Incontinence of urine due to instability of micturition reflexes. Part II. Pudendal nucleus instability.

Overinhibition or underfacilitation of the pudendal nucleus may cause profound involuntary relaxation of the striated muscles of the pelvic floor and perineum, including the "external" striated urethral sphincter. Pudendal nucleus instability may adversely affect urethral closure pressure and preclude a successful voluntary "recovery" effort to limit stress incontinence. It may also result in the involuntary loss of an important source of inhibition to the sacral micturition reflex center, which can lead to detrusor instability. The bilateral reciprocal relationship which exists between the detrusor reflex and the pelvic floor muscle tonus is fundamental to micturition instability syndromes. In this article, the pathophysiology of interaction of pudendal nucleus instability, detrusor reflex instability, and stress is described, and the importance of careful diagnostic evaluation of each case of incontinence is emphasized.