Abnormal neuronal response to rectal and anal stimuli in patients with idiopathic fecal incontinence

The new measures of interoceptive accuracy: A systematic review and assessment

Conscious interoception, the perception of internal bodily states, is thought to contribute to fundamental human abilities (e.g., decision-making and emotional regulation). One of its most studied dimensions is interoceptive accuracy: the objective capacity to detect internal bodily signals. In the past few years, several labs across the world have started developing new tasks aimed at overcoming limitations inherent in classical measures of interoceptive accuracy. In this systematic review, we identified these tasks (since 2015) for the cardiac, respiratory, and gastrointestinal domains. For each identified task, we discuss their strengths and weaknesses, and make constructive suggestions for further improvement. In the general discussion, we discuss the (potentially elusive) possibility of reaching high validity in the measurement of interoceptive accuracy. We also point out that interoceptive accuracy may not be the most critical dimension for informing current theories, and we encourage researchers to investigate other dimensions of conscious interoception.

Parieto-occipital ERP indicators of gut mechanosensation in humans

Understanding the neural processes governing the human gut-brain connection has been challenging due to the inaccessibility of the body's interior. Here, we investigated neural responses to gastrointestinal sensation using a minimally invasive mechanosensory probe by quantifying brain, stomach, and perceptual responses following the ingestion of a vibrating capsule. Participants successfully perceived capsule stimulation under two vibration conditions (normal and enhanced), as evidenced by above chance accuracy scores. Perceptual accuracy improved significantly during the enhanced relative to normal stimulation, which was associated with faster stimulation detection and reduced reaction time variability. Capsule stimulation induced late neural responses in parieto-occipital electrodes near the midline. Moreover, these 'gastric evoked potentials' showed intensity-dependent increases in amplitude and were significantly correlated with perceptual accuracy. Our results replicated in a separate experiment, and abdominal X-ray imaging localized most capsule stimulations to the gastroduodenal segments. Combined with our prior observation that a Bayesian model is capable of estimating computational parameters of gut-brain mechanosensation, these findings highlight a unique form of enterically-focused sensory monitoring within the human brain, with implications for understanding gut feelings and gut-brain interactions in healthy and clinical populations.

The PanGut-study: Evoked potentials following rectal balloon distention, a way of evaluating diabetic autonomic neuropathy in the gut?

AIM

There is a lack of methods for investigating the autonomic nerves of the gastrointestinal tract. Our aim was to explore a novel test measuring visceral sensory evoked potentials (EPs) in response to rapid balloon distention in the rectum and compare it to established tests for diabetic neuropathy.

METHOD

Participants with longstanding type 2 diabetes, newly onset, untreated diabetes <1 year, and matched controls, were included. Tests included cardiovascular reflex tests, orthostatic blood pressure, electrical skin conductance assessment, sural nerve testing and monofilament test. The rectal balloon distention pressure at earliest sensation and threshold of unpleasantness were identified and used to elicit mechanical EPs.

RESULTS

The pressure at earliest sensation was higher in people with diabetes, 0.038 (0.012) bar vs. controls 0.030 (0.009) bar, p = 0.002, and in people with signs of peripheral neuropathy, 0.045 (0.014) bar, p < 0.01. Clinical correlations between EP amplitude and latency, and other tests were found.

CONCLUSIONS

Rectal hyposensitivity was associated with both longstanding and early diabetes, indicating enteric sensory dysfunction already in early stages of diabetes. Correlation analyses may indicate that central afferent processing is affected in parallel with peripheral neuronal function.

Abnormal Neuronal Response to Rectal and Anal Stimuli in Patients Treated for Distal Rectal Cancer With High-Dose Chemoradiotherapy Followed By Watchful Waiting

BACKGROUND

Watchful waiting in patients with rectal cancer with complete clinical response after chemoradiation therapy has gained increased popularity to avoid morbidity and mortality associated with surgery. Irradiation of the pelvis causes bowel dysfunction, but the effect on anorectal sensory function remains obscure in this patient category.

OBJECTIVE

The aim of this study was to characterize the sensory pathways of the gut-brain axis in patients with rectal cancer treated solely with chemoradiation therapy (nonconventional regime/dose) compared with healthy volunteers.

DESIGN

This is an explorative study.

SETTINGS

Sensory evaluation by rectal distension was performed and cortical evoked potentials were recorded during rapid balloon distensions of the rectum and anal canal. Latencies and amplitudes of cortical evoked potentials were compared, and the relative amplitude of 5 spectral bands from recorded cortical evoked potentials was used as an additional proxy of neuronal processing.

