Does Psychosis Exist on a Continuum?

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• What is psychosis?
• Dimensional versus categorical classification of mental health disorders
• The continuum of psychosis

What is psychosis?

Psychosis is an umbrella term which refers to a group of symptoms that affect the mind, involving some loss of contact with reality. Typically, psychotic symptoms include hallucinations which includes seeing, hearing or smelling things that do not exist, and delusions which are strongly held false beliefs, usually rooted in fear, suspicion or grandiosity.

Other symptoms can include bizarre behavior and disorganized speech. These symptoms are referred to as positive symptoms. People with psychosis can also display negative symptoms, which include flattening of affect, loss of motivation and social withdrawal. Positive and negative symptoms often co-occur with cognitive disruptions such as disordered thoughts or difficulties in concentration.

Although psychosis can have multiple causes such as drug use, brain injury, extreme stress or sleep deprivation, it is most commonly caused by mental illness such as schizophrenia or bipolar disorder. People with these diagnoses can have extended periods of time without these symptoms, usually when medication is effective. When they re-occur, the person is said to be experiencing a psychotic episode.

Dimensional versus categorical classification of mental health disorders

Traditional models have adopted a categorical model of disorders and diagnoses. Application of this model means an individual either has a disorder, or they do not. To be identified as having a disorder, an individual must meet a specific set of criteria. For example, according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition for an individual to be diagnosed as having schizophrenia, they must display two or more of the following:

• Delusions,
• Hallucinations,
• Disorganized speech,
• Grossly disordered or catatonic behavior,
• Negative symptoms such as loss of motivation, poverty of speech or affective flattening.

Such symptoms must have present for at least one month (less if they respond positively to antipsychotic medication) and be sufficiently intense to cause impairment.

Conversely, the dimensional approach assesses psychosis along a spectrum ranging from mild to severe with respect to impairment. These differences in degree have implications for treatment.

Current diagnostic systems in psychiatry such as DSM-5 and the international statistical classification of diseases and related health problems use the categorical approach. Symptoms are observed and used to assign individuals to distinct non-overlapping categories. This approach allows for the validity and utility of such criteria to be empirically tested and has increased reliability in psychiatric diagnosis. However, the categorical approach is unable to reflect the complex etiology of mental illness, limiting its validity. However, the DSM-5 does have a categorization for Psychotic Disorder not otherwise specified, that may be used by clinicians to identify patients that seem to exhibit many traits of psychosis but may not meet the full criteria for a specific psychotic disorder such as schizophrenia.

The continuum of psychosis

Increasingly, the dimensional approach is being applied to psychosis. This is referred to as the continuum of psychosis and assumes that psychotic symptoms exist on a continuum across the general population. Support for this approach comes from studies of the general population, clinical populations and co-morbidity in psychosis.

Studies of the general population

Psychotic-like symptoms are common, especially among young people. They have an estimated lifetime prevalence of approximately 7% in adults with 2.5% of the general population having reported psychotic experiences within the past year. In studies of young people, rates of psychotic-like symptoms are exponentially higher, with lifetime prevalence rates of up to 66% in one study. Moreover, such symptoms are age dependent and reach a peak in adolescence, suggesting that such experiences may be characteristic of normal neurodevelopmental processes.

Psychotic-like symptoms as predictors of psychotic disorder

A categorical model of psychosis would suggest that the presence of psychotic-like symptoms would be a strong predictor of future psychotic disorder. However, population studies have shown that whilst the prevalence of psychotic symptoms is high, rates of psychotic disorder are much lower, around 26.6 per 100,000 person-years.

When longitudinal studies include people at high risk of developing psychosis (those showing subclinical psychotic symptoms accompanied by brief limited intermittent psychotic symptoms and significant decline in functioning), only one-third will ultimately meet criteria to be diagnosed with a psychotic disorder. When research is conducted in primary mental health care settings transition rates are much lower, with only 10% of people reporting psychotic-like symptoms developing a psychotic disorder.

Co-morbidity in psychosis

Psychotic symptoms are observable in numerous psychiatric disorders, including Alzheimer’s Disease, depression, anxiety and obsessive-compulsive disorder, and usually predict poorer prognosis, treatment response and global functioning. In these disorders, psychotic symptoms may be markers of complexity rather than indicators of future psychotic disorder. Categorical models of psychosis are unable to account for this complex interplay of symptoms and disorder progression.

