Neurocognitive functioning during symptomatic states and remission in bipolar disorder and schizophrenia: A comparative study
Introduction
Cognitive dysfunction is one of the most common characteristics of both bipolar disorder and schizophrenia and is associated with poorer functional outcomes in both disorders (Lee et al., 2015). Cognitive dysfunction has been identified as a core feature of schizophrenia and is associated with level of functioning and symptomatic remission in schizophrenia (Bora et al., 2010). However, neurocognitive dysfunction appears in multiple cognitive domains during mania and depression and persists even in euthymia in bipolar disorder (Arts et al., 2008; Bora et al., 2009a; Bora and Pantelis, 2015; Bourne et al., 2013; Hidiroğlu et al., 2015; Mann-Wrobel et al., 2011; Robinson et al., 2006; Torres et al., 2007). Meta-analyses comparing the disorders in terms of neurocognitive functioning have demonstrated significantly milder cognitive impairment in bipolar disorder than in schizophrenia, with a moderate effect size (Bora et al., 2009a; Bora and Pantelis, 2015; Krabbendam et al., 2005), and have suggested relatively milder and more heterogeneous neurocognitive deficits in bipolar disorder relative to schizophrenia (Bora, 2015; Bora et al., 2009b; Krabbendam et al., 2005).
The remission state is related to improved cognitive outcomes in both disorders. A limited number of studies have grouped patients with schizophrenia according to its symptomatic remission criteria, identified by The Remission in Schizophrenia Working Group (Andreasen et al., 2005). These studies have indicated that symptomatically remitted schizophrenia patients present persistent but milder neurocognitive deficits in comparison to those without remission (Brissos et al., 2011; Fukumoto et al., 2014; Hofer et al., 2011; Kurebayashi and Otaki, 2018; Yun et al., 2011). However, patients with bipolar disorder present more prominent cognitive impairments in acute states of bipolar disorder (i.e., manic, hypomanic, depressive, or mixed episodes) than those in euthymia (Basso et al., 2002; Bora et al., 2006; Ha et al., 2014; Martínez-Arán et al., 2000) and demonstrate better executive performance after remission of manic symptoms (McGrath et al., 1997; Murphy et al., 2001, 1999). The only meta-analysis focusing on neurocognition across different mood episodes revealed that bipolar disorder patients in a manic/mixed episode performed more poorly in verbal learning and fluency compared to those in an euthymic state (Kurtz and Gerraty, 2009).
The severity of the psychotic symptoms has been associated with poorer neurocognitive performance in both disorders. Psychotic symptoms are the core characteristic of schizophrenia, but are also common in bipolar disorder; nearly 70% of patients with bipolar disorder type I have a history of psychotic symptoms (Keck et al., 2003; Özyıldırım et al., 2010). A history of psychosis is associated with relatively more severe cognitive impairments in bipolar disorder (Bora, 2018; Trisha et al., 2018), and has been shown to better predict neurocognitive dysfunction in bipolar disorder than a diagnosis of bipolar disorder type I (Bora et al., 2010). Acute psychosis might have an even more significant impact on cognitive functioning in bipolar disorder (Levy and Weiss, 2010). Similarly, patients with schizophrenia present improvements in cognitive performance after dissolution of an acute psychotic relapse (McGrath et al., 1997; Trampush et al., 2015).
An earlier study suggested that the pattern of improvement in neurocognitive functions between acute and subacute states differed between patients with schizophrenia versus patients with mania (McGrath et al., 1997). For example, between the acute and subacute states, patients with mania improved significantly on their Wisconsin Card Sorting Test categories-achieved score, whereas patients with schizophrenia improved their Stroop or Trail Making Test scores (McGrath et al., 1997). More recent studies investigating the neurocognitive impairment differences between acutely ill patients with bipolar disorder and those with schizophrenia have suggested milder deficits in psychotic mania compared to symptomatic patients with schizophrenia (Lewandowski et al., 2013; Zanelli et al., 2010). However, interaction of illness (bipolar disorder or schizophrenia) and state (remitted or symptomatic) is an underexplored area in studies comparing neurocognitive performance between bipolar disorder and schizophrenia, which focus mainly on clinically stable or symptomatically remitted patients (Bora et al., 2009a; Bora and Pantelis, 2015; Krabbendam et al., 2005; Stefanopoulou et al., 2009).
In this study, we aim to compare cognitive dysfunction in bipolar disorder and schizophrenia during the remission and the symptomatic states. We hypothesize that both illness and state will have significant disruptive effects on the neurocognitive performance in patients with bipolar disorder and schizophrenia
Section snippets
Participants
The study included males and females 18–65 years of age who met DSM-IV criteria for bipolar disorder type I (n = 76), or schizophrenia (n = 80). The bipolar disorder group consisted of symptomatic patients in a manic episode with psychotic features (n = 32) or remitted patients (euthymic for at least 6 months) with a history of mood episodes with psychotic features (n = 44). The schizophrenia group consisted of patients in symptomatic (n = 41) and remission (schizophrenia remission, n = 39)
The symptomatic remission status
The symptomatic remission status of two diagnoses were evaluated separately using the Young Mania Rating Scale (Karadağ et al., 2002), Hamilton Depression Scale-17 (Akdemir et al., 2001), a Structured Clinical Interview for the DSM-IV-TR Axis I Disorders (SCID-I) for bipolar disorder, and the Positive and Negative Symptom Scale (Kostakoğlu et al., 1999). The Clinical Global Impression Scale (CGI) (Busner and Targum, 2007) was used to measure symptom severity in both groups.
Euthymia in bipolar
Clinical characteristics of the study groups
Demographic and clinical features of the study groups are given in Table 1. Among the patient groups, 57.9% of patients with bipolar disorder (n = 44) and 48.8% of patients with schizophrenia were remitted (p = .253). Mean age, age of illness onset, and levels of education were similar among all the groups (Table 1). There were significant differences with respect to sex distribution, duration of illness, CGI, and chlorpromazine equivalents (Table 1). Remitted patients with bipolar disorder had
Discussion
An illustration of patterns of neurocognitive variations regarding illness states in bipolar disorder and schizophrenia is of great interest because of its potential for contributing to specific interventions for neurocognitive decline in both disorders. In the present study, we compared a global cognition factor, which explained 51.47% of variance, and results from a comprehensive battery of neurocognitive tests in patients with schizophrenia and bipolar disorder type I with a history of
Conclusion
In the present study, we compared cognitive functions in patients with schizophrenia and bipolar disorder with a history of psychosis, during remission and symptomatic states. Our data suggest that deficits in global cognition and verbal fluency were milder in bipolar disorder than in schizophrenia, regardless of remission and symptomatic states. Deficits in global cognition and working memory were associated with the symptomatic states in both bipolar disorder and schizophrenia. Furthermore,
Author contributions
D.C., A.A., C.H.O., B.B.A., Z.T and K.A. were responsible for the clinical interviews and cognitive assessments. D.C. and E.B. conducted the statistical analyses. D.C. wrote the first draft. All authors contributed to the planning of the study. All authors critically reviewed the paper. All authors contributed to and have approved the final manuscript.
Declaration of Competing Interest
The authors have no conflicts of interest regarding subject of this manuscript. D.C., E.B., B.A., K.A and A.Ö. receive research supports from the Scientific and Technological Research Council of Turkey (TUBITAK). The other authors do not have any conflicts of interest.
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