The Continuum Theory

Question 1

What is the concept of continuum in medicine?

Answer 1

• Most common illness cannot be entirely dichotomous in nature
• Aetiology is multifactorial, such as in psychiatric disorders

Question 2

Which type of disorders can arguably be considered as dichotomous entities, that is either present or absent?

Answer 2

Disorders caused by one gene = 100% penetrant

• very rare conditions

Question 3

How is the concept of continuum characterised in psychosis?

Answer 3

Phenotype can be expressed at levels below its clinical manifestation

-> psychosis proneness, psychotic experiences, schizotypy, at-risk mental states

Experiencing isolated symptoms (e.g. delusions, hallucinations, not necessarily associated with development of psychotic disorder)

-> presence of symptoms is not presence of disorder

Question 4

What is the epidemiological point of view on the continuum in psychosis?

Answer 4

Even though prevalence of clinical disorder is low, prevalence of symptoms can conceivably be much higher

Question 5

What is the schizotaxia proposed by Paul Meehl (1962)?

Answer 5

Genetic predisposition to schizophrenia

• individual would develop schizotypy or schizophrenia depending on environmental circumstances

Question 6

What were the limitations of the schizotaxia proposed by Paul Meehl (1962)?

Answer 6

• Favoured single major gene theory of schizophrenia (since proven false by genetic linkage studies)
• He viewed schizotypy as the only clinical phenotype of schizotaxia

Question 7

How has Paul Meehl’s schizotaxia (1962) been used?

Answer 7

• Did not enter diagnostic nomenclatures, but used in research to indicate the premorbid neurological substrate of schizophrenia
• In 2000s: research suggests schizotaxia may be a clinically consequential condition

Question 8

What does Meehl’s original quasi-dimensional model provide today?

Answer 8

Fully dimensional model of psychosis continuum

• framework of description of inter-individual heterogeneity and variation of phenotypic expression
• integrates most of the elements of quasi-dimensional model
• includes transitory anomalous experiences in the general non-clinical population

Question 9

What did the study of van Os and colleagues (2000) on the psychosis continuum in the general population show?

Answer 9

Presence of psychotic experiences in both clinical and non-clinical populations

• psychotic symptoms in clinical sample show to be “points on continua function”
• surveys showed large numbers of individuals report experiences resembling symptoms of psychotic patients

Question 10

What did the systematic review and meta-analysis of the psychosis continuum by van Os and colleagues (2009) suggest?

Answer 10

Psychosis phenotype may be nearly 5 times more prevalent than psychotic disorder

• 35 cohorts: 70-90% transitory psychotic experiences that disappear over time
• significant variation in prevalence and persistence of psychotic-like experiences
• 8% psychotic experiences ; 4% psychotic symptoms ; 3% psychotic disorder
• heterogeneity could be explained by difference in study population, methodology and definition of psychotic-like experiences

Question 11

What did the systematic review of Lee and colleagues (2009) show on measuring psychotic-like experiences?

Answer 11

• There’s a lot of heterogeneity between self-administered, structured and semi-structured instruments
• Naive assumption: psychotic-like experience can be measured independent from context being employed

Question 12

What does a phenomenological continuity of psychotic-like experiences (PLEs) suggest?

Answer 12

If there’s a continuum, than dynamic transitions over time, from subclinical non-prodromal manifestations to full-scale disorder, MUST occur over short and long periods of time

Question 13

What constitutes the predictive validity of psychotic-like experiences (PLEs)?

Answer 13

1. Environmental risk factors
   - transitory developmental expression of psychosis may become abnormally persistent and clinically relevant depending on degree of environmental risk the person is exposed to (sensitisation)
2. Genetic background factors
   - developmental psychotic experiences are common and mostly transitory (not permanent): 75-90%

Question 14

What is the clinical significance of psychotic-like experiences (PLEs) according to the systematic review and meta-analysis of Kaymaz and colleagues (2012)?

Answer 14

Risk of conversion to clinical psychotic outcome higher for individuals with PLEs than for those without

• 0.56% for exposed individual (with PLEs)
• 0.16% for individuals without PLEs

-> However, low transition risk

Question 15

What are the main arguments to support the continuum theory of psychosis?