References

• Addington J, Cornblatt BA, Cadenhead KS, Cannon TD, McGlashan TH, Perkins DO, Seidman LJ, Tsuang MT, Walker EF, Woods SW, Heinssen R. At clinical high risk for psychosis: outcome for nonconverters. Am J Psychiatry. 2011 Aug;168(8):800-5. doi: 10.1176/appi.ajp.2011.10081191. Epub 2011 Apr 15. https://www.ncbi.nlm.nih.gov/pubmed/21498462
• American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA: American Psychiatric Association, 2013.
• Calkins ME, Moore TM, Merikangas KR, Burstein M, Satterthwaite TD, Bilker WB, Gur RE. The psychosis spectrum in a young US community sample: findings from the Philadelphia Neurodevelopmental Cohort. World Psychiatry. 2014;13(3):296–305. https://www.ncbi.nlm.nih.gov/pubmed/25273303
• Claridge G. The schizophrenias as nervous types. The British Journal of Psychiatry. 1972;121(560):1–17. https://www.ncbi.nlm.nih.gov/pubmed/5047166
• Fusar-Poli P, Van Os. Lost in transition: setting the psychosis threshold in prodromal research. Acta Psychiatr Scand. 2013 Mar;127(3):248-52. doi: 10.1111/acps.12028. Epub 2012 Nov 9. https://www.ncbi.nlm.nih.gov/pubmed/23136851
• Jongsma HE, Turner C, Kirkbride JB, Jones PB. International incidence of psychotic disorders, 2002-17: a systematic review and meta-analysis. Lancet Public Health. 2019 May;4(5):e229-e244. doi: 10.1016/S2468-2667(19)30056-8. https://www.ncbi.nlm.nih.gov/pubmed/31054641
• Laurens KR, Hobbs MJ, Sunderland M, Green MJ, Mould GL, Arango C, Deboutte D. Psychotic-like experiences in a community sample of 8000 children aged 9 to 11 years: an item response theory analysis. Psychological medicine. 2012;42(7):1495–1506. https://www.ncbi.nlm.nih.gov/pubmed/21999924
• Linscott RJ, Van Os J. An updated and conservative systematic review and meta-analysis of epidemiological evidence on psychotic experiences in children and adults: on the pathway from proneness to persistence to dimensional expression across mental disorders. Psychol Med. 2013;43(6):1133–1149. https://www.ncbi.nlm.nih.gov/pubmed/22850401
• Loch A. Schizophrenia, Not a Psychotic Disorder: Bleuler Revisited. Front. Psychiatry, 10 May 2019  https://doi.org/10.3389/fpsyt.2019.00328
• Nuevo R, Chatterji S, Verdes E, Naidoo N, Arango C, Ayuso-Mateos JL. The continuum of psychotic symptoms in the general population: a cross-national study. Schizophr Bull. 2012;38(3):475–485. https://www.ncbi.nlm.nih.gov/pubmed/20841326
• Perez J, Russo DA, Stochl J, Clarke J, Martin Z, Jassi C, French P, Fowler 7, Jones PB. Common mental disorder including psychotic experiences: Trailblazing a new recovery pathway within the Improving Access to Psychological Therapies programme in England. Early Interv Psychiatry. 2018 Jun;12(3):497-504. doi: 10.1111/eip.12434. Epub 2017 May 16. https://onlinelibrary.wiley.com/doi/abs/10.1111/eip.12434
• Potuzak M, Ravichandran, C Lewandowski KE, Ongür D, Cohen BM. Categorical vs dimensional classifications of psychotic disorders. Compr Psychiatry. 2012 Nov; 53(8): 1118–1129. Published online 2012 Jun 7. doi: 10.1016/j.comppsych.2012.04.010m. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3488145/

Further Reading

• All Psychosis Content
• Psychosis – What is Psychosis?
• What Causes Psychosis?
• Psychosis Pathophysiology
• Cannabis and Psychosis

Written by

Clare Knight

Since graduating from the University of Cardiff, Wales with first-class honors in Applied Psychology (BSc) in 2004, Clare has gained more than 15 years of experience in conducting and disseminating social justice and applied healthcare research.