Modulation of the rectoanal inhibitory reflex (RAIR): qualitative and quantitative evaluation in multiple sclerosis

Abstract

Rectoanal inhibitory reflex (RAIR) is a physiological modulated reflex involved in anorectal continence and defined by a relaxation of internal anal sphincter following rectal distension. Its existence depends on intramural autonomic ganglions and its modulation on the integrity of the autonomic nervous system (ANS). The aim of this study was to analyse RAIR modulation in terms of amplitude and duration in multiple sclerosis (MS) patients. Twenty-one patients with MS and 40 control patients had anorectal manometry. Qualitative assessment (presence or absence) of RAIR was evaluated together with its modulation in amplitude and in duration. All patients had present RAIR for each volume of rectal distension (10-50 ml). Seven patients (33.3%) in the MS group had abnormal RAIR modulation in amplitude (odds ratio (OR) = 2.78, compared to control group, p = 0.11). Nine patients (42.9%) in the MS group had abnormal RAIR modulation in duration (p = 0.14, OR = 2.54, compared to control group). Alteration of RAIR modulation was not correlated with Expanded Disability Status Scale, faecal incontinence and constipation (p > 0.05). Course of MS (relapsing-remitting MS or secondary progressive form) seems to be correlated to alteration of modulation in amplitude and in duration (OR = 1.31 and 1.07). Even if our results do not have the required statistical significance (p > 0.05), they are interesting. If RAIR is always present in MS, its modulation seems to be altered. A hypothesis for this lack of RAIR modulation could be the alteration of ANS, often involved in MS besides somatic nervous system lesions.