Department of Psychology, University of Pennsylvania, Philadelphia, Pennsylvania
Department of Psychiatry, Vanderbilt University, Nashville, Tennessee
Department of Mathematics and Applied Statistics, West Chester University, West Chester, Pennsylvania
Department of Psychiatry, University of Pennsylvania, Philadelphia, Pennsylvania
Department of Psychology, Vanderbilt University, Nashville, Tennessee, USA
Correspondence: Robert J. DeRubeis, Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104–6196, USA. Email: derubeis{at}psych.upenn.edu
R.C.S has received grant support from GlaxoSmithKline Pharmaceuticals. Funding detailed in Acknowledgements.
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There is conflicting evidence about comorbid personality pathology in depression treatments.
Aims
To test the effects of antidepressant drugs and cognitive therapy in people with depression distinguished by the presence or absence of personality disorder.
Method
Random assignment of 180 out-patients with depression to 16 weeks of antidepressant medication or cognitive therapy. Random assignment of medication responders to continued medication or placebo, and comparison with cognitive therapy responders over a 12-month period.
Results
Personality disorder status led to differential response at 16 weeks; 66% v. 44% (antidepressants v. cognitive therapy respectively) for people with personality disorder, and 49% v. 70% (antidepressants v. cognitive therapy respectively) for people without personality disorder. For people with personality disorder, sustained response rates over the 12-month follow-up were nearly identical (38%) in the prior cognitive therapy and continuation-medication treatment arms. People with personality disorder withdrawn from medication evidenced the lowest sustained response rate (6%). Despite the poor response of people with personality disorder to cognitive therapy, nearly all those who did respond sustained their response.
Conclusions
Comorbid personality disorder was associated with differential initial response rates and sustained response rates for two well-validated treatments for depression.
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We present data drawn from a multi-site randomised controlled trial comparing cognitive therapy and paroxetine for individuals diagnosed with moderate-to-severe depression.7,8 We focus on whether the presence of comorbid personality disorder predicts differential response to cognitive therapy and pharmacotherapy, and we explore the effect of comorbid personality disorder on relapse once treatment is terminated.
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Treatment
Participants were randomly assigned to receive cognitive therapy
(n=60), antidepressant treatment with paroxetine (n=120) or
pill placebo (n=60) (Fig.
1). After 8 weeks of the 16-week acute treatment phase, the
placebo arm was terminated and individuals who had been receiving placebo were
offered antidepressant treatment at no cost. Because 8 weeks of treatment is
generally not regarded as sufficient to treat people with comorbid personality
disorders, comparisons that include the placebo group were not included in the
analyses below.
![]() View larger version (25K): [in a new window] [as a PowerPoint slide] |
Fig. 1 Flow diagram of participants through the study. ADM, antidepressant
medications; CT, cognitive therapy; cADM, continuation antidepressant
medications during the continuation phase; cP-P, placebo during the
continuation phase.
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The criterion for response at 16 weeks was an HRSD score of 12 or lower. In order to limit the effect of transient mood fluctuations on the response designation, additional constraints required participants to have scored 14 or less at week 14, or 12 or less at weeks 10 and 12. Individuals who scored higher than 12 at week 16 were still considered `responders' if they had scored 12 or below at weeks 12 and 14, and again scored 12 or below at an additional evaluation at 18 weeks. Response at 16 weeks also required the completion of acute treatment.
Of the 180 people assigned to antidepressants or cognitive therapy, 104 people met the response criteria at 16 weeks and were entered into the 12-month continuation phase of the study. Half of the responders from the antidepressant group (n=35) were randomly assigned to be withdrawn from medication onto pill placebo (continuation placebo) while the other half (n=34) were continued on medication (continuation medication) throughout the 1-year continuation phase. In the cognitive therapy condition, regular therapeutic contact ceased at the end of the acute phase of treatment. Treatment responders (n=35) could use up to three 1-hour booster sessions throughout the 1-year continuation phase. When individuals on antidepressants were randomised to continuation placebo or continuation medication at the beginning of the continuation phase, the process was triple blind – participants, pharmacotherapists and evaluators did not know which individuals were receiving active medication.
