Toward the identification of neurocognitive subtypes in euthymic patients with bipolar disorder

Background Cross-sectional and meta-analytic studies showed that patients with bipolar disorder (BD) had neurocognitive impairments even during periods of euthymia. The aim of this study was to estimate the prevalence of BD patients with and without clinically significant cognitive impairments, as well as to analyze clinical and functional variables in these subgroups. Methods Hundred patients with BD and 40 healthy controls were assessed with an extensive neurocognitive assessment. Soft (some cognitive domain with a performance below 1.5 SD of the mean) and hard (at least two domains with values below 2 SD of the mean) criteria were utilized to define clinically significant cognitive impairments. Results Using both soft and hard criteria, the prevalence of clinically significant cognitive impairments was higher in people with BD than in healthy controls. 70% of patients only showed failures of small effect (d=0.21-0.35) in 2 measures of executive functions. Moreover, 30% of patients were indistinguishable from healthy subjects in terms of both neurocognitive and psychosocial functioning. On the contrary, 30% of the sample showed more severe cognitive deficits than those usually reported in literature and had the worst psychosocial functioning. Conclusions The fact that cognitive impairments are very heterogeneous among euthymic patients with BD could contribute to understanding differences in functional outcome. Theoretical and practical implications of these findings are discussed.