PATIENTS

Patients with rectal cancer solely with chemoradiation therapy (n = 13) a median of 3.2 years ago (range, 2.3-5.6 y) and healthy volunteers (n = 13) were included.

MAIN OUTCOME MEASURES

Cortical evoked potentials were measured.

RESULTS

Patients had 35% lower rectal capacity at a maximum tolerable volume (p = 0.007). We found no differences in rectal cortical evoked potential latencies (p = 0.09) and amplitudes (p = 0.38) between groups. However, spectral analysis of rectal cortical evoked potentials showed a decrease in θ (4-8 Hz) and an increase in β (12-32 Hz) band activity in patients (all p < 0.001). Anal cortical potentials showed an increase in α (8-12 Hz) and β and a decrease in γ (32-70 Hz) band activity (all p < 0.001) in patients compared with healthy volunteers.

LIMITATIONS

This is an explorative study of limited size.

CONCLUSIONS

Chemoradiation therapy for distal rectal cancer causes abnormal cortical processing of both anal and rectal sensory input. Such central changes may play a role in symptomatic patients, especially when refractory to local treatments. See Video Abstract at http://links.lww.com/DCR/B270. RESPUESTA NEURONAL ANORMAL A ESTÍMULOS RECTALES Y ANALES, EN PACIENTES TRATADOS POR CÁNCER RECTAL DISTAL, CON QUIMIORRADIOTERAPIA DE DOSIS ALTA, SEGUIDA DE ESPERA VIGILANTE: La espera vigilante en pacientes de cáncer rectal, con respuesta clínica completa después de la quimiorradiación, ha ganado una mayor popularidad en evitar la morbilidad y mortalidad asociadas con la cirugía. La irradiación de la pelvis causa disfunción intestinal, pero el efecto sobre la función sensorial ano-rectal sigue siendo no claro, en esta categoría de pacientes.El objetivo de este estudio, fue caracterizar las vías sensoriales del eje intestino-cerebro en pacientes con cáncer rectal, tratados únicamente con quimiorradiación (régimen / dosis no convencional), en comparación con voluntarios sanos.Es un estudio exploratorio.Se realizó una evaluación sensorial por distensión rectal y se registraron los potenciales evocados corticales, durante las distensiones rápidas con balón en recto y canal anal. Se compararon las latencias y amplitudes de los potenciales evocados corticales, y la amplitud relativa de cinco bandas espectrales registradas, de potenciales evocados corticales, se usaron como proxy adicional del procesamiento neuronal.Pacientes de cáncer rectal, únicamente con terapia de quimiorradiación (n = 13) mediana de 3.2 años (rango 2.3-5.6) y voluntarios sanos (n = 13).Potenciales evocados corticales.Pacientes tuvieron una capacidad rectal menor del 35%, al volumen máximo tolerable (p = 0.007). No encontramos diferencias en las latencias potenciales evocadas corticales rectales (p = 0.09) y amplitudes (p = 0.38) entre los grupos. Sin embargo, el análisis espectral de los potenciales evocados corticales rectales, mostró una disminución en theta (4-8 Hz) aumento en beta (12-32 Hz), y actividad en banda en pacientes (todos p <0.001). Los potenciales evocados corticales anales mostraron un aumento en alfa (8-12 Hz) y beta, disminución en gamma (32-70 Hz), y actividad en banda (todos p <0.001), en pacientes comparados a voluntarios sanos.Este es un estudio exploratorio de tamaño limitado.La quimiorradiación para el cáncer rectal distal, ocasiona procesos corticales sensoriales anormales anales y rectales. Tales cambios centrales pueden desempeñar un papel en pacientes sintomáticos, especialmente cuando son refractarios a tratamientos locales. Consulte Video Resumen en http://links.lww.com/DCR/B270.

Sacral Nerve Modulation Has No Effect on the Postprandial Response in Irritable Bowel Syndrome

Purpose

Irritable bowel syndrome is a common gastrointestinal disorder with a global prevalence of approximately 11%. Onset or worsening of symptoms following digestion is one of the characteristics of the condition. The present study aimed at evaluating the postprandial sensory and motor response before and after treatment with sacral nerve modulation.