Outcome measures
The primary outcome measure was the 17-item version of the HRSD. During the
acute phase, assessments with evaluators masked to treatment condition were
held weekly for the first 4 weeks and biweekly from week 6 to week 16. During
the continuation phase, assessments were conducted during each of the first 2
weeks, biweekly through to the end of the second month, and monthly
thereafter. Relapse was defined as a score of 14 or greater on the HRSD during
two consecutive weeks (ad hoc assessments were scheduled as needed to
confirm this temporal component). If a person experienced a worsening of
symptoms in the interval between assessments, the timing of relapse was
ascertained using the Longitudinal Interval Follow-up
Evaluation,13
conducted at the next assessment. Of the 45 participants who were judged to
have relapsed, 11 were ascertained using this instrument.
Statistical analyses
The primary statistical analyses examined whether there were differences in
efficacy between the two treatments as a function of personality disorder
status, by examining:
Data from all participants randomised to treatment were included in all three sets of (intent-to-treat) analyses. In the case of attrition, all data collected up to the date of attrition were included. In each analysis, the treatment x personality disorder status interaction term was of primary interest.
For the acute phase data, Cochran–Mantel–Haenszel tests were
used to assess differential response/non-response as a function of treatment
and personality disorder status, stratified across the two
sites.14 Odds
ratios (ORs), confidence interval (CI) bands and interaction effects were
assessed using a logistic regression model based on the likelihood ratio
2
statistic.15
Continuous data were examined with multiple regression techniques using a last
observation carried forward approach and with hierarchical linear modeling.
The hierarchical linear modeling approach adjusts for repeated measures with
nested random
effects.16,17
Using this approach, each person's growth curve and true HRSD score at the end
of treatment can be estimated from a collection of individual-specific
parameters.18 For
all hierarchical linear modeling analyses reported, an unstructured covariance
structure was assumed in order to model random intercepts and slopes. Two
baseline scores were obtained for all participants, allowing for a full
intent-to-treat analysis while at the same time covarying for each person's
initial baseline depression severity score. All models were performed using
SAS Version 9.0 for Windows, PROC MIXED for hierarchical linear modelling
analyses, PROC GLM for multiple regression analyses, PROC FREQ for
Cochran–Mantel–Haenszel tests, and PROC GENMOD for Logistic
Regression (SAS Institute Inc, Cary, North Carolina, USA).
The Cox proportional hazards model was used to estimate attrition rates and relapse rates.19 Because a differential response rate for people with and without personality disorder emerged between the two treatments (see below), the Cox proportional hazards technique is inappropriate on its own to estimate survival rates during the continuation phase. Any indication of differential relapse might be an artifact of a differential sieve through which individuals who would be at greatest relapse risk already had failed to respond to a particular treatment,20 and therefore did not enter the continuation phase. To address this concern, estimated survival curves from Cox proportional hazards regression models were weighted by the proportion of people who responded in each treatment arm. This procedure estimates the percentage of people who both responded to treatment and maintained that response throughout the 1-year continuation phase. In the original publication, four possibly confounding covariates (dysthymia, atypical depression, number of prior episodes and gender) were entered in the survival analyses;8 these were performed using the present models as well. These models were performed using the SAS procedure, PROC PHREG.
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21=0.32,
P=0.57), a statistically non-significant trend-level personality
disorder status x treatment interaction did emerge
(
21=2.72, P<0.10). This effect was
driven in large part by the fact that the attrition rate was lower for people
with personality disorder (12%) than for people without personality disorder
(21%) in the antidepressant arm, and lower for people without personality
disorder (12%) than for people with personality disorder (22%) in the
cognitive therapy arm.
Outcome of acute treatment
Categorical response analyses
There was a significant interaction between treatment and personality
disorder status in acute treatment response
(
21=6.77, P=0.009). As displayed by the
narrow bars in Fig. 2, people
with personality disorder showed a non-significant trend in favour of
antidepressants; 66% (95% CI 54–78) met response criteria compared with
44% (95% CI 25–63) in the cognitive therapy arm
(Cochran–Mantel–Haenszel
21=3.42,
P=0.06; OR=2.42, 95% CI 0.96–6.28). The reverse pattern was
observed, as a non-significant trend, for people without personality disorder,
with 70% (95% CI 54–86) meeting response criteria in the cognitive
therapy arm, compared with 49% (95% CI 36–62) in the antidepressant arm
(Cochran–Mantel–Haenszel
21=3.20,
P=0.07; OR=2.28, 95% CI 0.94–5.81). The tests of the main
effects of treatment, personality disorder status and the three-way site
x treatment x personality disorder status interaction were
non-significant (all
2s<0.43, all Ps>0.51).
