Schizophrenia

• Schizophrenia


  A mental disorder affecting 1% of the population, with onset typically around 15 to 45 years of age. Men are more likely to get it and have an earlier onset.
• Diagnostic and Statistical Manual (DSM)


  Most often used to diagnose schizophrenia
• International Classification of Disease (ICD)


  Can also be used to diagnose schizophrenia
• DSM-5


  Requires one positive symptom to diagnose schizophrenia
• ICD-10


  Requires two negative symptoms to diagnose schizophrenia
• Positive symptoms of schizophrenia


  • Hallucinations
  • Delusions
• Positive symptoms


  Additional experiences that are beyond those of ordinary existence
• Negative symptoms of schizophrenia

  • Avolition
  • Speech Poverty
• Negative symptoms


  Losses of normal experiences and abilities
• Reliability


  The extent to which a finding is consistent, such as different psychiatrists reaching the same diagnosis when independently assessing patients (inter-rater reliability)
• Test-retest reliability


  If the same thing measured under the same conditions yields the same results every time, i.e: the same doctor giving the same diagnosis over time for the same symptoms
• Inter-rater reliability of schizophrenia diagnosis is often low, with only a 54% concordance rate between doctors' assessments of 153 patients (Beck, 1963)
• However, Jakobsen et al. (2005) found a 98% concordance rate when using the ICD-10 classification system to diagnose schizophrenia in 100 Danish patients with a history of psychosis
• Validity


  The extent to which we are measuring what we are intending to measure, such as whether different assessment systems arrive at the same diagnosis for the same patient
• Comorbidity is when a person has more than one mental condition, and this is an issue for the validity of schizophrenia diagnosis as conditions like severe depression could be being misdiagnosed as schizophrenia
• Symptom overlap with other disorders like bipolar disorder is another issue for the validity of schizophrenia diagnosis
• Gender bias may also affect the validity of schizophrenia diagnosis, as men may be more likely to be diagnosed due to women's issues not being taken as seriously
• Predictive validity is an issue as some schizophrenics are successfully treated whereas others are not, suggesting diagnosis is not valid
• Aetiological validity is an issue as the causes of schizophrenia may be biological or psychological or both, rather than all patients having the same cause
• Cultural bias is an issue, with higher rates of schizophrenia diagnosis for ethnic minorities in the UK compared to their home countries, suggesting symptoms are being misinterpreted
• Rosenhan (1973) study


  Investigated how situational factors affect a diagnosis of schizophrenia, finding that psychiatric staff cannot always distinguish sanity from insanity and that normal behaviour was misinterpreted as 'abnormal' to support the idea that pseudopatients had a mental illness
• Genetics


  The more closely related two people are, the more likely they are to both have schizophrenia, suggesting a genetic basis. Schizophrenia is polygenic and aetiologically heterogeneous.
• Ripke (2014) found 108 variations of genetic combinations associated with an increased risk of schizophrenia in 37,000 patients
• Gottesman (1991) found concordance rates of 48% for identical twins and 17% for non-identical twins, compared to 1% for the general population, suggesting a strong genetic basis for schizophrenia
• However, the lack of 100% concordance rate between identical twins and the higher rate in dizygotic twins compared to normal siblings suggests something other than genetics must affect whether a person develops schizophrenia
• Brown et al. (2002) found a relationship between paternal age (linked with increased risk of mutation) and the risk of developing schizophrenia, supporting the genetic explanation
• Dopamine hypothesis


  The symptoms of schizophrenia result from an imbalance of the neurotransmitter dopamine across the brain
• Leucht et al (2013) found that treatment of symptoms with drugs that normalise dopamine levels were much more effective than placebo, supporting the dopamine hypothesis
• However, the involvement of other neurotransmitters like glutamate and serotonin challenges the dopamine hypothesis as the sole explanation for schizophrenia
• Neural correlates


  Correlations between neuronal structures and positive or negative symptoms of schizophrenia
• One limitation is that there is mixed support for the dopamine hypothesis
• Dopamine agonists (eg: amphetamines) that increase dopamine levels have been found to induce schizophrenia-like symptoms in the people who do not have the disorder
• Antipsychotics (eg: chlorpromazine) that reduce the availability of dopamine receptors have been found to reduce the severity of the symptoms
• This supports the role of dopamine in causing the symptoms of schizophrenia
• However, challenging this is that some candidate genes that increase the risk of schizophrenia have been found to code for the neurotransmitter glutamate
• This suggests dopamine does not provide a full explanation for schizophrenia and that it may actually only be one of many major factors involved
• This reduces the validity of the dopamine hypothesis as it may not be only dopamine that we are measuring as a cause
• Neural correlates


  Correlations between neuronal structures and positive or negative symptoms
• Ventricle size


  The ventricles are internal brain cavities that contain and produce Cerebrospinal fluid. CSF provides a cushioning effect that protects the brain from damage when we receive knocks to the head
• A strength is that the research into enlarged ventricles and neurotransmitter levels have high reliability