Evidence of electromechanical dissociation of the internal anal sphincter in idiopathic fecal incontinence

Spontaneous Internal Anal Sphincter Relaxation During High-resolution Anorectal Manometry Is Associated With Peripheral Neuropathy and Higher Charlson Comorbidity Scores in Patients With Defecatory Disorders

Background/Aims

We aimed to evaluate associations between comorbidities, peripheral neuropathy, and spontaneous internal anal sphincter relaxation (SAR) in patients with defecatory disorders.

Methods

A patient was considered to exhibit SAR during high-resolution anorectal manometry (HR-ARM) when the nadir pressure is < 15 mmHg and the time from onset to relaxation was ≥ 15 seconds in the resting pressure frame. A case-control study was performed using HR-ARM data collected from 880 patients from January 2010 to May 2015. We identified 23 cases with SAR (median age 75 years; 15 females; 12 fecal incontinence and 11 constipation). We compared HR-ARM values, Charlson index comorbidity scores, neuropathy, and the prevalence of diseases that potentially cause neuropathy between controls and SAR patients. Each SAR case was compared to 3 controls. Controls were selected to match the age, gender, and examination year of each SAR case.

Results

Compared to controls (26.1%), SAR patients (52.2%) exhibited a significantly higher frequency of fecal incontinence. SAR patients also had higher Charlson index scores (5 vs 4, P = 0.028). Nine of 23 SAR patients (39.1%) exhibited peripheral neuropathy— this frequency was higher than that for the control group (11.6%; P = 0.003). Diseases that potentially cause neuropathy were observed in 17 of 23 SAR cases and 32 of 69 controls (P = 0.022).

Conclusions

SAR develops in patients with constipation and fecal incontinence but is more common in patients with fecal incontinence. Our controlled observational study implies that SAR is associated with peripheral neuropathy and more severe comorbidities.

Manometric, sensorimotor, and neurophysiologic evaluation of anorectal function

With advances in diagnostic technology, it is now accepted that in the field of functional bowel disorders, symptom-based assessment is unsatisfactory as the sole means of directing therapy. A robust taxonomy based on underlying pathophysiology has been suggested, highlighting a crucial role for physiologic testing in clinical practice. A wide number of complementary investigations currently exist for the assessment of anorectal structure and function, some of which have a clinical impact in patients with functional disorders of evacuation and continence by markedly improving diagnostic yield and altering management. The techniques, limitations, measurements, and clinical use of manometric, sensorimotor, and neurophysiologic tests of anorectal function are presented.

Stress, Urge, and Mixed Types of Partial Fecal Incontinence: Pathogenesis, Clinical Presentation, and Treatment

The authors investigated the hypothesis that partial fecal incontinence (PFI) had variable manifestations that can be categorized as different types of PFI with different pathogeneses and treatment. Anal and rectal pressures as well as external and internal anal sphincter electromyographic activity were recorded in 163 patients with PFI and in 25 healthy volunteers. Patients were treated with biofeedback or surgically. Three types of PFI were encountered: stress fecal incontinence (SFI; 55 patients), urge fecal incontinence (UFI; 72 patients), and mixed fecal incontinence (MFI; 36 patients). Anal pressure decreased in three groups in which MFI had the lowest pressure. A significant reduction in external anal sphincter electromyographic activity occurred in SFI, in internal anal sphincter electromyographic activity in UFI, and of both sphincters in MFI. Bio-feedback cured 36 of 55 patients and postanal repair cured 10 of 19 patients with SFI. Forty-eight of 72 patients with UFI responded to biofeedback and 16 of 24 responded to internal anal sphincter repair. Biofeedback failed in MFI patients. Twenty-four of 27 patients who consented to operative correction of the sphincteric defect were cured. Three types of PFI could be identified: SFI, UFI, and MFI. Each type has its own etiology and symptoms, and requires individual treatment. Biofeedback succeeded in treating the majority of SFI and UFI patients. Surgical correction of the anal sphincter was performed after biofeedback failure.

