Denervation and re-innervation of the urethral sphincter in the aetiology of genuine stress incontinence: an electromyographic study.

OBJECTIVE

To investigate the role of altered innervation of the urethral sphincter in the genesis of genuine stress incontinence.

DESIGN

Prospective observational study.

SETTING

Tertiary referral centre urodynamics unit.

SUBJECTS

Sixty-eight women, 33 with urodynamically proven pure genuine stress incontinence and 35 controls without urinary symptoms.

INTERVENTIONS

Concentric needle electromyography of the urethral striated sphincter.

MAIN OUTCOME MEASURES

The means of motor unit potential duration, number of changes in polarity and the amplitude of individual motor unit potentials were compared between the two groups.

RESULTS

There was no statistically significant difference in motor unit potential duration (P = 0.87) or in the number of changes in polarity (P = 0.85). There was a trend towards a higher amplitude of motor unit potentials in the control group (P = 0.07).

CONCLUSIONS

Our findings suggest that denervation and re-innervation of the striated urethral sphincter following trauma to the pelvic floor, such as that occurring during childbirth, is not a major aetiological factor in the development of genuine stress incontinence.