title: Systematic review of the comorbidity of irritable bowel syndrome with other disorders: what are the causes and implications?
abstract: OBJECTIVE
  Comorbid or extraintestinal symptoms occur frequently with irritable bowel syndrome and account for up to three fourths of excess health care visits. This challenges the assumption that irritable bowel is a distinct disorder. The aims of this study were to (1) assess comorbidity in 3 areas: gastrointestinal disorders, psychiatric disorders, and nongastrointestinal somatic disorders; and (2) evaluate explanatory hypotheses.
  
  
  METHODS
  The scientific literature since 1966 in all languages cited in Medline was systematically reviewed.
  
  
  RESULTS
  Comorbidity with other functional gastrointestinal disorders is high and may be caused by shared pathophysiological mechanisms such as visceral hypersensitivity. Psychiatric disorders, especially major depression, anxiety, and somatoform disorders, occur in up to 94%. The nongastrointestinal nonpsychiatric disorders with the best-documented association are fibromyalgia (median of 49% have IBS), chronic fatigue syndrome (51%), temporomandibular joint disorder (64%), and chronic pelvic pain (50%).
  
  
  CONCLUSIONS
  Multivariate statistical analyses suggest that these are distinct disorders and not manifestations of a common somatization disorder, but their strong comorbidity suggests a common feature important to their expression, which is most likely psychological. Some models explain the comorbidity of irritable bowel with other disorders by suggesting that each disorder is the manifestation of varying combinations of interacting physiological and psychological factors. An alternative hypothesis is that the irritable bowel diagnosis is applied to a heterogeneous group of patients, some of whom have a predominantly psychological etiology, whereas others have a predominantly biological etiology, and that the presence of multiple comorbid disorders is a marker for psychological influences on etiology.
authors.affiliation: Division of Digestive Diseases and Center for Functional Gastrointestinal and Motility Disorders, University of North Carolina, Chapel Hill, North Carolina 27599, USA. Whitehd@unch.unc.edu
authors.forename: William E
authors.initials: WE
authors.lastname: Whitehead
authors.forename: Olafur
authors.initials: O
authors.lastname: Palsson
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Jones
mesh_terms: D003109:Colonic Diseases, Functional / Q000453:epidemiology*; D015897:Comorbidity; D005767:Gastrointestinal Diseases / Q000453:epidemiology; D006801:Humans; D001523:Mental Disorders / Q000453:epidemiology; D011602:Psychophysiologic Disorders / Q000453:epidemiology