The impact of premorbid and current intellect in schizophrenia: cognitive, symptom, and functional outcomes

Abstract

Background:Cognitive heterogeneity among people with schizophrenia has been defined on the basis of premorbid and current intelligence quotient (IQ) estimates. In a relatively large, community cohort, we aimed to independently replicate and extend cognitive subtyping work by determining the extent of symptom severity and functional deficits in each group.Methods:A total of 635 healthy controls and 534 patients with a diagnosis of schizophrenia or schizoaffective disorder were recruited through the Australian Schizophrenia Research Bank. Patients were classified into cognitive subgroups on the basis of the Wechsler Test of Adult Reading (a premorbid IQ estimate) and current overall cognitive abilities into preserved, deteriorated, and compromised groups using both clinical and empirical (k-means clustering) methods. Additional cognitive, functional, and symptom outcomes were compared among the resulting groups.Results:A total of 157 patients (29%) classified as ‘preserved’ performed within one s.d. of control means in all cognitive domains. Patients classified as ‘deteriorated’ (n=239, 44%) performed more than one s.d. below control means in all cognitive domains except estimated premorbid IQ and current visuospatial abilities. A separate 138 patients (26%), classified as ‘compromised,’ performed more than one s.d. below control means in all cognitive domains and displayed greater impairment than other groups on symptom and functional measures.Conclusions:In the present study, we independently replicated our previous cognitive classifications of people with schizophrenia. In addition, we extended previous work by demonstrating worse functional outcomes and symptom severity in the compromised group.

Cognitive Heterogeneity across Schizophrenia and Bipolar Disorder: A Cluster Analysis of Intellectual Trajectories

“…The preserved group is defined by a premorbid IQ score > 90 and < 10 points of decline from premorbid to current IQ, the deteriorated group has ≥ 10 IQ points decline, and the compromised group has a premorbid IQ < 90 (and a IQ decline < 10 points) (Weickert et al, 2000). Studies using this clinical classification method have confirmed the groups using empirical clustering methods (Weickert et al, 2000;Wells et al, 2015). The subgroups have been shown to differ in cognitive profile (Weickert et al, 2000;Wells et al, 2015), functional outcome (Wells et al, 2015), symptom profile (Wells et al, 2015), and brain volume or cortical thickness (Weinberg et al, 2016;Van Rheenen et al, 2018).…”

Cognitive Subtypes of Schizophrenia Characterized by Differential Brain Volumetric Reductions and Cognitive Decline

“…These findings were recently replicated in a large independent sample of 534 chronically ill patients with schizophrenia and 635 healthy controls. 4 These IQbased subgroups were also identified in similar proportions of individuals with first-episode psychosis. 5,6 Despite the identification of unique, intellectually based subgroups, the nature and extent of cognitive deficits in these subgroups remain somewhat unclear because investigators 3,[7][8][9][10] have found that even those with putatively preserved IQ perform significantly worse than matched healthy individuals on a range of cognitive abilities.…”

Exploring Heterogeneity on the Wisconsin Card Sorting Test in Schizophrenia Spectrum Disorders: A Cluster Analytical Investigation

“…Through identifying distinct clusters of participants who share a homogenous cognitive profile, several subgroups that characterise the within-group cognitive variability prevalent among people with psychosis have been consistently identified. Broadly, two anchoring cognitive profiles repeatedly emerge, a severely impaired subgroup and a cognitively intact subgroup, with a varying number of intermediate profiles of mixed/specific cognitive deficits emerging in-between (Burdick et al, 2014;Lewandowski et al, 2018;Van Rheenen et al, 2017;Weickert et al, 2000;Wells et al, 2015). These subgroups can be identified at first episode (Reser et al, 2015;Uren et al, 2017), transcend the familial and psychosis spectrum (Burdick et al, 2014;Hoti et al, 2004;Lewandowski et al, 2014;Van Rheenen et al, 2017), exhibit distinctive brain structure (Czepielewski et al, 2017;Van Rheenen et al, 2018;Woodward & Heckers, 2015), and display altered response to treatment and functional outcomes (Gilbert et al, 2014;Uren et al, 2017).…”