J Psychiatry Neurosci 2018;43(4):245-253
Amy J. Lynham, BSc; Leon Hubbard, PhD; Katherine E. Tansey, PhD; Marian L. Hamshere, PhD; Sophie E. Legge, PhD; Michael J. Owen, PhD; Ian R. Jones, PhD; James T.R. Walters, PhD
Background: Cognitive impairments are well-established features of schizophrenia, but there is ongoing debate about the nature and degree of cognitive impairment in patients with schizoaffective disorder and bipolar disorder. We hypothesized that there is a spectrum of increasing impairment from bipolar disorder to schizoaffective disorder bipolar type, to schizoaffective disorder depressive type and schizophrenia.
Methods: We compared performance on the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) Consensus Cognitive Battery between participants with schizophrenia (n = 558), schizoaffective disorder depressive type (n = 112), schizoaffective disorder type (n = 76), bipolar disorder (n = 78) and healthy participants (n = 103) using analysis of covariance with post hoc comparisons. We conducted an ordinal logistic regression to examine whether cognitive impairments followed the hypothesized spectrum from bipolar disorder (least severe) to schizophrenia (most severe). In addition to categorical diagnoses, we addressed the influence of symptom domains, examining the association between cognition and mania, depression and psychosis.
Results: Cognitive impairments increased in severity from bipolar disorder to schizoaffective disorder bipolar type, to schizophrenia and schizoaffective disorder depressive type. Participants with schizophrenia and schizoaffective disorder depressive type showed equivalent performance (d = 0.07, p = 0.90). The results of the ordinal logistic regression were consistent with a spectrum of deficits from bipolar disorder to schizoaffective disorder bipolar type, to schizophrenia/ schizoaffective disorder depressive type (odds ratio = 1.98, p < 0.001). In analyses of the associations between symptom dimensions and cognition, higher scores on the psychosis dimension were associated with poorer performance (B = 0.015, standard error = 0.002, p < 0.001).
Limitations: There were fewer participants with schizoaffective disorder and bipolar disorder than schizophrenia. Despite this, our analyses were robust to differences in group sizes, and we were able to detect differences between groups.
Conclusion: Cognitive impairments represent a symptom dimension that cuts across traditional diagnostic boundaries.
Submitted Apr. 13, 2017; Revised Aug. 12, 2017; Accepted Sept. 11, 2017; Published online first Apr. 5, 2018
Acknowledgments: This work was supported by a Medical Research Council (MRC) PhD studentship to A. Lynham. The work at Cardiff University was funded by MRC Centre (MR/L010305/1) and Program Grant (G0500509). The authors thank Sophie Bishop for her assistance with data collection and participant recruitment. The authors also thank the participants and clinicians who took part in the CoMPaSS study.
Affiliations: From the MRC Centre for Neuropsychiatric Genetics and Genomics, Division of Psychological Medicine and Clinical Neurosciences, School of Medicine, Cardiff University, Cardiff, UK (Lynham, Hubbard, Hamshere, Legge, Owen, Jones, Walters); and the College of Biomedical and Life Sciences, Cardiff University, Cardiff, UK (Tansey).
Competing interests: None declared.
Contributors: A. Lynham, M. Owen and J. Walters designed the study. A. Lynham, S. Legge and J. Walters acquired the data, which A. Lynham, L. Hubbard, K. Tansey, M. Hamshere, S. Legge, I. Jones and J. Walters analyzed. A. Lynham, M. Hamshere, M. Owen, I. Jones and J. Walters wrote the article, which all authors critically reviewed. All authors approved the final version to be published and can certify that no other individuals not listed as authors have made substantial contributions to the paper.
Correspondence to: J.T.R. Walters, MRC Centre for Neuropsychiatric Genetics and Genomics, Division of Psychological Medicine and Clinical Neurosciences, Cardiff University School of Medicine, Hadyn Ellis Building, Maindy Road, Cardiff, CF24 4HQ; waltersJT@cardiff.ac.uk