Effect of alcohol and illicit substance use on verbal memory among individuals with bipolar disorder

Background Cognitive impairment is a well-established feature of bipolar disorder (BD). Comorbid BD and substance use leads to poor psychosocial and clinical outcomes. However, knowledge on the neurocognitive functioning of individuals with dual diagnosis is limited. The aim of this study is to assess the cognitive performance of subjects with BD, BD with comorbid alcohol use disorder (AUD), and BD with comorbid illicit substance use disorders (SUD) as compared to healthy individuals. Methods We included 270 inpatients and outpatients with BD and 211 healthy controls. The diagnostic of BD and substance use disorder was assessed using the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders Axis I. Demographic and clinical information were also collected. The cognitive assessment included the Wechsler Test of Adult Reading (WTAR), and a revised version of the California Verbal Learning Test (CVLT) as part of the South Texas Assessment of Neurocognition (STAN). Results The STAN was administered to 134 BD patients (100 female, M±SD: 37.37±12.74 years), 72 BD patients with AUD (40 female, M±SD: 38.42±11.82), 64 BD patients with SUD (39 female, M±SD: 34.50±10.57), and 211 healthy controls with no lifetime history of mental illness and substance use (127 female, M±SD: 34.80±12.57 years). In terms of clinical characteristics, BD+SUD showed a marginally earlier onset of illness compared to BD. Compared to HC, BD performed poorly in the immediate recall and short-delay free tests of the CVLT, while BD patients with AUD and SUD showed significant memory deficits in both the immediate recall and recognition components of the CVLT. There were no differences in memory performance between BD and BD with either AUD or SUD. Conclusions A history of substance use disorders is associated with an earlier onset of BD. BD has marked effects on processes underlying the encoding of new information, while comorbid substance use in BD impairs more specifically the recognition of previously presented information. Future longitudinal studies should evaluate the effects of AUD and SUD on illness progression and therapeutic outcomes.