Answer 15

• Psychotic symptoms are continuously distributed in general populations
• > therefore on a continuum
• Continua are more valid and easier to dissect biologically and would lead to faster scientific and clinical progress

Question 16

What competes with the idea off psychosis as a continuum?

Answer 16

Categories of psychosis (categorical definitions) in diagnostic manuals (DSM-5, ICD-10)

Question 17

What did Stephen Lawrie criticised about the continuum theory of psychosis?

Answer 17

• Scientifically unproven

- Clinically impractical

Question 18

What were Stephen Lawrie’s four point of criticism on the continuum theory of psychosis?

Answer 18

1. Just because psychotic symptoms are continuously distributed in general population, does not mean schizophrenia and other psychoses are qualitatively indistinct from normal experiences
2. No guarantee that a psychosis continuum is more valid and will aid scientific progress, individual symptoms are less likely reliably identified than multidimensional diagnosis, they vary in severity over time and may differ in different environmental contexts
3. Continuous measures are routinely employed in the rest of medicine (e.g. blood pressure) when they can be simply and reliably assessed in one dimension
   - no simple or easily used measurement: prevalence of psychotic experiences differs according to instrument used
4. Established diagnostic categories for psychosis are clinically useful (regulate and prescribe treatments based on currently available replicated clinical trial evidence)
   - need to make dichotomous decision such whether or not to legally detain people
   - categories more easily used and communicated than continua

-> more research needed

Question 19

What are the advantages of categories?

Answer 19

• Ease of use: description, communication, conceptualisation

- Familiarity: typologies used in the rest of medicine and biology

Question 20

What are the disadvantages of categories?

Answer 20

• Can distort perceptions of individuals, whether ill or well
• Convey limited (stereotyped) information

Question 21

What are the advantages of continua?

Answer 21

• Flexible measurement

- Many biological variables are dimensional (e.g. age)

Question 22

What are the disadvantages of continua?

Answer 22

• Need to be simple (uni-axial) to be practicable (e.g. blood pressure)
• Many biological variables are categories (e.g. gender)

Question 23

What is the problem of phenomenological continuity in psychosis?

Answer 23

Epidemiological error:

• Subthreshold psychotic symptoms (e.g. PLEs) are not a product or original research into real-life world of psychosis, BUT a reflection-based attenuation of DSM criteria for schizophrenia
• Notions of “psychotic experiences” and “psychotic symptoms” are used without explanation of what makes a symptoms psychotic
• Since DSM-III, the “symptom” is considered an object existing in itself, in the absence of holistic and contextual considerations

Question 24

What are the consequences of the epistemological error of phenomenological continuity?

Answer 24

• Homogenisation, trivialisation, and non-specificity of mental symptoms
• > Illusion of phenomenological continuity

Question 25

What does empirical evidence indicate on the importance of context in attenuated psychotic symptoms (Fusar-Poli et al., 2016)?

Answer 25

Developmental and experiential context impacts the clinical significance of attenuated psychotic symptoms

Question 26

How can attenuated psychotic symptoms be measured?

Answer 26

• CAARMS (Comprehensive Assessment of At Risk Mental State): semi-structured interviews requiring raters to undergo specific psychopathological training (2-hours to administer)
• CAPE: widely used to measure PLEs, self-administered (few minutes)

Question 27

Does it make any difference to elicit psychotic-like experiences via CAARMS or CAPE (Schiltze-Lutter et al., 2013)?

Answer 27

Yes:
CAARMS and CAPE share qualitative item similarities but also important differences

• clinical significance of responses to the questions cannot be “predefined” by virtue of similar verbal formulation
• attenuated psychotic symptoms (e.g. PLEs) are not independent of their developmental and experiential context
• articulation of a symptom is not entirely independent of the way in which it is elicited (self-assessment in CAPE vs. semi-structured interview by psychiatrist in CAARMS)

Question 28

What is the view of Josef Parnas on the assessment of attenuated psychotic symptoms (Parnas and Henriksen, 2016)?

Answer 28

Early diagnostic assessment requires: symptomatic screening, considerable psychopathological knowledge, insight into patient’s like

-> it’s unjustifiable to perceive a symptom in abstraction from other symptoms, larger contexts, and structures of consciousness

Question 29

What is the current validity and utility of the continuum model of psychosis?

Answer 29

• Limited empirical research support
• Questionable clinical utility
• No clear advantages compared to categorical model