NASHVILLE, TN — Processes leading to impairment in schizophrenia and psychotic bipolar disorder might be more similar than previously assumed, according to a new study.
The report in Schizophrenia Research pointed out that neuropsychological impairment is common in schizophrenia and psychotic bipolar disorder, although a common hypothesis is that pathways leading to impairment differ between the two disorders.1
The Vanderbilt University-led study, which also included involvement from the VA’s Tennessee Valley Healthcare System, sought to test several aspects of the hypothesis, which essentially suggests that cognitive impairment in schizophrenia results largely from atypical neurodevelopment, but bipolar disorder is increasingly conceptualized as a neuroprogressive disorder.
To do that, the study team assessed current neuropsychological functioning and estimated premorbid intellectual ability in 260 healthy individuals, as well as in 410 patients who represent a large, cross-sectional sample of individuals in the early and chronic stages of psychosis.
The following hypotheses were tested: 1) cognitive impairment is more severe in schizophrenia in the early stage of psychosis; and 2) cognitive decline between early and chronic stages is relatively greater in psychotic bipolar disorder.
For the study, psychosis patients were classified as either:
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Neuropsychologically normal,
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Deteriorated, or
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Compromised (i.e., below average intellectual functioning).
The issue was whether neuropsychologically compromised and deteriorated patients occurred more often in schizophrenia or psychotic bipolar disorder.
Results indicated that neuropsychological impairment in the early stage of psychosis was more severe in schizophrenia, while psychotic bipolar disorder was not associated with relatively greater cognitive decline between illness stages.
Although the frequency of neuropsychologically compromised patients was higher in schizophrenia, researchers also pointed out that substantial percentages of both schizophrenia and psychotic bipolar disorder patients were classified as neuropsychologically compromised and deteriorated.
“While schizophrenia is associated with relatively greater neurodevelopmental involvement, psychotic bipolar disorder and schizophrenia cannot be strictly dichotomized into purely neuroprogressive and neurodevelopmental illness trajectories; there is evidence of both processes in each disorder,” the study authors concluded.
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Menkes MW, Armstrong K, Blackford JU, Heckers S, Woodward ND. Neuropsychological functioning in early and chronic stages of schizophrenia and psychotic bipolar disorder. Schizophr Res. 2019 Apr;206:413-419. doi:10.1016/j.schres.2018.10.009. Epub 2018 Oct 26. PubMed PMID: 31104720; PubMed Central PMCID: PMC6530584.
