As discussed by Gold, 40 one alternative approach to increasing the diagnostic specificity of cognitive impairment would be to use a more conservative criterion eg 2 SDs below the norm. However, more stringent criteria would also decrease the sensitivity of detecting cognitive impairments in clinical populations. Even in the severely impaired sample of Wilk et al, 42 only half of the patients performed below 2 SDs from the norm.
In fact, results of meta-analyses conducted in schizophrenia would estimate that an even smaller percentage of patients would meet impairment criteria given such a stringent threshold.
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There is evidence indicating that subjects who later develop schizophrenia have cognitive impairment during their childhood and adolescence. Nevertheless, early cognitive decline may not differentiate between schizophrenia and affective psychoses due to the fact that IQ deficits in early adolescence are observed only in a subgroup of patients who later go on to develop schizophrenia. Nevertheless, according to this study, only half of the patients could be considered to have had a premorbid intellectual impairment.
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Furthermore, this ratio was probably an overestimate because the study sample was biased toward inclusion of more severe cases and male patients. These findings suggest that while early cognitive decline is potentially specific to schizophrenia, it is not common enough to reliably differentiate between most cases of schizophrenia and affective psychoses. As discussed above, defining the severity and prevalence of cognitive impairment would not help to differentiate schizophrenia from other major psychoses due to the significant overlap of cognitive performance between syndromes.
Further, because early intellectual decline is a characteristic limited to a subgroup of patients with schizophrenia, it would also serve little use in differentiating between these disorders. Emphasizing stability of the cognitive impairment would not be a solution either, as cognitive deficits persist regardless of symptom state in both schizophrenia ie, following resolution of first-rank symptoms and BD ie, during periods of euthymia.
Therefore, we suggest that introducing cognitive impairment as an inclusion criterion for diagnostic purposes would not serve to increase the point of rarity between the major psychoses. As Keefe and Fenton 1 have suggested, it could still be desirable to include cognition in the diagnostic criteria of schizophrenia as this may effectively increase the awareness of cognitive dysfunction in clinical practice.
Inclusion of cognitive impairment criteria could also pave the way for research efforts to focus more explicitly on treatment avenues targeting cognitive remediation. The emphasis that Keefe and Fenton 1 place on recognizing the stability of cognitive deficits over time and the importance of decline from premorbid levels of cognitive functioning is also important. Firstly, they may have considered cognitive impairment as a gateway criterion for the diagnosis of the disorder.
One potential problem with this approach, however, is that it would result in the reclassification of substantial numbers depending on the severity of impairment incorporated in the definition of schizophrenia patients who would no longer meet diagnostic criteria for the disorder. Conversely, it is also possible that Keefe and Fenton 1 only considered adding cognitive impairment as a criterion within section A of DSM-V.
This change would not necessarily influence the diagnosis of patients with cognitive impairment. However, for those patients who were cognitively intact, it would be more difficult to satisfy criteria for the disorder eg, if 3 clinical symptoms were required as compared with the current 2. This approach would still lead to a reclassification of some, but not all, patients with schizophrenia who were not cognitively impaired. To our knowledge, the psychosis working group for DSM-V is not advocating the inclusion of cognition as part of the diagnostic criteria for schizophrenia.
However, there may be several alternative ways to include cognitive impairment in the diagnostic classification of schizophrenia.
One approach would involve the use of cognitive impairment as a specifier, rather than an inclusion criterion. This is similar to the current practice used in obsessive-compulsive disorder of further classifying the syndrome using insight as a specifier. This approach would increase attention to, and awareness of, cognitive deficits in schizophrenia without causing diagnostic shifts. A second alternative would involve adoption of a dimensional approach to clinical classification. While replacing the categorical classification system with a dimensional approach represents one possibility to refining the current diagnostic system, such a radical option is unlikely to be accepted at this stage.
However, a more feasible change is one in which the classification system is based on a hybrid model of categorical and dimensional approaches. In both alternatives, cognitive impairment would be represented as one of the dimensions within the system. In a hybrid system, a patient meeting diagnostic criteria for schizophrenia would be further defined according to the severity of their symptoms within different dimensions such as positive and negative symptoms and cognitive impairment.
Akin to using cognitive impairment as a specifier, this approach would prevent diagnostic shifts based on cognitive impairments. We contend that, at this stage, DSM-V should certainly include cognitive impairment in the diagnostic classification of schizophrenia but through means that would not exclude cases based on their relatively preserved cognitive abilities.
We suggest that incorporating cognitive impairment either as a specifier or as a dimension within a hybrid classification system would provide the most appropriate means of satisfying this agenda. Additionally, in line with Keefe and Fenton, 1 the state independent nature of the cognitive deficits should be emphasized, and the severity of the impairment should be clearly defined.
Looking to the future, the addition of cognitive impairment as an inclusion criterion for schizophrenia should not be considered until such time as there is consistent evidence for a specific impairment that can differentiate between the major psychoses. At present, it is unlikely that cognitive impairment can help to differentiate schizophrenia from mood disorders based on current diagnostic boundaries.
This does not necessarily mean that we should consider major psychoses, including affective psychoses and schizophrenia as a unitary concept. The potential utility of cognitive testing as a tool to better understand heterogeneous entities within the major psychoses and schizophrenia should be tested rigorously. While historically there has been some suggestion that poor functioning schizophrenia cases should be differentiated from patients with better prognoses ie, type 1 and 2 schizophrenia , 49 , 50 these subtypes have been thought to lack validity and stability.
Cognitive Decline Over Time in Schizophrenia and Other Psychoses
In that case, the inclusion of specific cognitive criteria may be helpful in distinguishing between subtypes of these disorders. Alternatively, cognitive deficits could prove to be a common dimension of all major psychoses that differ only in relative severity. Finally, we suggest that cognitive impairment should also be considered as a specifier of BD and psychotic depression. There is already sufficient evidence supporting the stability and persistence of cognitive deficits in euthymic patients with BD, and currently available literature points toward consistent cognitive impairment in late-onset depression.
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Cognitive deficits and functional outcome in schizophrenia
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Close mobile search navigation Article Navigation. Volume Article Contents. Diagnostic Differences in Cognition. How to Define Cognitive Impairment in Schizophrenia? Over follow-up, patients with other psychoses also showed small declines in memory and vocabulary relative to controls but no declines in IQ or other domains. This study did not examine other potential contributors to cognitive decline, including smoking, other substance use, or comorbid illnesses.
Nevertheless, the findings suggest that the cognitive deficits seen in early psychosis are not static and that impairments and their changes over time occur differentially across psychotic conditions.
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Cognitive remediation, especially focusing on memory and vocabulary, might particularly benefit patients with severe symptoms. Zanelli J et al. Cognitive change in schizophrenia and other psychoses in the decade following the first episode. Am J Psychiatry Jul 1; [e-pub]. Get Your Copy. Am J Psychiatry Jul 1 Decline in several cognitive domains continues for a decade after disease onset and is not attributable to medication effects. Comment This study did not examine other potential contributors to cognitive decline, including smoking, other substance use, or comorbid illnesses. The order in which the cards are presented and the rules used to guide decisions are summarized in this table:.
While this is early data it does provide a basis for further refinement of approaches and methods for identifying cognitive impairment in people with this debilitating illness. This could help us learn much more about the day to day fluctuations of cognition in patients with schizophrenia than was previously possible. Publications Presentations Webinars Blog.
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