Role of cognitive reserve in cognitive variability in euthymic individuals with bipolar disorder: cross-sectional cluster analysis

Abstract

Background People with bipolar disorder have moderate cognitive difficulties that tend to be more pronounced during mood episodes but persist after clinical remission and affect recovery. Recent evidence suggests heterogeneity in these difficulties, but the factors underlying cognitive heterogeneity are unclear. Aims To examine whether distinct cognitive profiles can be identified in a sample of euthymic individuals with bipolar disorder and examine potential differences between subgroups. Method Cognitive performance was assessed across four domains (i.e. processing speed, verbal learning/memory, working memory, executive functioning) in 80 participants. We conducted a hierarchical cluster analysis and a discriminant function analysis to identify cognitive profiles and considered differences in cognitive reserve, estimated cognitive decline from premorbid cognitive functioning, and clinical characteristics among subgroups. Results Four discrete cognitive profiles were identified: cognitively intact (n = 25; 31.3%); selective deficits in verbal learning and memory (n = 15; 18.8%); intermediate deficits across all cognitive domains (n = 30; 37.5%); and severe deficits across all domains (n = 10; 12.5%). Cognitive decline after illness onset was greater for the intermediate and severe subgroups. Cognitive reserve scores were increasingly lower for subgroups with greater impairments. A smaller proportion of cognitively intact participants were using antipsychotic medications compared with all other subgroups. Conclusions Our findings suggest that individuals with cognitively impaired profiles demonstrate more cognitive decline after illness onset. Cognitive reserve may be one of the factors underlying cognitive variability across people with bipolar disorder. Patients in the intermediate and severe subgroups may be in greater need of interventions targeting cognitive difficulties.

Inflammatory biomarkers and cognitive functioning in individuals with euthymic bipolar disorder: exploratory study

“… 30 These essentially measure global cognitive performance as a continuous measure, and cognitive impairment as a classified (dichotomous) construct. 39 The continuous measure of ‘global’ cognitive performance (higher scores indicating less impairment) is calculated from eight cognitive tests across four domains: processing speed (using the Digit Symbol Substitution Test and symbol search (Wechsler Adult Intelligence Scale) 40 ), working memory (using the digit span (Wechsler Adult Intelligence Scale) 40 ), verbal learning and memory (from the verbal paired associates tests I and II (Wechsler Memory Scale) 41 ), and executive functioning (from the Hotel test, 42 matrix reasoning (Wechsler Abbreviated Scale of Intelligence) 43 and verbal fluency F-A-S test 44 ). For each test, the raw score was transformed into standardised normative scores (correcting for age and education) as per test manuals, and the composite global score was then calculated by averaging each participant's z -scores across individual cognitive tests.…”

“…For each test, the raw score was transformed into standardised normative scores (correcting for age and education) as per test manuals, and the composite global score was then calculated by averaging each participant's z -scores across individual cognitive tests. 4 The binary summary variable representing clinically significant cognitive impairment 30 categorises participants scoring ≥1 s.d. below published norms on two or more of the aforementioned cognitive tests as impaired and others as unimpaired.…”

“… 3 A critical contributing factor to disability in bipolar disorder is cognitive impairment, which frequently persists even during periods of euthymic mood. 4 , 5 These deleterious effects of cognitive dysfunction on quality of life are widespread, ranging from everyday psychosocial functioning (including occupational, household and social function), 5 core illness outcomes (e.g. number and severity of affective episodes, including hospital admission rate) 5 and suicidal ideation.…”

Cognition in mood disorders

“…These have generally characterised three or four profiles, of which one has been a group of patients with relatively normal cognitive function compared with population norms or healthy controls, whereas one group has generally been characterised by global cognitive impairment. In Tsapekos et al 9 (this series), to attempt to understand the predictors of these cognitive profiles, four separate profiles were identified in patients with bipolar disorder. Interestingly, but perhaps not surprisingly, lower cognitive reserve was associated with membership of higher impairment groups.…”

A randomised controlled trial of psychotherapy and cognitive remediation to target cognition in mood disorders

“…Cognitive impairment in mood disorders (major depressive disorder, MDD, and bipolar disorder, BD) is evident in a substantial portion of patients, 1,2 across a range of domains (memory, executive function, attention, processing speed) 3,4 . Significant heterogeneity in cognitive profiles exists across the mood disorder spectrum, with some patients affected across all cognitive domains, some affected on specific cognitive domains, and some showing no cognitive impairment 1,2,5 . In general, however, the degree and proportion of patients affected is greater in BD 3 .…”