Individual motor unit analysis in the diagnosis of disorders of urethral sphincter innervation.

A technique is described for recording the electromyographic activity of striated muscle in the urethral sphincter. Using a concentric needle electrode and an oscilloscope with a delay line and trigger, individual motor units were isolated and measured. To validate the method as a means of detecting pathology, the results are presented of analysis of the motor units of a group of patients with disturbances of micturition, known to have either cauda equina lesions or pelvic nerve injury. These results are compared with those from a group of controls. In the control group 93% of the motor units were less than 6 ms in duration and 2.0 mv in amplitude. Of motor units recorded from patients with cauda equina or pelvic nerve injury 59% exceeded the control ranges for amplitude or duration. It is concluded that quantitative analysis of individual motor units may be a helpful technique in the investigation of patients with disorders of micturition.