Psychosis as a continuum is based on the fact that the incidence of individuals displaying symptoms of psychosis is significantly higher in the general population than the numbers diagnosed with psychotic disorder. Thus, a proportion of the population experiencing psychotic episodes remain undiagnosed and often can maintain a normal lifestyle without the requirement for diagnosis and treatment.

Recent meta analyses of vast pools of test subjects showed that approximately 7% of the population experience psychotic episodes (van Os, J., et al. 2009). With only 3% experiencing these to a severity that qualifies for diagnosis of a psychotic disorder. This 3% lie on the extreme end of the continuum above the threshold to satisfy specific clinical diagnostic criteria.

The continuum theory is in conflict with the traditional stance in psychiatry that psychosis is a manifestation of a distinct disorder: Either the psychotic disorder is present or it is absent in an individual and therefore categorically absolute allowing for no overlap.

The continuum theory gained further traction with the planning of the latest editions of the DSM and ICD manuals, as its supporters called for the remodelling of diagnostic categories and criteria regarding psychosis based on a continuum model. This was met with fierce criticism from many who believed that the continuum theory had insufficient credibility and that introducing the continuum approach in its current format would be naïve, reckless and overlooking the longstanding benefits of the dichotomous model which has undergone decades of rigorous scientific research, development and effective application (Lawrie et al., 2010).

Psychosis is considered to be a disorder with multiple contributing biological and psychological factors which individually show a linear risk association. Therefore, by compounding these effects they should maintain a linear risk correlation which supports the continuum model and not diagnostic thresholds as in the dichotomous model (Jones et al. 1994). Furthermore, psychosis distribution can be illustrated as a continuous half-normal demographic curve further supporting the continuum model rather than the dichotomous one which would predict a curve bearing two population groups peaks with no overlap.

Van Os et al. (2001) carried out a study of 7076 people in 5 different locations of varying levels of urban density. It was predicted that following the continuum model, the mean psychosis rate of each population would predict the frequency of psychotic disorders. His evidence proved there was a direct correlation, thus proving the continuum theory to be valid.

The concept of Shizotypy adds support to the continuum model. It describes a continuum of personality with varying degrees of personality traits and experience which feature prominently in psychotic disorders. Creative types such as artists and poets were demonstrated to exhibit personality traits and unusual experience above controls and equal in many cases to those with schizophrenia (Nettle, D. 2006).

The introduction of Attenuated Psychosis Syndrome, which is accepted in the diagnostic manuals as a sub-threshold category for psychosis stands as evidence that a continuum is edging its way into the mainstream, as (APS) somewhat dissolves the dichotomy of psychosis (Reddy M. S., 2014).

A main critique of the continuum theory is that it inherently implies a lack of clear distinction between psychosis and normal experience as it rests on the observation that psychosis commonly pervades the general population, so can be considered in many cases to be on the spectrum of ‘normal’. In addition, it lacks clarity over whether a single continuum or multiple continua are required to cover the multifarious divergent forms of psychoses. Furthermore, there is insufficient flexibility in the continuum model to account for latent psychosis and complexities involved with distinguishing a multitude of psychosis subtypes (Lawrie et al., 2010). It instead has a relatively blanket approach to categorizing as its proponents have failed to outline criteria for diagnosis and intervention as comprehensively as the dichotomous approach, which is fundamental to the dominant DSM and ICD frameworks for psychosis.

The fact that a significant percentage of the general population experiences psychosis whilst not considered to have a disorder helps reduce stigmatization issues. Those diagnosed may also gain a modicum of relief and hope knowing that others manage to live relatively normal lives whilst sharing psychotic symptoms.

Meta-analyses of assessments show that symptoms in individuals displaying psychosis at sub-threshold levels for diagnosis are congruous with those in individuals expressing a psychotic disorder. Much in favour of the continuum model, as the dichotomous model does not predict for such phenomena. However, it is clear that extensive research, highly developed diagnostic criteria and subtyping will need to be in place for the continuum to take over as the dominant paradigm in psychiatry and psychology (Lawrie et al., 2010).

 

References:-

Stephen M. Lawrie, Jeremy Hall, Andrew M. McIntosh, David G. C. Owens and Eve C. Johnstone. The ‘Continuum of Psychosis’: Scientifically Unproven and Clinically Impractical. The British Journal of Psychiatry (2010) 197, 423–425.

Reddy M. S. (2014). Attenuated psychosis syndrome. Indian journal of psychological medicine, 36(1), 1–3.

van Os J, Linscott RJ, Myin-Germeys I, Delespaul P, Krabbendam L. (2009). A systematic review and meta-analysis of the psychosis continuum: evidence for a psychosis proneness-persistence-impairment model of psychotic disorder. Psychological Medicine 2009 Feb;39(2):179-95.

Jones P, Rodgers B, Murray R, Marmot M (1994). Child development risk factors for adult Schizophrenia in the British 1946 birth cohort. Lancet 344, 1398–1402.

Nettle, D. (2006). Schizotypy and Mental Health Amongst Poets, Visual Artist, and Mathematicians. Journal of Research in Personality Volume 40, Issue 6, December 2006, Pages 876-890

van Os J., Johns LC (2001). The continuity of psychotic experiences in the general population. Clinical Psychology

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