Patients and Methods

Twenty-one irritable bowel syndrome patients, 12 diarrhea-predominant and 9 mixed, were eligible for a 6-week sacral nerve modulation test period. Patients were investigated with multimodal impedance planimetry including a standardized meal at baseline and at the end of 2 weeks of suprasensory stimulation embedded in the 6-week sacral nerve modulation period.

Results

There was no statistical significant difference in the sensory response to heat or cold before and after sacral nerve modulation, p>0.05. At baseline, wall tension increased after the meal (mean 124.79 [range 82.5 to 237.3] mmHg.mm before the meal, mean 207.76 [range, 143.5 to 429] mmHg.mm after the meal), p=0.048 indicating a postprandial response. During sacral nerve modulation, the postprandial increase in wall tension did not reach statistical significance (mean 86.79 [range 28.8 to 204.5] mmHg.mm before the meal, mean 159.71 [range 71.3 to 270.8] mmHg.mm after the meal), p=0.277. However, there was no statistically significant difference between the postprandial wall tension at baseline and during sacral nerve modulation, p=0.489. Likewise, we found no difference between pressure or stretch ratio at baseline and during sacral nerve modulation, p>0.05.

Conclusion

Sacral nerve modulation does not exert its positive treatments effects in diarrhea-predominant and mixed irritable bowel syndrome through a modulation of the postprandial response.

Cortical processing to anorectal stimuli after rectal resection with and without radiotherapy

BACKGROUND

Bowel dysfunction is common after surgery for rectal cancer, especially when neoadjuvant radiotherapy is used. The role of sensory function in the pathogenesis remains obscure, and the aim of the present study was to characterize the sensory pathways of the brain-gut axis in rectal cancer patients treated with resection ± radiotherapy compared with healthy volunteers.

METHODS

Sensory evaluation by (neo)rectal distensions was performed and sensory evoked potentials (SEPs) were recorded during rapid balloon distensions of the (neo)rectum and anal canal in resected patients with (n = 8) or without (n = 12) radiotherapy. Twenty healthy volunteers were included for comparison. (Neo)rectal latencies and amplitudes of SEPs were compared and spectral band analysis from (neo)rectal and anal distensions was used as a proxy of neuronal processing.

RESULTS

Neorectal sensation thresholds were significantly increased in both patient categories (all p < 0.008). There were no differences in (neo)rectal SEP latencies and amplitudes between groups. However, spectral analysis of (neo)rectal SEPs showed significant differences between all groups in all bands (all p < 0.01). On the other hand, anal SEP analyses only showed significant differences between the delta (0-4 Hz), theta (4-8 Hz) and, gamma 32-50 Hz) bands (all p < 0.02) between the subgroup of patients that also received radiotherapy and healthy volunteers.

CONCLUSIONS

Surgery for rectal cancer leads to abnormal cortical processing of neorectal sensation. Additional radiotherapy leads to a different pattern of central sensory processing of neorectal and anal sensations. This may play a role in the functional outcome of these patients.

Assessment of brain activity during voluntary anal sphincter contraction: Comparative study in women with and without fecal incontinence

BACKGROUND

Voluntary anal sphincter function is driven by an extended network of brain structures, most of which are still unknown. Disturbances in this function may cause fecal incontinence. The aim of this study was to characterize the cerebral areas involved in voluntary contraction of the anorectal sphincter in healthy women and in a group of patients with fecal incontinence by using a standardized functional magnetic resonance imaging (fMRI) protocol.

METHODS

This comparative study included 12 healthy women (mean age 53.17 ± 4.93 years) and 12 women with fecal incontinence (56.25 ± 6.94 years). An MRI-compatible anal manometer was used to register voluntary external anal sphincter contraction. During brain fMRI imaging, participants were cued to perform 10-s series of self-paced anal sphincter contractions at an approximate rate of 1 Hz. Brain structures linked to anal sphincter contractions were mapped and the findings were compared between the 2 study groups.

KEY RESULTS

There were no differences in the evoked brain activity between the 2 groups. In healthy women, group fMRI analysis revealed significant activations in medial primary motor cortices, supplementary motor area, bilateral putamen, and cerebellum, as well as in the supramarginal gyrus and visual areas. In patients with fecal incontinence, the activation pattern involved similar regions without significant differences with healthy women.

CONCLUSIONS & INFERENCES

This brain fMRI-anorectal protocol was able to map the brain regions linked to voluntary anal sphincter function in healthy and women with fecal incontinence.

Human studies of anorectal sensory function

This review addresses three main questions: (1) Why is anorectal sensory function important in humans? (2) What is the evidence for anorectal sensory dysfunction in disease? (3) Can anorectal sensory function be modified for therapeutic benefit?

