Compared with the study of QOL in unipolar depression, research into QOL in BD has been sparse.10 However, to date, the literature permits preliminary conclusions on 2 fundamental questions; namely, the degree of QOL impairment in BD patients compared with that in nonclinical and other patient populations, and the differential impact on QOL of the phases of BD.19-22
Several studies have sought to determine the degree of QOL impairment experienced by patients with BD. Not surprisingly, QOL in populations with BD appears to fall far below that observed in general population samples. For example, one study using the medical outcome survey (MOS) SF-3623—the most widely used HRQOL measure in the BD population to date—compared scores of patients with BD (N = 44) with previously reported norms for a general population sample (N = 2474).24 The SF-36 contains 8 subscales that assess physical functioning, social functioning, role limitations (physical), role limitations (emotional), pain, mental health, general health, and vitality. The results of the study indicated that HRQOL was significantly compromised in patients with BD in all SF-36 domains except physical functioning as compared with the general population. While the study provided a useful initial comparison, its findings must be interpreted with caution because of the disparate sample sizes and the use of previously published norms for the HRQOL instrument.
More recent data are provided by Yatham and colleagues,25 who reported on SF-36 scores in a large sample of patients with BD type I (BDI) (N = 920) who either were currently depressed or had experienced a recent episode of depression. Scores were significantly lower across all scale domains in the group of patients with BD than in the general population in the United States, with the patients with BD scoring markedly lower in the mental health, vitality, social functioning, and role emotional domains.
A number of studies have investigated HRQOL in BD compared with other psychiatric conditions. One study from the Netherlands compared SF-36 scores in patients with BD (N = 136) with scores found in patients with a variety of other psychiatric disorders.26 Participants with BD showed significantly more impairment in most SF-36 domains compared with other participants. For example, in the domain of mental health, participants with BDI experienced significantly lower scores (62.3) than people with mood (75.2), anxiety (74.0), substance use (80.2), or no psychiatric disorders (85.8).
In the study by Yatham and colleagues,25 the SF-36 scores in their sample of patients with BD were compared with scores reported in 7 large studies of HRQOL in patients with unipolar depression. Scores on 4 domains (general health, social functioning, role-physical, and role-emotional) were consistently lower in the group with BDI than in the group with unipolar depression; however, the patients with unipolar depression tended to exhibit higher scores in the bodily pain domain.
Although hypomanic symptoms are used to distinguish BD from unipolar depression in the current DSM classification, much of the morbidity and mortality in BD appears to be a consequence of the depressive phase of the disorder, rather than the defining hypomanic or manic phases. Among a sample of 129 patients, those who experienced acute depressive or mixed depressive episodes were at significantly higher risk for suicide, panic disorder, and psychosis than those patients who experienced purely manic episodes.27
There is growing evidence that the deleterious impact of depressive episodes and subsyndromal depressive symptoms in BD extends to QOL and functioning.28-31 Altshuler and colleagues32 found that subthreshold depressive symptoms of BD were significantly predictive of impaired role functioning—specifically, impairment in work, home functioning, and relationships. Indeed, in this sample of 759 patients, odds of experiencing significant impairment in role functioning among patients with subthreshold depressive symptoms were 3 to 6 times greater than for those who were not depressed. Recent findings from the ongoing multicenter STEP-BD trial funded by the NIMH underscore the relationship between depressive symptoms and QOL in BD.33 By comparing the baseline clinical states of the first 2000 participants enrolled in the STEP-BD, Zhang and colleagues8 demonstrated that depressive symptoms were strongly associated with poorer emotional QOL (as measured by the SF-36 mental health subscale), even after relevant confounding variables were controlled for.
Growing evidence for the marked association between depressive symptoms and lowered QOL in BDI is clinically significant, given that depressive symptoms predominate over manic symptoms in patients with BDI and particularly those with BDII.1,34 A large proportion of the QOL challenge of BD may therefore be attributable to depression, consistent with some evidence that QOL scores may be lower in patients with BDII in comparison to patients with BDI.35
The lack of a disorder-specific QOL scale is a limitation of the existing quantitative literature on QOL in BD. Although key aspects of QOL in BD are captured in generic QOL and HRQOL instruments, some of the disorder's unique features (eg, financial indiscretion and hypersexuality when hypomanic) demand specific measurements.36 For this reason, our group has undertaken a program of research to develop a disorder-specific scale for BD (QOL.BD).37,38