Neuromodulation of the lower urinary tract

For many years it has been known that peripheral electrical stimulation of the pudendal nerves through the skin or by implant can have a beneficial effect in the treatment of problems of the lower urinary tract, especially urinary incontinence caused by sphincter weakness or bladder overactivity (Thon et al. 1991; Fall & Madersbacher, 1994). This type of therapy seems to depend on a physiological process, commonly known as neuromodulation, in which the influence of activity in one neural pathway modulates the pre-existing activity in another through synaptic interaction. Little is known about the actual mechanisms underlying the success of this treatment in man, but some animal studies suggest a neurophysiological basis for neuromodulation (Fall & Lindstrom, 199 1). Many of the modulatory reflex mechanisms controlling normal continence are inhibitory in nature and have been shown to occur throughout the central and peripheral nervous systems involving a variety of neurotransmitter pathways (de Groat, 1997). It is probably aberrations in some of these pathways, for example, underactive inhibition at the brainstem level from more rostra1 cerebral structures or loss of descending inhibitory pathways to the sacral segmental reflexes, that causes bladder and sphincter dysfunction in the first place. Such dysfunction usually leads to incontinence. This paper focuses on those spinal and peripheral modulatory mechanisms that appear to be implicated in the pathophysiology of voiding dysfunction. It describes how applied neuromodulation of some specific peripheral pathways can help to overcome the incontinence resulting from these dysfunctions, especially bladder overactivity. It will also describe how neurostimulation is being used to investigate reflex pathways of the lower urinary tract in people both with and without bladder problems and the relevance of these studies in helping us to understand the aetiology of voiding dysfunction and the. physiological basis for its control by neuromodulation in man.