title: Pain and mechanical properties of the rectum in patients with active ulcerative colitis.
abstract: BACKGROUND
  The pain, urgency, and incontinence in ulcerative colitis may be related to changes in viscoelastic properties of the gut wall or to alterations of the sensory pathways. In the present study, we used an advanced rectal probe to study the mechanosensory and smooth muscle properties in patients with active disease.
  
  
  METHODS
  Nine patients with ulcerative colitis (mean age 39.5 years) with exacerbation limited to the rectum and sigmoid colon and 17 age-matched healthy subjects were included. The rectum was distended before and after pharmacological relaxation of the smooth muscle until moderate pain was reported, and the cross-sectional area, volume, pressure, tension, and strain were computed. To investigate central integration of a tonic stimulus, the bag was finally distended to the pain threshold; then, the cross-sectional area was held constant for 2 min.
  
  
  RESULTS
  The patients were hypersensitive to mechanical stimuli as assessed by the cross-sectional area (F = 21.7; P < 0.001). There were no differences in compliance or stiffness between the 2 groups, but the hypersensitivity was abolished after muscle relaxation. Together with the muscle analysis, this finding demonstrated that the smooth muscles were tonically contracted in the inflamed rectum, resulting in a decreased rectal circumference. The tonic distensions did not evoke central integration of the pain response, indicating that hyperalgesia is more likely related to peripheral factors.
  
  
  CONCLUSIONS
  Patients with active ulcerative colitis have hypersensitivity and increased tone of the smooth muscles, which may explain the symptoms. Drugs that affect smooth muscle contraction may be helpful in difficult cases.
authors.affiliation: Center for Visceral Biomechanics and Pain, Department of Gastroenterology, Aalborg University, Denmark. drewes@smi.auc.dk
authors.forename: Asbjørn Mohr
authors.initials: AM
authors.lastname: Drewes
authors.forename: Jens Brøndum
authors.initials: JB
authors.lastname: Frøkjaer
authors.forename: Ejnar
authors.initials: E
authors.lastname: Larsen
authors.forename: Hariprasad
authors.initials: H
authors.lastname: Reddy
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Hans
authors.initials: H
authors.lastname: Gregersen
mesh_terms: D000328:Adult; D003093:Colitis, Ulcerative / Q000150:complications / Q000503:physiopathology*; D018450:Disease Progression; D004548:Elasticity; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000503:physiopathology; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement; D010812:Physical Stimulation; D010865:Pilot Projects; D012007:Rectum / Q000503:physiopathology*; D012720:Severity of Illness Index