![]() View larger version (34K): [in a new window] [as a PowerPoint slide] |
Fig. 2 The percentage of individuals in each treatment arm meeting response and
sustained response criteria. ADM, antidepressant medication; CT, cognitive
therapy. The narrow bars display the proportion of people who met response
criteria in the two treatments (antidepressants and cognitive therapy) at the
end of the 16-week acute phase. The wide bars represent the estimated
proportion of individuals who survived the 12-month follow-up period without a
relapse. Bars on the left half of the figure represent individuals diagnosed
with a comorbid personality disorder; bars on the right represent individuals
who did not have a comorbid Axis-II diagnosis.
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Potential confounds
To address the possibility that people with personality disorder differed
from those without personality pathology in other important ways, we examined
eight history of illness variables, two depression subtype variables, four
composite Axis I comorbidity variables, seven demographic variables and, for
people in the antidepressant arm, dosage and augmentation, to determine
whether people with and without personality disorder differed at the
P<0.10 level. As shown in online table DS2, nine of these
variables differed between the two groups. All nine variables were entered
simultaneously into each of the models reported above. For the model
predicting categorical response, as well as the hierarchical linear model
predicting end of treatment HRSD scores, the personality disorder status
x treatment interaction remained significant even with the simultaneous
addition of all nine variables (
21=5.59,
P=0.02 for the categorical analysis; F1,164=4.13,
P=0.04 for the hierarchical linear model). In the last observation
carried forward analysis, the personality disorder status x treatment
interaction became a non-significant trend (F1,164=3.54,
P=0.06).
Individual personality disorder diagnoses
The results reported thus far were achieved by comparing all participants
with at least one personality disorder diagnosis with participants with no
personality disorder diagnosis. In order to better determine what was driving
the observed effects, we conducted exploratory analyses examining the
relations for individual personality disorders. The strongest pattern occurred
for people diagnosed with personality disorder not otherwise specified (NOS),
wherein 12 of 16 people (75%) responded to antidepressants and 3 of 9 (33%)
responded to cognitive therapy (OR=6.09, 95% CI 1.09–42.87, in favour of
antidepressants over cognitive therapy). In order to examine this effect
further, we assigned individuals diagnosed with personality disorder NOS to
the personality disorder cluster in which their highest concentration of
symptoms was observed. For example, a broad-band Cluster C category was formed
by combining individuals with personality disorder NOS for whom the highest
concentration of symptoms fell in Cluster C with those individuals who
actually received a Cluster C diagnosis. The effect of personality disorder
status was the strongest for individuals in the broad-band Cluster B category.
Of the 16 people in the broad-band Cluster B grouping, 6 of the 9 individuals
treated with antidepressants responded, whereas only 1 of 7 individuals being
treated with cognitive therapy responded (OR=15.03, 95% CI 1.36–515.92).
For people in the broad-band Cluster C group, 32 of 47 (68%) responded to
antidepressants, whereas 10 of 19 (53%) responded to cognitive therapy
(OR=1.97, 95% CI 0.65–5.98). For those in the broad-band Cluster A
group, 2 of 4 responded to cognitive therapy v. 1 of 4 who responded
to antidepressants (OR=3.28, 95% CI 0.16–137.50).
Sustained response through the 12-month continuation phase
For the 12-month continuation phase, the survival rates of the three
treatment arms (prior cognitive therapy, continuation placebo and continuation
medication) were estimated for individuals with and without personality
disorder. Sustained response estimates for each group were then calculated by
computing the product of these survival estimates and the group's treatment
response rate (e.g. for people with personality disorder who had received
antidepressant treatment, survival estimates for both the continuation
medication and continuation placebo arms were multiplied by the percentage of
people with personality disorder who responded to acute antidepressant
treatment). Analysis of these estimates revealed a significant treatment
x personality disorder status interaction in the percentage of people
who showed a sustained response through the end of the 12 months
(
22=6.13, P=0.047). For people with
personality disorder, a significant main effect of treatment emerged
(
22=11.94, P=0.003). The wide bars in
Fig. 2 show that despite the
fact that a higher percentage of people with personality disorder responded to
treatment (and hence entered the continuation phase) in the antidepressant arm
(66%) compared with the cognitive therapy arm (44%), an estimated 38% of
patients (95% CI 20–56) initially randomised to cognitive therapy
evidenced sustained response. With a higher relapse rate in the continuation
medication arm, a nearly identical estimate of the proportion of people with
sustained response was obtained in this group (38% (95% CI 21–55)).
