Classification of cognitive performance in bipolar disorder

ABSTRACT

Objective: To understand the etiology of cognitive impairment associated with bipolar disorder, we need to clarify potential heterogeneity in cognitive functioning. To this end, we used multivariate techniques to study if the correlation structure of cognitive abilities differs between persons with bipolar disorder and controls.

Method: Clinically stable patients with bipolar disorder (type I: n = 64; type II: n = 44) and healthy controls (n = 86) were assessed with a wide range of cognitive tests measuring executive function, speed, memory, and verbal skills. Data were analysed with multivariate techniques.

Results: A distinct subgroup (∼30%) could be identified that performed significantly poorer on tests concerning memory function. This cognitive phenotype subgroup did not differ from the majority of bipolar disorder patients with respect to other demographic or clinical characteristics.

Conclusions: Whereas the majority of patients performed similar to controls, a subgroup of patients with bipolar disorder differed substantially from healthy controls in the correlation pattern of low-level cognitive abilities. This suggests that cognitive impairment is not a general trait in bipolar disorder but characteristic of a cognitive subgroup. This has important clinical implications for cognitive rehabilitation and remediation.

KEYWORDS:

• Multivariate analysis
• neuropsychology
• neuropsychological tests
• mood disorders
• bipolar disorder

Acknowledgements

We wish to thank the staff at the St. Göran bipolar affective disorder unit, including coordinator Haydeh Olofsson, study nurses Lena Lundberg and Benita Gezelius. Mathias Kardell is acknowledged for statistical and database support. We also thank the patients and controls participating in this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by grants from the Swedish Medical Research Council (K2014-62X-14647-12-51 and K2010-61P-21568-01-4), the Swedish foundation for Strategic Research (KF10-0039), the Brain foundation, and the Swedish Federal Government under the LUA/ALF agreement (ALF 20130032, ALFGBG-142041).