7.1 Introduction

Pathologies affecting the central nervous system (CNS), despite obvious differences in terms of lesion level, etiology, and comorbidities, involve alterations of digestive functions and, in particular, defecation disorders [1, 2]. This is not surprising when considering that the ability to control bladder and bowel emptying is the last function that the Homo sapiens “cub” learns: children start walking and talking before being able of avoiding micturition and defecation at inappropriate times and before diaper weaning. Acquiring this ability means having the encephalic and medullary centers of both the CNS and the autonomic nervous system (ANS) well organized in order to control the same muscle-fascial structures of the abdominal wall and of the pelvic floor, so that they can first be effective at holding urine, feces and gas, and then efficient at expelling them at chosen times thus ensuring a complete emptying. It is therefore clear how even minor injuries of nerve pathways and control centers can easily compromise this integrated and delicate visceral, pelvic, and perineal dynamic. The pathophysiological mechanisms underlying intestinal dysfunctions on a neurogenic basis are a mix of different elements: reduced propulsion within the large intestine; abdominal-perineal dyssynergia due to deficiency and incoordination of pelvic floor muscles, associated with anorectal hyposensitivity; deficit of voluntary contraction of external anal sphincter; and abnormalities of internal sphincter reflex [3, 4]. There is ample literature that highlights how the management of intestinal evacuation is the most critical problem for people with CNS lesions once the acute phase is concluded, in terms of not only quality of life, but also morbidity and mortality [5, 6]. The term “neurogenic bowel” has been borrowed from bladder dysfunction, but there are many and significant differences between these two visceral disorders: while the level of the neurological lesion determines quite accurately which sequelae will be produced on bladder function (hyper-hypocompliant, hyper-hypoactive), this is not true for bowel, especially as regards intestinal motility. In the digestive tract wall lies a neuronal network which is comparable, in terms of number and complexity of cells and connections, to the brain, so much so that it is defined as a real “second brain,” which allows the bowel to have its own peristalsis even if totally isolated from CNS and ANS [7]. The most relevant difference regards the type of content that is evacuated from the two organs: liquid from the bladder, from semiliquid to decidedly solid from the bowel. Moreover, the flow of urine is constant towards the bladder, while the filling of rectum (which is physiologically empty outside the defecatory event) shows great differences in terms of content volume and time for occurring. The fecal volume, in addition to water percentage, is determined by the presence of bacteria originating from the colon microflora [8]. The colon represents a real ecosystem with a concentration of microorganisms that has no equal in any other habitat on the planet Earth. Indeed, more than 1000 different bacterial groups live in the human intestine and form a biomass that can weigh up to 1.5 kg and has a huge (and mostly still unknown) metabolic activity: a sort of second liver made up of 100,000 billion prokaryotic cells [9]. It should be noted that the action of fibers and prebiotics is not due to a “mass” effect resulting from a recall of water produced by the polysaccharide molecules of which they are made up, but their action, which favors evacuation, derives from the fact that they constitute the main metabolic substrate for the colon microflora: the biomass grown this way constitutes 60–80% of the dry weight of the feces. It follows that the primary objective of intestinal rehabilitation, in a patient who has lost control and efficiency of evacuation mechanisms due to a CNS damage, is certainly to achieve defecation but not “di per sè,” but as a way of rebalancing the ecosystem in the intestinal lumen [10]. Since it is often impossible to retrieve a physiological evacuation (as it is the case of micturition too), it is necessary to adopt methods for programming intestinal emptying, which could guarantee completeness and adequate times and, in the long run, are not detrimental to the anorectal region.

7.2 Objectives of Intestinal Rehabilitation in the Person with CNS Lesions

Contrary to what could be assumed, recovering a bowel evacuation as it was before the damaging event, that is spontaneous and following the perception of a “defecation need” signal, is not a primary rehabilitation goal: it is often impossible and it almost always exposes the patient to the risk of incontinence and incomplete emptying.

7.3 Tools for Assessment and Monitoring of Bowel Dysfunction