Microstructural white matter brain abnormalities in patients with idiopathic fecal incontinence

BACKGROUND

Abnormal central nervous system processing of visceral sensation may be a part of the pathogenesis behind idiopathic fecal incontinence (IFI). Our aim was to characterize brain differences in patients with IFI and healthy controls by means of structural magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI).

METHODS

In 21 female patients with IFI and 15 female healthy controls, whole-brain structural differences in gray matter volume (GMV), cortical thickness, and white matter tracts fractional anisotropy (FA) were quantified. For this purpose, we used voxel-based morphometry, surface based morphometry and tract-based spatial statistic, respectively. Furthermore, associations between structural brain characteristics and latencies of rectal sensory evoked electroencephalography potentials were determined.

KEY RESULTS

Compared to healthy controls, IFI patients had significantly reduced FA values, reflecting reduced white matter tract integrity, in the left hemisphere superior longitudinal fasciculus (SLF), posterior thalamic radiation, and middle frontal gyrus (MFG), all P<.05. No differences were observed in GMV or in cortical thickness. The reduced FA values in the SLF and MFG were correlated with prolonged latencies of cortical potentials evoked by rectal stimuli (all P<.05).

CONCLUSIONS & INFERENCES

This explorative study suggests that IFI patients have no macrostructural brain changes, but exhibit microstructural changes in white matter tracts relevant for sensory processing. The clinical relevance of this finding is supported by its correlations with prolonged latencies of cortical potentials evoked by rectal stimulation. This supports the theories of central nervous system changes as part of the pathogenesis in IFI patients.

Stromal Cell-Derived Factor 1 Plasmid Regenerates Both Smooth and Skeletal Muscle After Anal Sphincter Injury in the Long Term

BACKGROUND

Regenerating muscle at a time remote from injury requires re-expression of cytokines to attract stem cells to start and sustain the process of repair.

OBJECTIVE

We aimed to evaluate the sustainability of muscle regeneration after treatment with a nonviral plasmid expressing stromal cell-derived factor 1.

DESIGN

This was a randomized study.

SETTINGS

The study was conducted with animals in a single research facility.

INTERVENTIONS

Fifty-six female age-/weight-matched Sprague-Dawley rats underwent excision of the ventral half of the anal sphincter complex. Three weeks later, rats were randomly allocated (n = 8) to one of the following groups: no treatment, 100 μg of plasmid encoding stromal cell-derived factor 1 injected locally, local injection of plasmid and 8 × 10 bone marrow-derived mesenchymal stem cells, and plasmid encoding stromal cell-derived factor 1 injected locally with injection of a gelatin scaffold mixed with bone marrow-derived mesenchymal stem cells.

MAIN OUTCOME MEASURES

Anal manometry, histology, immunohistochemistrym and morphometry were performed 8 weeks after treatment. Protein expression of cytokines CXCR4 and Myf5 was investigated 1 week after treatment (n = 6 per group). ANOVA was used, with p < 0.0083 indicating significant differences for anal manometry and p < 0.05 for all other statistical analysis.

RESULTS

Eight weeks after treatment, all of the groups receiving the plasmid had significantly higher anal pressures than controls and more organized muscle architecture in the region of the defect. Animals receiving plasmid alone had significantly greater muscle in the defect (p = 0.03) than either animals with injury alone (p = 0.02) or those receiving the plasmid, cells, and scaffold (p = 0.03). Both smooth and skeletal muscles were regenerated significantly more after plasmid treatment. There were no significant differences in the protein levels of CXCR4 or Myf5.

LIMITATIONS

The study was limited by its small sample size and because stromal cell-derived factor 1 was not blocked.

CONCLUSIONS

A plasmid expressing stromal cell-derived factor 1 may be sufficient to repair an injured anal sphincter even long after the injury and in the absence of mesenchymal stem cell or scaffold treatments. See Video Abstract at http://links.lww.com/DCR/A451.

Brain responses to mechanical rectal stimulation in patients with faecal incontinence: an fMRI study

AIM

Continence is dependent on anorectal-brain interactions. Consequently, aberrations of the brain-gut axis may be important in the pathophysiology of faecal incontinence (FI) in certain patients. The aim of this study was to assess the feasibility of recording brain responses to rectal mechanical stimulation in patients with FI using functional magnetic resonance imaging (fMRI).

