Urinary stress incontinence. A urodynamic and quantitative electromyographic study of the perineal muscles

Background. Neurophysiological techniques are increasingly used in examination of urinary incontinence. The purpose was to measure the activity in the perineal muscles in women with urinary stress incontinence and compare with normal subjects by using quantitative EMG methods. Methods. Twenty-four incontinent women and seven normal subjects were evaluated urodynamically and with quantitative EMG analysis of interference pattern and single fiber measurements. The recordings were made in the pubo rectal and the external anal sphincter muscle with empty urinary bladder at rest and maximal voluntary contraction as well as during cystometry. Results. The incontinent women had a denser interference pattern in the anal sphincter at rest but no differences at maximal activation compared to the reference group. No differences in interference pattern were noted between the two groups in the pubo rectal muscle. Fiber density in the external anal sphincter muscle was increased in the patient group (2.01 compared to 1.33, p<0.01). The urethral pressures at rest and activation were higher in the normal subjects (p<0.05). The normal subjects showed a denser interference pattern in the external anal sphincter muscle during cystometry (p<0.05). Conclusions. Quantitative analysis of the interference pattern and fiber density in the perineal muscles in incontinent women showed a denser interference pattern at rest and increased fiber density. Both observations indicate a peripheral nerve lesion. Furthermore, the interference pattern showed signs of reduced central activation in the incontinent women during cystometry.