The perspective of a neurologist on treatment-related research in fecal and urinary incontinence.

Afferent innervation is important in sensing the degree of bladder fullness and in forming the input limb to involuntary detrusor contractions in neurogenic and probably also non-neurogenic detrusor overactivity. It is likely that homologous mechanisms are involved in control of the bowel. Accumulating evidence now suggests that in conditions of bladder hypersensitivity as well as non-neurogenic detrusor overactivity, there is up-regulation of unmyelinated nerve fibers expressing both the vanilloid receptor and purinergic receptors. The development of a selective neurotoxin that could successfully "deafferent" the bladder would have major therapeutic consequences. Women who respond best to neuromodulation through sacral nerve stimulation are those with a primary disorder of sphincter relaxation and a very large capacity without sensations of urgency or a hyperactive sphincter. For these women, neuromodulation may counteract the inhibitory effects of overactive sphincter afferents on the detrusor, and determination of the central nervous system level at which this response occurs may provide an explanation for the paradoxical finding that both urge incontinence and urinary retention are responsive to this intervention. Experimental evidence suggests that the "procontinence" reaction consists of an inhibitory effect on the detrusor and presumably the lower rectum resulting from contraction of the pelvic floor and the anal or urethral sphincter. Development of methods of enhancing the inhibitory reflex effect could lead to improved voluntary control of micturition and defecation for patients with neurogenic bladder overactivity or spinal cord lesions.