Estimating cognitive impairment in bipolar disorder: should we account for premorbid IQ
Author(s)
Type
Journal Article
Abstract
Introduction: Cognitive impairment estimations traditionally rely on the deviation of current cognitive performance from population norms (normative approach). Since bipolar disorder (BD) has been associated with above-average premorbid cognitive functioning in some studies, this approach might underestimate the extent of cognitive impairment in a proportion of patients. We examined whether intraindividual deviation of cognitive performance from premorbid estimates (idiographic approach) would more accurately estimate impairment in BD and assessed the functional relevance of this approach.
Methods: This study pooled euthymic patients with BD (N=257) taking part in two cognitive remediation trials with comparable eligibility criteria and measures. All participants underwent a baseline assessment including measures of current cognition, premorbid IQ, psychosocial functioning, and mood symptom severity. We estimated and compared prevalence of normative versus idiographic impairment and examined the association of the idiographic approach with functioning.
Results: According to normative standards, 13-31% of our euthymic sample was classified as cognitively impaired depending on the adopted cut-off. After accounting for premorbid IQ, idiographic impairment rates increased to 37-64%. The difference between the two approaches was significant for each cut-off considered (0.5 and 1 SD). Idiographic cognitive impairment was significantly associated with psychosocial functioning, even after controlling for residual mood symptoms and demographic/clinical variables, and functional impairment classification.
Conclusion: Common practices to characterizing cognitive impairment using a normative approach may underestimate the extent of impairment for a substantial proportion of euthymic patients with BD. Considering idiographic impairment provides an alternative, functionally relevant approach for cognition trials and clinical practice.
Methods: This study pooled euthymic patients with BD (N=257) taking part in two cognitive remediation trials with comparable eligibility criteria and measures. All participants underwent a baseline assessment including measures of current cognition, premorbid IQ, psychosocial functioning, and mood symptom severity. We estimated and compared prevalence of normative versus idiographic impairment and examined the association of the idiographic approach with functioning.
Results: According to normative standards, 13-31% of our euthymic sample was classified as cognitively impaired depending on the adopted cut-off. After accounting for premorbid IQ, idiographic impairment rates increased to 37-64%. The difference between the two approaches was significant for each cut-off considered (0.5 and 1 SD). Idiographic cognitive impairment was significantly associated with psychosocial functioning, even after controlling for residual mood symptoms and demographic/clinical variables, and functional impairment classification.
Conclusion: Common practices to characterizing cognitive impairment using a normative approach may underestimate the extent of impairment for a substantial proportion of euthymic patients with BD. Considering idiographic impairment provides an alternative, functionally relevant approach for cognition trials and clinical practice.
Date Issued
2026-05-01
Date Acceptance
2025-06-03
Citation
Acta Psychiatrica Scandinavica, 2026, 153 (5), pp.468-476
ISSN
0001-690X
Publisher
Wiley
Start Page
468
End Page
476
Journal / Book Title
Acta Psychiatrica Scandinavica
Volume
153
Issue
5
Copyright Statement
© 2025 The Author(s). Acta Psychiatrica Scandinavica published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
10.1111/acps.70000
Subjects
bipolar
cognitive impairment
functioning
premorbid IQ
Publication Status
Published
Date Publish Online
2025-06-18