Although we observed similar overall rates of MDD remission in this 2-year prospective study for men (74.5%) and women (72.4%), our findings suggest that PDs significantly predict a pattern of slowed time to remission from MDD. Participants with MDD who had certain forms of coexisting PD psychopathology (STPD, BPD, or AVPD) as their primary PD diagnoses had a significantly longer time to remission from MDD than did patients with MDD without any PD. These patterns of slowed remission from MDD were similar for women and men. These forms of PDs emerged as robust predictors of slowed remission from MDD even when controlling for other potential negative prognostic predictors selected from the depression literature.
Our overall remission rate for MDD is comparable with that reported by the NIMH-CDS (Keller et al., 1982
) for the same time frame on the basis of the same assessment methodology (LIFE) and analytic procedures (life table analyses), albeit with slightly different diagnostic systems. An interesting finding was that the MDD remission rates for patients grouped by the presence of PDs in our study bear some resemblance to the remission rates reported by Keller et al. (1982)
for MDD patients grouped by dysthymia (with superimposed illness [59%] versus without superimposed illness [79%]) over 24 months, as do the time to remission data (survival curves).
Our study considered a number of predictors, including gender, ethnicity, and treatment, along with clinical predictors from the MDD literature (e.g., dysthymia, Axis I comorbidity, whether the MDD had a recurrent pattern, and age of onset of MDD). We found that certain forms of PD comorbidity contributed significantly to slowing remission from MDD but that none of the other variables we covaried for potential confounding were found to have a statistically significant effect on time to remission from MDD. Previous studies have reported associations among PDs, dysthymia, and certain characteristics of MDD such as earlier onset and recurrence (Klein et al., 1999
). Our analyses suggest that specific forms of PD psychopathology (STPD, BPD, and AVPD)— but not necessarily other forms of PD (i.e., OCPD) or just a generic total number of PD diagnoses— emerge as significant predictors of slower MDD remission.
We found that certain forms of PD psychopathology predict a similar pattern of slower remission from MDD for both men and women. The presence of STPD, BPD, and AVPD, along with their associated additional forms of personality dysfunction, significantly and substantially delay the time to remission from MDD relative to the time to remission observed for patients with MDD without any coexisting PD. The OCPD group, which reduced the MDD remission rate by a factor of roughly 1.6 –1.0, did not have a statistically significant effect, which reflects a combination of lower power (smaller sample) coupled with the lower effect size observed for the other PD study groups. The presence of additional PDs per se does not appear to contribute to further delaying the time to remission.
Much has been written about possible complex biopsychosocial factors that might account for gender differences in the frequency, expression, and natural history of MDD (Hankin & Abramson, 1999
). Our findings suggest that the presence of certain severe forms of PD psychopathology might override usual gender differences. It is worth noting that although time to remission from MDD did not differ by gender, gender rates were different for certain PDs (e.g., a higher proportion of men had STPD and a higher proportion of women had BPD), suggesting that there might be gender differences in risk for certain types of PD psychopathology and hence in time to remission from MDD.
Hankin and Abramson (1999
), in their elaborated developmental cognitive vulnerability-transactional stress model, detailed gender differences in personality and associated cognitive vulnerabilities that can interact with negative affect and/or negative events (particularly interpersonal events) and lead to increases in depression and to further negative events that continue to fuel the distress. Our findings suggest that the presence of these personality and cognitive vulnerabilities can greatly and negatively impact both men and women. Of course, the finding that such vulnerabilities can affect both men and women does not necessarily mean that they are driven by the same mechanisms.
We briefly note method limitations as a context for our findings. Interviews conducted during this 2-year period were nonblind to baseline status. Although it is possible that this method may have contributed a bias, the use of the same interviewer provides the advantage of repeated contacts with the participant. This may increase the validity of the MDD ratings on the LIFE and diminish the error due to rater variance.
A second limitation of naturalistic longitudinal studies of clinically ascertained participants is the potential for confounding by treatment. In our initial study of treatment use (Bender et al., 2001
), MDD patients without PDs used significantly less treatment than patients with PD, and the patients with the more severe forms of PDs (including those with more PDs) reported receiving the most treatment. Such findings suggest that the amount of treatment received is driven by the severity of the disorder, which is a typical finding in naturalistic studies (Cochran, 1983
). Consistent with this, in the present study, our prospective analyses revealed that (a) MDD patients with more PDs (and slower time to remission) were more likely to receive treatment than those without PD and (b) a treatment intensity composite variable entered into the omnibus multiple regression analysis did not have a statistically significant effect on time to remission from MDD. We note, however, that this study was designed to address the question of the course of MDD in patients in real-world clinical settings. Our study was not designed to address the important, but distinct, questions of the untreated course of MDD or of treatment outcome in MDD (Mulder, 2002
) with experimentally controlled treatment.
Another issue concerns the definition of remission
from MDD as 8 consecutive weeks with PSR ratings no higher than 2 (reflecting minimal or no symptoms). This definition follows the NIMH-CDS (Keller et al., 1982
; Solomon et al., 1997
) and therefore allows for direct comparison with that prospective longitudinal study. Researchers in the field of MDD have debated and struggled with the important issues of how to best define terms such as remission (Frank et al., 1991
). Further research making use of longitudinal data sets might improve on these definitions. On the basis of present knowledge, however, this definition appears to have some merits. Whereas the duration criterion (8 consecutive weeks) might seem brief, the consecutive requirement at 2 or fewer PSRs is strict. In support of this argument, we note the impressive longitudinal studies that have documented that subthreshold depression (i.e., below threshold for MDD but falling about the remission criteria) is clinically quite meaningful as demonstrated by its chronic course and high levels of associated impairment (Judd, Akiskal, et al., 2000
; Judd et al., 1998
; Judd, Paulus, et al., 2000
In summary, we found that the presence of certain PDs predicts a pattern of slowed remission from MDD. Patients with MDD who had coexisting STPD, BPD, or AVPD as primary PD diagnoses had a significantly slower time to remission from MDD than did patients with MDD without any PD. These PDs emerged as robust predictors of slowed remission from MDD even when controlling for other negative prognostic predictors. In this ongoing CLPS study, future analyses will attempt to delineate factors that might influence the timing of changes—such as relapses (Ilardi et al., 1997
) and associated changes (e.g., life events, treatment, psychosocial functioning)—and how these factors contribute to the longer-term course of depression.