Decreased cortical activation during rectal distention in patients with functional constipation with normal rectal compliance

Abstract

Background: Patients with chronic constipation have loss of or diminished urge sensation. The underlying cortical processing for the alteration of urge sensation is unknown. We postulated there might be abnormal or diminished cortical processing in patients with constipation. Aim: to investigate cortical processing in patients with functional constipation. Methods: Patients with functional constipation (n=19) and normal healthy subjects (n=13) were recruited. The rectal compliance in both group was determined using barostat. The mean urge sensation of the normal subjects were calculated and then the subliminal, liminal and supraliminal pressures were determined. Patients were required to press a button indicating urge or strong sensation. Functional MRI based on the Oxygenation Level Dependent (BOLD) effect carried out in a 3T MRI System was performed for both groups with the barostat connected. The distention paradigm consisted of subliminal, liminal and supraliminal pressures interleaved with rest period. The software SPM99 was used for data analysis. Results: There was no difference in sex (p=0.6), age (p=0.15) or rectal compliace (6.6 ± 3.7 vs 6.0 ± 1.6 ml/mmHg, p=0.064) in the constipated and control groups. The mean urge sensation of the healthy subjects was 30mmHg, therefore the subliminal, liminal, and supraliminal pressures were 15mmHg, 30mmHg, and 45mmHg, respectively. The cortical areas represented at subliminal and supraliminal pressures were similar in both groups. However, the volume of cortical activity at parietal lobe and precuneus was lower in constipated subjects at liminal pressure (P<0.003). There was frontal and limbic lobe activation in the normal subjects at urge sensation but not in constipated subjects (p<0.0034). Conclusion: Patient with functional constipation have impaired afferent pathway leading to abnormal urge sensation.