[Study of morphological changes in levator ani muscle of patients with stress urinary incontinence].

Objective: To observe the the histological changes of levator ani muscle in patients with stress urinary incontinence (SUI) or pelvic organ prolapse (POP) and to determine the alteration that contributed to pathogenesis.

Methods: Biopsy specimens of levator ani muscle were obtained from 15 patients with SUI, 19 patients with POP and 3 asymptomatic control with rectal cancer during operation. Levator ani muscle's structure was examined with routine histological techniques. At the same time, fiber distribution and diameters were also measured.

Results: The morphological features of levator ani muscle in SUI and POP group included the muscular fiber density decreased and separated by large amounts of dense connective tissue. The mean diameter of levator ani muscle in 4 SUI patients containing striated muscle fibers was (24 +/- 9) micro m, the mean diameter in 3 POP patients was (24 +/- 5) micro m, and the mean diameter in 3 control cases was (54 +/- 11) micro m. There was no diameter difference between SUI and POP group (P > 0.05), and the mean fiber diameters of SUI and POP patients were significantly smaller than that of the control group (P < 0.05). The proportion of type I fibers in SUI and POP patients had the tendency to increase (79.6%, 97.2% and 77.2%), with relative decrease of type II fibers. In control group the mean diameter of muscle fiber decreased significantly with age and menopausal time (P = 0.000).

Conclusions: There was obvious fibrosis and the muscle fiber atrophy in SUI and POP group, which resulted in the weakness of pelvic floor. The prevalence of type I fibers might be disadvantage to forceful contraction during straining. Aging also contributed to neuromuscular degeneration and then associated with urinary incontinence in elderly women.