examination in 10 men with chronic suprasacral spinal cord injury (SCI) and in 7 healthy volunteers. Investigated parameters included latency and amplitude of the urodynamic pressure response of the external urethral sphincter and detrusor to different stimulation strengths (50-100%) and single or repetitive (20 and 30 Hz) stimuli. Following SMS, reproducible external urethral sphincter pressure responses (mean latency, 13 ms) were recorded in all subjects. In contrast, a detrusor pressure increase was recorded only in SCI patients after repetitive SMS, with a latency of 1-2 s. This implies the appearance of a polysynaptic spinal reflex due to changes in organization of the sacral micturition reflex after SCI. The method of SMS may be helpful for the evaluation of cases in which urodynamic studies remain inconclusive.