Histologic analysis of needle biopsy of urethral sphincter from women with normal and stress incontinence with comparison of electromyographic findings.

OBJECTIVE: Our goal was to compare urethral sphincter biopsy and needle electromyography between women who had genuine stress incontinence and those who did not. STUDY
DESIGN: Seventeen continent women and 10 women with stress incontinence had urethral sphincter needle electromyography and urethral biopsy specimens blindly processed for light and electron microscopy.
RESULTS: The continent group had greater skeletal muscle content and percentage in each muscle fascicle and each urethral sphincter. The group with genuine stress incontinence had higher connective tissue content. All urethral skeletal muscle was type 1. The smooth muscle was "multiunit" type and was morphologically indistinguishable between the 2 groups. On electromyography, patients with genuine stress incontinence had significantly more fibrillation potentials, fewer motor unit action potentials, a higher percentage of polyphasia, and less maximum voluntary electrical activity than control subjects.
CONCLUSIONS: Women with stress incontinence differ from continent women in skeletal muscle volume, amount of fibrosis, and electromyographic parameters; these differences support a neurogenic contribution to genuine stress incontinence. Urethral sphincter has only type 1 skeletal muscle and "multiunit" type smooth muscle.