title: Phenotypic variation in functional disorders of defecation.
abstract: OBJECTIVE
  Although obstructed defecation is generally attributed to pelvic floor dyssynergia, clinical observations suggest a wider spectrum of anorectal disturbances. Our aim was to characterize phenotypic variability in constipated patients by anorectal assessments.
  
  
  METHODS
  Anal pressures, rectal balloon expulsion, rectal sensation, and pelvic floor structure (by endoanal magnetic resonance imaging) and motion (by dynamic magnetic resonance imaging) were assessed in 52 constipated women and 41 age-matched asymptomatic women. Phenotypes were characterized in patients by principal components analysis of these measurements.
  
  
  RESULTS
  Among patients, 16 had a hypertensive anal sphincter, 41 had an abnormal rectal balloon expulsion test, and 20 had abnormal rectal sensation. Forty-nine patients (94%) had abnormal pelvic floor motion during evacuation and/or squeeze. After correcting for age and body mass index, 3 principal components explained 71% of variance between patients. These factors were weighted most strongly by perineal descent during evacuation (factor 1), anorectal location at rest (factor 2), and anal resting pressure (factor 3). Factors 1 and 3 discriminated between controls and patients. Compared with patients with normal (n = 23) or reduced (n = 18) perineal descent, patients with increased (n = 11) descent were more likely (P < or = .01) to be obese, have an anal resting pressure >90 mm Hg, and have a normal rectal balloon expulsion test result.
  
  
  CONCLUSIONS
  These observations demonstrate that functional defecation disorders comprise a heterogeneous entity that can be subcharacterized by perineal descent during defecation, perineal location at rest, and anal resting pressure. Further studies are needed to ascertain if the phenotypes reflect differences in the natural history of these disorders.
authors.affiliation: Division of Gastroenterology and Hepatology, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA. bharucha.adil@mayo.edu
authors.forename: Adil E
authors.initials: AE
authors.lastname: Bharucha
authors.forename: Joel G
authors.initials: JG
authors.lastname: Fletcher
authors.forename: Barb
authors.initials: B
authors.lastname: Seide
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Riederer
authors.forename: Alan R
authors.initials: AR
authors.lastname: Zinsmeister
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000502:physiology; D002404:Catheterization; D003248:Constipation / Q000473:pathology* / Q000503:physiopathology*; D003672:Defecation; D005242:Fecal Incontinence / Q000473:pathology* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000592:standards / Q000706:statistics & numerical data; D008280:Magnetics; D008365:Manometry; D008875:Middle Aged; D015588:Observer Variation; D010502:Perineum / Q000502:physiology; D010641:Phenotype; D015203:Reproducibility of Results; D012677:Sensation