How should DSM-V criteria for schizophrenia include cognitive impairment?

Abstract

Neurocognitive impairment is considered a core component of schizophrenia and is increasingly under investigation as a potential treatment target. On average, cognitive impairment is severe to moderately severe compared with healthy controls, and almost all patients with schizophrenia demonstrate cognitive decrements compared with their expected level if they had not developed the illness. Compared with patients with affective disorders, cognitive impairment in schizophrenia appears earlier, is more severe, and tends to be more independent of clinical symptoms. While the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, description of schizophrenia includes several references to cognitive impairment, neither the diagnostic criteria nor the subtypology of schizophrenia include a requirement of cognitive impairment. We forward for consideration a proposal that the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, criteria include a specific criterion of "a level of cognitive functioning suggesting a consistent severe impairment and/or a significant decline from premorbid levels considering the patient's educational, familial, and socioeconomic background." The inclusion of this criterion may increase the "point of rarity" with affective psychoses and may increase clinicians' awareness of cognitive impairment, potentially leading to more accurate prognosis and better treatment outcomes. Future research will need to address the validity of these possibilities. The reliable determination of cognitive impairment as part of a standard diagnostic evaluation may present challenges to diagnosticians with limited resources or insufficient expertise. Various cognitive assessment methods for clinicians, including brief assessments and interview-based assessments, are discussed. Given the current emphasis on the development of cognitive treatments, the evaluation of cognition in schizophrenia is an essential component of mental health education.

Fig. 1.

Cognitive Profiles in Schizophrenia, Major Depression, and Euthymic Bipolar Disorder From Published Meta-analyses. Data from Heinrichs and Zakzanis, Zakzanis et al, and van Gorp et al Healthy group mean = 0. Verb Mem (D), delayed verbal memory; Verb Mem (I), immediate verbal memory; Vis Mem, visual memory; Trails B, Trail Making Test, B; WCST, Wisconsin Card Sorting Test; BD, Wechsler Adult Intelligence Scale (WAIS) block design test; Voc, WAIS vocabulary. Reprinted with permission from Buchanan et al..

Fig. 2.

Distributions of Total Scores on the Repeatable Battery for the Assessment of Neuropsychological Status in Patients With Schizophrenia and Healthy Controls From Published Norms. Reprinted with permission from Randolph et al and Wilk et al.

Fig. 3.

Expected Neurocognitive Performance Based on Maternal Education of Healthy Controls. Reprinted with permission from Keefe et al.

Fig. 4.

Standardized Scholastic Test Performance in Grades 4, 8, and 11 Relative to State Norms for 70 Subjects Who Later Developed Schizophrenia. Reprinted with permission from Fuller et al.