Neurophysiological testing in anorectal disorders

The neurophysiological techniques currently available to evaluate anorectal disorders include concentric needle electromyography (EMG) of the external anal sphincter, anal nerve terminal motor latency (TML) measurement in response to transrectal electrical stimulation or sacral magnetic stimulation, motor evoked potentials (MEPs) of the anal sphincter to transcranial magnetic cortical stimulation, cortical recording of somatosensory evoked potentials (SEPs) to anal nerve stimulation, quantification of electrical or thermal sensory thresholds (QSTs) within the anal canal, sacral anal reflex (SAR) latency measurement in response to pudendal nerve or perianal stimulation, and perianal recording of sympathetic skin responses (SSRs). In most cases, a comprehensive approach using several tests is helpful for diagnosis: needle EMG signs of sphincter denervation or prolonged TML give evidence for anal motor nerve lesion; SEP/QST or SSR abnormalities can suggest sensory or autonomic neuropathy; and in the absence of peripheral nerve disorder, MEPs, SEPs, SSRs, and SARs can assist in demonstrating and localizing spinal or supraspinal disease. Such techniques are complementary to other methods of investigation, such as pelvic floor imaging and anorectal manometry, to establish the diagnosis and guide therapeutic management of neurogenic anorectal disorders.

Internal anal sphincter: advances and insights

The internal anal sphincter, the smooth muscle component of the anal sphincter complex, has an ambiguous role in maintaining anal continence. Despite its significant contribution to resting anal canal pressures, even total division of the internal anal sphincter in surgery for anal fistulas may fail to compromise continence in otherwise healthy subjects. However, recently reported abnormalities of the innervation and reflex response of the internal anal sphincter in patients with fecal incontinence indicate its significance in maintaining continence. The advent of sphincter-saving surgery and restorative proctocolectomy has re-emphasized the major contribution of the internal anal sphincter to resting pressure and its significance in preventing fecal leakage. The variable effect of rectal excision on rectoanal inhibitory reflex has led to a reappraisal of the significance of this reflex in discrimination of rectal contents and its impact on anal continence. Electromyographic, manometric, and ultrasonographic evaluation of the internal anal sphincter has provided new insights into its pathophysiology. This article reviews advances in our understanding of internal anal sphincter physiology in health and disease.

Sustained internal sphincter hypertonia in patients with chronic anal fissure

PURPOSE

This study was designed to determine whether functional variations of internal sphincter activity occur in order to differentiate between patients with anal fissures from those with hemorrhoids.

METHODS

Thirty patients with chronic anal fissure (median age, 28 years; 12 females), 22 patients with hemorrhoids (median age, 37 years; 7 females), and 33 control volunteers (median age, 48.5 years; 21 females) underwent ambulatory anal sphincter fine-needle electromyography and anorectal manometry.

RESULTS

The median internal sphincter electromyography frequency was similar: fissure group, 0.49 Hz; hemorrhoid group, 0.46 Hz (P > 0.05), and control group, 0.44 Hz (P > 0.05). Median anal resting pressures were similar in the fissure group (132 cm. H2O) and the hemorrhoids group (116 cm of H2O) (P > 0.05), but significantly greater than those in the control group (94 cm. H2O) (P < 0.05). The median number of transient relaxations of the internal and sphincter with an associated rise in rectal pressure and fall in anal pressure was 1 (range, 0-4) per hour in the fissure group, 6 (range, 4-7) per hour in the hemorrhoid group, and 4 range, 3-6) per hour in the control group. Six patients with fissures were reassessed following lateral internal sphincterotomy. Median and pressure was 102 cm of H2O (P > 0.1 vs. controls) and the number of internal sphincter relaxations increased to 4 per hour (P < 0.01 vs. preoperative number).

CONCLUSIONS

Internal anal sphincter relaxation occurs on fewer occasions in patients with chronic anal fissures that have failed to heal in comparison to patients with hemorrhoids and normal controls. This evidence further supports the hypothesis that internal sphincter hypertonia may be relevant to the pathogenesis of this disorder.