Research paperThe association of duration and severity of disease with executive function: Differences between drug-naïve patients with bipolar and unipolar depression
Introduction
Bipolar disorder (BD) is a common and severe psychiatric illness with the characteristics of high morbidity, high recurrence rate, and high disability. Data from a nationally representative survey in the United States demonstrated that the lifetime and 12-month prevalence of BD were 2.8 and 4.5%, respectively (Merikangas et al., 2007). The global burden of diseases survey (GBD) showed that the years lived with disability (YLDs) of BD and unipolar depression (UPD) increased by 14.9 and 17.8% from 2005 to 2015 respectively, becoming the 21st and 3rd causes of global burden of diseases (Disease et al., 2016).
Patients with BD may experience four mood states, which include major depressive episodes, hypomanic/manic episodes, and euthymia. However, the clinical symptoms of a BD depressive episode, also known as bipolar disorder depression (BDD), are similar to those of UPD. Therefore, BDD is often undiagnosed or misdiagnosed in clinical practice. A previous investigation conducted by Smith et al. (2011) demonstrated that 3.3–21.6% patients previously diagnosed as UPD could be diagnosed as BD. The result from a Chinese survey also showed that the misdiagnosis rate of BD was up to 20.8%, in which bipolar I disorder was 7.9% and bipolar II disorder was 12.9% respectively (Pan et al., 2014). This issue might lead to treatment delays or even harmful treatment. For example, unrecognized BDD patients might be prescribed antidepressants in the absence of mood stabilizers (Hughes et al., 2016, Wang et al., 2014). Hence, understanding the characteristic differences between BDD and UPD can provide clues to clinicians for the differential diagnosis of both disorders.
In addition, it is noteworthy that cognitive impairment is a key factor in reducing the learning and occupational abilities of patients with BDD and UPD (Bonnin et al., 2014, Woo et al., 2016), and an important factor increasing the burden of disease. Previous studies indicated that cognitive function, especially executive function, was decreased significantly in BDD and UPD patients during acute episodes and may persist into euthymic periods (Santos et al., 2014, Xu et al., 2012). Moreover, there were differences in cognitive impairment between the two disorders. Patients with BDD performed significantly worse in domains of verbal fluency and executive function than UPD patients (Xu et al., 2012). In addition, researchers found that cognitive function was affected by various psychotropic medications (Keefe et al., 2014), which could bias the results of cognitive studies. Several studies suggested that measures of executive function in unmedicated BD patients (patients who were previously treated but discontinued medications in recent weeks or months), such as response inhibition and working memory, were not significantly different from healthy controls (Penfold et al., 2015, Taylor Tavares et al., 2007). However, the features of executive function impairment in drug-naïve patients with mood disorders (patients who have never been treated) remain unclear. Consequently, we conducted this research to investigate the characteristic differences in executive function impairment between BDD and UPD patients before they were treated with psychotropics, and to explore the associations with relevant clinical attributes.
Section snippets
Subjects
Outpatients/inpatients with BDD or UPD were recruited from the division of mood disorders, Shanghai Mental Health Center, from December 2014 to March 2017. The Institutional Review Board of Shanghai Mental Health Center approved the study. All protocols related to human experiments were conducted in accordance with the Declaration of Helsinki. All participants received a detailed explanation of the study and signed an informed consent (which included potential risks and benefits) before their
Demographic characteristics
30 participants in each group (BDD, UPD and HC) were enrolled in this study. There was no significant difference in socio-demographic characteristics between the three groups, including age (χ2 = 0.009, P = 0.995), education (χ2 = 0.191, P = 0.909), gender, marital status (χ2 = 5.578, P = 0.190), employment status (χ2 = 6.255, P = 0.175) (Table 1).
Clinical characteristics and assessments
Compared with UPD, patients with BDD experienced more mood episodes (U = 43.000, P < 0.001), more major depressive episodes (U = 234.500, P = 0.021)
Discussion
Executive function impairment is widely reported in BD patients (Cullen et al., 2016). Even in euthymic patients with BD type I, the incidence of executive function impairment was as high as 53.8% in Han Chinese (Eric et al., 2013). Therefore, this issue has received widespread attention of researchers in recent years. However, executive function impairment in drug-naïve patients with BDD has not been well studied.
In the present study, we compared the performance of BDD patients, UPD patients,
Role of the funding sources
This work was supported by the National Key R&D Program of China (2016YFC1307100), the Shanghai Hospital Development Center Foundation (16CR2027B), National High-tech R&D Program (863 Program) (2015AA020509, Ministry of Science and Technology of the People's Republic of China), National Natural Science Foundation of China (91232719, 81201056, 81301159, 81771465), NSFCCIHR(81761128032), Shanghai Health Bureau Excellent Young Talents Program (XYQ2011014), The National Key Clinical Disciplines at
Contributors
JC, YF and TY designed the study. All authors were involved in the study recruitment. TY, JC and XX carried out the statistic analysis. TY and JC wrote the draft. Lam RW polished the manuscript. All authors approved the final draft and agreed to be responsible for all aspects of the work.
Conflict of interest
The authors of this paper do not have any commercial associations that might pose a conflict of interest in connection with this manuscript.
Acknowledgments
We sincerely thank all the participants of this study.
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