The factor structure and clinical utility of formal thought disorder in first episode psychosis

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Abstract

Background

Formal thought disorder (FTD) is a core feature of psychosis, however there are gaps in our knowledge about its prevalence and factor structure. We had two aims: first, to establish the factor structure of FTD; second, to explore the clinical utility of dimensions of FTD in order to further the understanding of its nosology.

Methods

A cross-validation study was undertaken to establish the factor structure of FTD in first episode psychosis (FEP). The relative utility of FTD categories vs. dimensions across diagnostic categories was investigated.

Results

The prevalence of clinically significant FTD in this FEP sample was 21%, although 41% showed evidence of disorganised speech, 20% displayed verbosity and 24% displayed impoverished speech. A 3-factor model was identified as the best fit for FTD, with disorganisation, poverty and verbosity dimensions (GFI = 0.99, RMR = 0.07). These dimensions of FTD accurately distinguished affective from non-affective diagnostic categories. A categorical approach to FTD assessment was useful in identifying markers of clinical acuteness, as identified by short duration of untreated psychosis (OR = 2.94, P < 0.01) and inpatient treatment status (OR = 3.98, P < 0.01).

Conclusion

FTD is moderately prevalent and multi-dimensional in FEP. Employing both a dimensional and categorical assessment of FTD gives valuable clinical information, however there may be a need to revise our conceptualisation of the nosology of FTD. The prognostic value of FTD, as well as its neural basis, requires elucidation.

Introduction

Language dysfunction plays a central role in the clinical presentation of psychosis. Crow postulated that schizophrenia is the price that man has paid for the development of language and, since Bleuler, loosening of associations has been recognised as a core feature of psychosis (Crow, 1997, Bleuler, 1958). Language disturbances may represent a psychosis endophenotype and disorganised speech may be considered to exist on a continuum (Raballo and Parnas, 2011, Remberk et al., 2012, Roche et al., 2015). Reported estimates of FTD prevalence in mental illness vary widely, depending on clinical assessment tool utilised and the population studied (Pearlson et al., 1989, Marengo and Harrow, 1987). Although there are many possible levels of language disturbance in psychosis only FTD is included in the major diagnostic classification systems (First et al., 2002, World Health Organization, 1992). FTD is not a unitary construct, however, and up to six different domains are identified on factor analysis (Cuesta and Peralta, 1999).

Andreasen described a bipolar “negative” versus “positive” factor structure to FTD and, to a certain degree, these FTD subtypes have distinct clinical and neuro-anatomical correlates (Andreasen, 1979). Negative FTD is quite predictive of poor functional outcome (Andreasen and Grove, 1986, Wilcox et al., 2014), and has been associated with reductions in medial frontal/orbitofrontal cortical grey matter (Sans-Sansa et al., 2013). Conversely, positive FTD may be an indicator or greater symptomatic severity (Roche et al., 2015, Jampala et al., 1989), and may be associated with volume reductions in Wernicke's and Broca's areas (Sans-Sansa et al., 2013). Verbiage disturbance and disorganised speech correctly identify up to 91% of schizophrenia versus mania diagnoses, however a two-factor structure does not adequately reflect the full clinical complexity of FTD (Taylor et al., 1994). Other dimensions, such as “idiosyncratic” and “attentional”, have more recently been identified and demonstrate some diagnostic validity (Cuesta and Peralta, 1999, Cuesta and Peralta, 2011a).

Authors of the Diagnostic and Statistical Manual, 5th Edition (DSM-V) emphasise the importance of dimensional assessment of psychopathology (Heckers et al., 2013). The limitations of a categorical approach to diagnosis are well recognised: diagnostic groups have significant overlap in their clinical presentation, management strategies, prognosis, genetic underpinnings and clinical course (Kamphuis and Noordhof, 2009, Owen et al., 2007, Whitty et al., 2005, Bromet et al., 2011, Van et al., 2009). To date most FTD research has investigated only those diagnosed with schizophrenia, often drawing from hospital and institutional samples (Taylor et al., 1994, Berenbaum et al., 1985, Mortimer et al., 1990). Although there has been a move towards investigating FTD in mixed diagnostic samples, the clinical utility of FTD dimensions has received little investigation (Cuesta and Peralta, 2011a). Furthermore, to date there has been no study of FTD in FEP. This is important because this population has had limited exposure to neuroleptics, the long-term effects of which can influence language function (Spohn et al., 1986, Goldberg et al., 2000).

To investigate the prevalence and factor structure of FTD in a mixed diagnostic FEP sample. To compare the clinical utility and diagnostic validity of dimensional vs. categorical assessment of FTD.

  • 1.

    To perform a cross-validation study of the factor structure of FTD, as assessed by the Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of Negative Symptoms (SANS), in a randomly-divided FEP sample (Andreasen, 1984a, Andreasen, 1984b).

  • 2.

    To establish the prevalence of FTD in a FEP sample.

  • 3.

    To establish whether dimensional FTD identified through factor analysis contributes to diagnostic validity and clinical utility in excess of categorical FTD assessment. A clinical characteristic possesses utility if it “provides nontrivial information about prognosis and likely treatment outcomes, and/or testable propositions about biological and social correlates” (Kendell and Jablensky, 2003).

Section snippets

Participant selection

We included individuals aged 16–65 years old who were diagnosed with affective and non-affective FEP by an early intervention in psychosis (EIP) service between February 2006 and July 2014. Participants were referred to the EIP service from general practitioners, outpatient departments and inpatient units in three defined mental health catchment areas in the Dublin Mid-Leinster region of Ireland. This includes a total catchment of 390,000 individuals, and includes referrals from a private

General characteristics

625 individuals were diagnosed with FEP from February 2005–July 2014. Excluding those with missing SAPS or SANS data (n = 6) and those diagnosed with psychosis due to a general medical condition (n = 16), the sample used for analysis was 603. The mean age at presentation was 34 years (s.d. 12) and the median was 31 years. 56% (n = 340) of the sample was male. Clinical and demographic characteristics of the sample are described in Table 1.

Sub-sample 1: EFA group

Bartlett's test of sphericity had a significance level of P < 

Prevalence of FTD

Reported FTD prevalence ranges from 6 to 81% (Pearlson et al., 1989, Marengo and Harrow, 1987). Our figure of 21%, similar to that reported by Howard et al (27.4%), reflects prevalence of FTD of sufficient severity to “substantially impair effective communication” (Howard et al., 1993). Precise estimation of the burden of FTD is important, not only to inform our knowledge of the epidemiology of psychotic illness, but also because those with higher burdens of disorganised symptoms may respond

Conflict of interest

None of the authors have any conflict of interest to declare.

Contributors

Eric Roche and Mary Clarke wrote the study protocol. Eric Roche, John Lyne, Brian O'Donoghue, Mary Clarke, Brendan Kelly, Kevin Malone and Ailish Hannigan designed the study. Eric Roche, John Lyne, Mary Clarke, Ricardo Segurado and Anthony Kinsella carried out statistical analyses. Eric Roche wrote the first draft of the manuscript and all co-authors contributed to and approved the final draft.

Funding

This project was funded in part by a grant administered to the corresponding author from the Health Research Board of Ireland, grant number HPF-2013-468.

Acknowledgements

The authors would like to acknowledge the participating patients and families, as well as the clinical directors of the mental health services involved, who facilitated this study. The authors also express their gratitude to the librarians in St John of God Hospital – Daria Brennan, Carla Senf and Angela Kearney – for their support throughout this study.

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