Mind the gap: The impact of discrepancy between current cognitive function and premorbid intelligence on psychosocial functioning in older age bipolar disorder

Abstract

Introduction: A discrepancy between current cognitive performance and premorbid IQ may indicate cognitive decline and relate to poorer psychosocial functioning in bipolar disorder, even when cognition appears unimpaired by standard norms. This study examined how objective cognition and IQ-cognition discrepancy relate to psychosocial functioning in older age bipolar disorder (OABD). Methods: OABD underwent neurocognitive assessment, intelligence quotient (IQ) estimation (using vocabulary subtest of WAIS-III), and psychosocial functioning assessment via the Functioning Assessment Short Test (FAST). IQ-cognition discrepancy scores were calculated as the difference between current cognitive performance and estimated premorbid IQ (range: -10 to +10; negative values indicating possible cognitive decline). Linear regressions examined associations between cognition, discrepancy score, and psychosocial functioning. Discriminant analyses evaluated the ability of these scores to predict functional impairment. Results: The sample included 165 participants (116 OABD and 49 healthy controls). Poorer cognitive performance was significantly associated with worse psychosocial functioning (β = -3.38, p = .002). Greater IQ-cognition discrepancy also predicted worse functioning (β = -0.92, p = .04), though cognitive performance showed a stronger association (β = -2.93, p = .017) and better discriminative ability for functional impairment (AUC = 0.75; cut-off = -0.4 SD; sensitivity = 0.69; specificity = 0.72) compared to discrepancy score (AUC = 0.64; sensitivity = 0.39; specificity = 0.87). Conclusions: IQ-cognition discrepancy may serve as a useful idiographic marker of functional impairment in OABD, particularly for individuals with high premorbid IQ. Its use could enhance clinical decision-making and broaden inclusion in pro-cognitive intervention trials.