A neurogenic element to urinary genuine stress incontinence.

The motor unit fibre density in the external anal sphincter has been measured in 35 women with genuine stress incontinence and in 14 continent women. The mean (SD) fibre density in the normal women was 1.5 (0.15) and in the incontinent women it was 1.96 (0.34) (P less than 0.002). These data provide evidence of peripheral denervation of the external anal sphincter and imply synchronous denervation of the pelvic floor muscles. It is suggested that denervation is an aetiological factor in genuine stress incontinence.