Studies of the mechanisms of sacral nerve stimulation for faecal incontinence: Investigations of anorectal and pelvic floor physiology and function

摘要

Studies of Sacral Nerve Stimulation (SNS) have demonstrated significant symptom improvement in Faecal Incontinence (FI); however, mechanisms of action remain poorly understood. Various authors have examined anorectal physiological parameters with SNS; and apart from an observed increase in squeeze pressures, findings were mostly inconsistent. It is currently believed that effects are mediated through neuromodulation. Identification of the involved neuronal pathways and the associated changes at the level of the target organ can further inform the process of patient selection for this costly treatment. The aim of this thesis was to examine potential SNS mechanisms by studying its effects on the sphincteric and suprasphincteric properties utilising physiological and structural tests. A total of 30 patients (29 female, median age 49 years) with intractable FI undergoing temporary SNS were recruited into four different studies designed to examine associated physiological and structural changes. The study of rectal properties revealed no change in rectal compliance following stimulation. However, rectal pressures associated with urge perception and maximally tolerated distension were significantly increased; predominantly in clinical responders. Anal squeeze pressures were significantly increased after stimulation in both responders and nonresponders. However, an increase in resting pressure was only noted in responders. Furthermore, Recto-Anal Inhibitory Reflex (RAIR) recovery time was significantly shorter after stimulation. An acute ON/OFF alteration of stimulation did not result in an acute change in anal pressures or RAIR parameters. Magnetic Resonance Proctography revealed a trend of reduced duration of rectal emptying after stimulation. Furthermore; it has suggested that more efficient contrast evacuation occurs after SNS. Mechanisms of SNS are most probably complex and multi-factorial. The observed changes in rectal sensory thresholds, RAIR recovery time and rectal evacuation in this study suggest that SNS influences the anorectal autonomic function and that it has an afferent-mediated mechanism.