Neurocognitive impairment in patients with co-occurring bipolar disorder and alcohol dependence upon discharge from inpatient care

Abstract

The current study explored the neurocognitive functioning of patients with co-occurring bipolar disorder and alcohol dependence upon discharge from inpatient care. The study compared scores of neuropsychological tests among three groups of bipolar I inpatients without a history of neurological injury or illness: 1) patients meeting DSM-IV diagnostic criteria for alcohol dependence in the past 6 months (n = 13), 2) patients diagnosed with alcohol dependence in full remission (n = 9), and 3) patients without a history of a substance use disorder (SUD; n = 41). Analyses indicated that patients with co-occurring alcohol dependence exhibited more severe impairment on tests of executive functioning (i.e. Stroop Color–Word Interference Test, Wisconsin Card Sorting Test) than patients without SUD. In addition, the group meeting diagnostic criteria for alcohol dependence in the past 6 months exhibited greater decrements in verbal (California Verbal Learning Test — II) and visual (Rey Complex Figure Test) memory. Analysis further indicated that patients in full SUD remission scored lower on measures of fluid intelligence (Wechsler Abbreviated Scale of Intelligence — Performance IQ). Consistent with previous reports, in the current sample, co-occurring alcohol dependence predicted higher rates of disability status. It is possible that cognitive deficits of greater severity in dually diagnosed patients contribute to this unfavorable outcome. Recognizing the extent of cognitive impairment in dually diagnosed patients may facilitate the effort to ameliorate their condition.

Introduction

Among all major psychiatric disorders, bipolar disorder is associated with the highest prevalence of substance abuse and dependence (Tohen et al., 1998). Patients diagnosed with bipolar and co-occurring substance use disorders (SUD) suffer from a more severe course of illness (Cassidy et al., 2001), poorer long-term recovery (Strakowski et al., 2000), and greater psychosocial disability (Salloum and Thase, 2000). The prevalence and refractory nature of their condition warrants a continued effort to improve the effectiveness of treatment and illness management.

Innovative interventions may be informed by neuropsychological research. Research on the neuropsychology of bipolar disorder generally indicates the presence of significant cognitive impairment persisting into periods of euthymia (Martinez-Aran et al., 2004a), particularly in patients suffering from multiple episodes (Bearden et al., 2001). Similarly, SUDs in general, and alcohol dependence (AD) in particular, are associated with debilitating neuropsychological deficits that do not remit even after enduring periods of abstinence (Paterson, 1998).

Although the neuropsychology of both bipolar disorder and SUDs has been studied extensively, this dual diagnosis condition has largely been ignored. One of the few neuropsychological studies with dually diagnosed patients, who suffered from a range of psychotic disorders, reported unexpected findings, where SUD was associated with better performance on non-verbal cognitive tests and instrumental social role (Carey et al., 2003). However, in a well-controlled study that specifically focused on bipolar disorder and co-occurring AD, Van Gorp et al. (1998) reported additional decrements in executive functioning in dually diagnosed outpatients when compared with controls. It is therefore possible that the neuropsychological deficits associated with both bipolar disorder and AD converge to form impairment of greater severity in patients who suffer from this dual diagnosis. More generally, superimposed on deficits inherent in bipolar disorder, AD may lead to a level of cognitive impairment that interferes with patients' recovery and overall ability to function.

Cognitive deficits in dually diagnosed patients may be most acute during an inpatient admission. The temporal proximity to the peak of both mood disturbance and substance use, coupled with the use of sedating medications over the course of hospitalization, may lead to highly compromised cognitive states at the time of discharge. Underestimating the extent of cognitive impairment in dually diagnosed inpatients can lead to discharge plans that do not fully facilitate recovery.

The current study assessed the cognitive functioning of dually diagnosed patients at the time of discharge from inpatient care. The study compared the scores on neuropsychological measures in bipolar I inpatients with and without alcohol dependence, separating chronic from acute alcohol-related deficits by distinguishing between patients in early and full remission. The hypothesis was that dually diagnosed patients would exhibit more severe cognitive deficits than bipolar I patients without SUD. Among patients with the dual diagnosis, test performance was expected to co-vary with remission state.