title: The Epidemiology and Associated Phenomenology of Formal Thought Disorder: A Systematic Review.
abstract: BACKGROUND
  Authors of the Diagnostic and Statistical Manual, Fifth Edition (DSM-V) have recommended to "integrate dimensions into clinical practice." The epidemiology and associated phenomenology of formal thought disorder (FTD) have been described but not reviewed. We aimed to carry out a systematic review of FTD to this end.
  
  
  METHODS
  A systematic review of FTD literature, from 1978 to 2013, using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.
  
  
  RESULTS
  A total of 881 abstracts were reviewed and 120 articles met inclusion criteria; articles describing FTD factor structure (n = 15), prevalence and longitudinal course (n = 41), role in diagnosis (n = 22), associated clinical variables (n = 56), and influence on outcome (n = 35) were included. Prevalence estimates for FTD in psychosis range from 5% to 91%. Dividing FTD into domains, by factor analysis, can accurately identify 91% of psychotic diagnoses. FTD is associated with increased clinical severity. Poorer outcomes are predicted by negative thought disorder, more so than the typical construct of "disorganized speech."
  
  
  CONCLUSIONS
  FTD is a common symptom of psychosis and may be considered a marker of illness severity. Detailed dimensional assessment of FTD can clarify diagnosis and may help predict prognosis.
authors.affiliation: DETECT Early Intervention in Psychosis Service, Dublin, Ireland; eric.roche@sjog.ie.
authors.forename: Eric
authors.initials: E
authors.lastname: Roche
authors.affiliation: Cluain Mhuire Community Mental Health Service, Dublin, Ireland;
authors.forename: Lisa
authors.initials: L
authors.lastname: Creed
authors.affiliation: University College Dublin, Dublin, Ireland;
authors.forename: Donagh
authors.initials: D
authors.lastname: MacMahon
authors.affiliation: St John of God Hospital, Dublin, Ireland.
authors.forename: Daria
authors.initials: D
authors.lastname: Brennan
authors.affiliation: DETECT Early Intervention in Psychosis Service, Dublin, Ireland;
authors.forename: Mary
authors.initials: M
authors.lastname: Clarke
mesh_terms: D003072:Cognition Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D011618:Psychotic Disorders / Q000150:complications / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology*; D013850:Thinking / Q000502:physiology*
keywords: communication; epidemiology; formal thought disorder; language; phenomenology; prognosis; psychosis; schizophrenia; thought disorder