METHOD

A prospective, cohort pilot study was performed to assess brain responses during rectal stimulation in 14 patients [four men, mean (SD) age 62 (15) years]. Blood oxygen level dependent (BOLD) signals were measured by fMRI during rest and mechanical distension, involving random repetitions of isobaric phasic rectal distensions at fixed (15 and 45 mmHg) and variable (10% above sensory perception threshold) pressures.

RESULTS

Increases in BOLD signals in response to high pressure rectal distension (45 mmHg) and maximum toleration were observed in the cingulate gyrus, thalamus, insular cortex, inferior frontal gyrus, cerebellum, caudate nucleus, supramarginal gyrus, putamen and amygdala. Additionally, activation of the supplementary motor cortex and caudate nucleus with inconsistent activity in the frontal lobe was observed.

CONCLUSIONS

This study has demonstrated the feasibility of recording brain responses to rectal mechanical stimulation using fMRI in patients with FI, revealing activity in widespread areas of the brain involved in visceral sensory processing. The observed activity in the supplementary motor cortex and caudate nucleus, with relative paucity of activity in the frontal lobes, warrants investigation in future studies to determine whether aberrations in cerebral processing of rectal stimuli play a role in the pathogenesis of FI.

Genetic Influences of OPRM1, OPRD1 and COMT on Morphine Analgesia in a Multi-Modal, Multi-Tissue Human Experimental Pain Model

Human studies on experimentally induced pain are of value to elucidate the genetic influence on morphine analgesia under controlled conditions. The aim of this study was to investigate whether genetic variants of mu-, kappa- and delta-opioid receptor genes (OPRM1, OPRK1 and OPRD1) and catechol-O-methyltransferase gene (COMT) are associated with the morphine analgesia. The study was a randomized, double-blind, two-way, crossover, single-dose study conducted in 40 healthy participants, where morphine was compared with placebo. Pain was induced by contact heat, muscle pressure, bone pressure, rectal stimulations (mechanical, electrical and thermal) and cold pressor test (immersion of the hand into ice water). Sixteen genetic polymorphisms of four candidate genes were explored. Variability in morphine analgesia to contact heat stimulation was associated with COMT rs4680 (p = 0.04), and rectal thermal stimulation was associated with OPRM1 rs9479757 (p = 0.03). Moreover, in males, variability in morphine analgesia to rectal thermal stimulation was associated with OPRD1 polymorphisms: rs2234918 (p = 0.01) and rs533123 (p = 0.046). The study was explorative and hypothesis-generating due to the relatively small study size. However, results suggest that genetic variants in the COMT and OPRM1 irrespective of gender, and OPRD1 in males may contribute to the variability in morphine analgesia in experimental pain models.

Does Sacral Nerve Stimulation Improve Continence Through Enhanced Sensitivity of the Anal Canal? A Pilot Study

BACKGROUND

It has been suggested that the effects of sacral nerve stimulation against fecal incontinence involve neuromodulation at spinal or supraspinal levels.

OBJECTIVE

This study aims to investigate the afferent sensory pathways from the anorectum before and during sacral nerve stimulation.

DESIGN

This is an explorative study.

PATIENTS

Fifteen women with idiopathic fecal incontinence (mean age, 58 ± 12.2 years) were selected.

INTERVENTIONS

Cortical evoked potentials were recorded during repeated rapid balloon distension of the rectum and the anal canal both before and during temporary sacral nerve stimulation. Stimuli applied were individualized according to the subjective urge to defecate.

MAIN OUTCOME MEASURES

The main outcomes measured were 1) stimulus intensity, 2) latencies and amplitudes of cortical evoked potentials, and 3) spectral content in predefined frequency bands of cortical evoked potentials.

RESULTS

The median Wexner fecal incontinence score improved from 15.5 ± 3.6 before to 6.7 ± 5 during sacral nerve stimulation (p < 0.001). Sacral nerve stimulation did not affect the threshold for urge to defecate during rectal distension (p = 0.64) but reduced the threshold from stimulation of the anal canal by 50% (p = 0.03). No statistically significant differences were found in latencies, amplitudes, or spectral analysis.

LIMITATIONS

This is a pilot study of limited size.

CONCLUSIONS

In patients with idiopathic fecal incontinence, sacral nerve stimulation reduced the threshold for urge to defecate elicited from the anal canal, whereas supraspinal responses remained unaltered. This may suggest that sacral nerve stimulation, at least in part, acts via somatic afferent fibers enhancing anal sensation.