Recent changes in classification and diagnosis of schizophrenia:
Different subtypes of schizophrenia were there in the past, including:
• Paranoid schizophrenia
• catatonic schizophrenia
• disorganized, or hebephrenic schizophrenia
• schizoaffective disorder
• childhood schizophrenia
In 2013 the Diagnostic and Statistical Manual of Mental Disorders 5th edition (DSM-V) changed the method of classification to bring all these categories under a single heading: schizophrenia.
The decision to eliminate these subtypes was based on the conclusion they had “low reliability, limited diagnostic stability and poor validity.” It was also concluded that they did not provide better treatment or did not predict how patients would respond to treatment. (APA)
Two other important changes that was made to the diagnostic criteria in 2013.
One was the removal of the requirement for a person to experience bizarre delusions and to hear two or more voices talking during an auditory hallucination to receive a positive diagnosis. The second was that, to receive a diagnosis, a person must have at least one of the following symptoms:
• Disorganized speech
Etiology/ RISK FACTORS/CAUSES OF SCHIZOPHRENIA:
Recently, the etiology of schizophrenia is not known. There are various theories regarding its cause. These include:
• a genetic hypothesis,
• cortical disconnection syndrome,
• neurotransmitter dysfunction,
• failure to establish cerebral asymmetry, and
• A neuro-developmental syndrome. It is noted that these possible causes has been linked, and are not considered mutually exclusive. The current thesis focuses on Miller’s (1996, 2008) hypothesis.
1. Miller’s Hypothesis:
There is a strong theme of altered lateralization in the literature on schizophrenia. Miller (1996, 2008) has provided a comprehensive theory that proposes that the underlying enduring abnormal psychological traits observed in people with schizophrenia, as opposed to episodes of active psychosis, can be viewed as the result of an alteration in normal cerebral lateralization. Miller proposes that the functional specialization seen within each hemisphere, namely the location of language in the left hemisphere and visuospatial processing in the right hemisphere (in the right-handed, neurologically normal population) is due to a greater ratio of fast-conducting myelinated and large calibre axons to slow conducting unmyelinated
and small calibre axons in the right hemisphere when compared to the left
hemisphere. This greater ratio of fast conducting axons in the right hemisphere allows for fast parallel processing of visuospatial information. While the greater number of unmyelinated and small calibre axons in the left hemisphere affords the greater temporal resolution needed for speech and language functions located in that hemisphere. Furthermore, Miller proposes that this asymmetry of axonal myelination and calibre type is global within each hemisphere, as opposed to being present only within regions involved in language and visual processing (Miller, 1996). Miller also suggests that callosal projections are made up of axons projecting from one hemisphere to the other. This results in the common finding of faster right-to-left, relative to left-to-right, interhemispheric transfer times (IHTT) in the right-handed normal population (Barnett & Corballis, 2005; Brown, Larson, & Jeeves, 1994; Iwabuchi & Kirk, 2009; Marzi, Bisiacchi, & Nicoletti, 1991; Moes, Brown, & Minnema, 2007; Norwicka, Grabowska, & Fersten, 1996)