Urethral sphincter needle electromyography in women: comparison of periurethral and transvaginal approaches

Needle electromyography (EMG) of the striated urethral sphincter is the only technique that permits detection of individual motor unit action potentials (MUAPs) and is a valuable diagnostic tool in the evaluation of women with urinary incontinence and voiding disorders. The purpose of this study was to compare two methods of urethral needle EMG with respect to the number of MUAPs identified, the amount of patient discomfort, and the duration of the examination. Twenty consecutive women referred for electrodiagnostic testing to evaluate symptoms of urinary incontinence and/or voiding dysfunction underwent both methods of the needle examination in a prospective randomized cross-over study design with each patient acting as her own control. A full cross-over analysis was conducted to detect period and sequence effects using analysis of variance with a power of 0.85 and a significance level of P < 0.05. Twice as many MUAPs were identified using the periurethral approach (8.8 versus 3.9) with a mean difference of 5.0 (P=0.0008). There was a non-significant trend to greater patient discomfort with the periurethral approach; however, the discomfort was generally rated as mild to moderate. The length of time required to count all identifiable MUAPs did not vary significantly between the two methods. We conclude that the periurethral approach is superior to the transvaginal approach with respect to the quantity of electrodiagnostic information obtained and propose that this method be standardized to characterize more accurately the neurogenic component of urinary incontinence and voiding dysfunction for future electrodiagnostic studies.