People with personality disorder who had previously received antidepressants
but were withdrawn onto continuation placebo tended to relapse at an extremely
high rate. Only 6% of these people (95% CI –3 to 15) exhibited sustained
response. Specific contrasts revealed that, for people with personality
disorder, prior cognitive therapy and continuation medication were each
superior to continuation placebo on the sustained response variable
(
21=9.80, P=0.002 for continuation
medication v. continuation placebo;
21=9.15, P=0.003 for prior cognitive
therapy v. continuation placebo). There was no difference in
estimated sustained response rates between prior cognitive therapy and
continuation medication for this group (
21=0.002,
P=0.97).
For people without personality disorder, the main effect of treatment was
not significant in the analysis of sustained response
(
21=4.54, P=0.103).
Figure 2 shows that for people
initially randomised to receive cognitive therapy, 43% (95% CI 26–60)
exhibited sustained response compared with 23% (95% CI 8–38) for those
initially randomised to receive antidepressant treatment who were then
assigned to continuation placebo, and 21% (95% CI 7–35) for those who
were assigned to antidepressant treatment and then were assigned to
continuation medication.
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Antidepressants, on the other hand, worked particularly well to reduce depressive symptoms for patients diagnosed with comorbid personality pathology. Although individuals with and without personality disorder differed in several respects, including the incidence of comorbid anxiety disorders, none of these factors accounted statistically for the differential treatment effects. Results from the continuation phase of the study further support the conclusion that antidepressants had potent effects in this group in that nearly all of the people with personality disorder who were withdrawn from medication relapsed. For people with depression who did not have diagnosed personality pathology, there was a suggestion in the data that cognitive therapy was particularly effective at reducing depressive symptoms, relative to antidepressants.
Limitations
The pattern of findings in regard to acute treatment response was
consistent across the three different analytical methods, and the test of
significance for the interaction of interest was met in all three. However, in
the analysis that employed hierarchical linear modelling, the interaction of
interest was significant only in the prediction of 16-week scores and not in
the prediction of symptom change over time. This inconsistency may have arisen
because of the fact that hierarchical linear modelling analyses can lead to
misleading estimates of improvement rates in data-sets containing non-random
attrition.22,23
Consistent with the observation that people with personality disorder assigned
to cognitive therapy and people without personality disorder assigned to
antidepressants fared more poorly than the other two groups, individuals
within these groups also tended to have higher rates of attrition. This is
another indication that antidepressants were better-suited to people with
personality disorder in this trial and that cognitive therapy was better
suited to people without personality disorder. In addition, between-treatment
differences in outcome within the subgroups of individuals with and without
personality disorder were at the level of non-significant trends. Since these
tests were associated with relatively low power, these comparisons will be
most useful to the field as constituents of future meta-analyses that will
combine the current findings with attempts to replicate these results.
A second limitation involves the duration of the active treatments. The differences between cognitive therapy and antidepressants in relation to personality disorder status may have depended, in part, on the fact that the treatments were brief, relative to the durations recommended for treating people with depression who have comorbid personality disorder. Given more time, cognitive therapy might have been as effective as antidepressants for people with personality disorders, and antidepressants might have been as effective as cognitive therapy for people without personality disorders. Nevertheless, short-term treatment did lead to response percentages of up to two-thirds of people with personality disorder in the antidepressant arm, as well as for people without personality disorder in cognitive therapy.
Third, prospective participants with diagnosed schizotypal, antisocial or borderline personality disorders were excluded from the trial. Thus, these results do not, strictly speaking, generalise to the population that includes people with these comorbidities. However, only 5% of otherwise eligible participants were excluded because they received one of these diagnoses, and all but one of these individuals was excluded because of a Cluster B diagnosis. People in this trial whose highest concentration of personality disorder symptoms occurred in Cluster B showed a particularly strong response to antidepressants relative to cognitive therapy. This suggests that the pattern we observed might be even stronger in a sample that includes all Axis II comorbidities.
Future directions
Because the primary medication used in this study, paroxetine, has
demonstrated efficacy in treating depression with comorbid anxiety disorders,
it might have been expected that the antidepressants' relative efficacy for
people with personality disorder was due to its superiority for patients with
Cluster C personality
disorders.24
However, the numerical advantage for antidepressants was strongest for people
with Cluster B personality pathology. One possible explanation for this result
is suggested by research demonstrating that people with Cluster B personality
disorders display deficits in cortical regions thought to underlie the
regulation of emotion and the inhibition of impulsive
aggression,25 and
from studies that demonstrate that selective serotonin reuptake inhibitors can
reduce mood lability, anger and impulsive behaviour in humans and
animals.26–28
Future studies might attempt to further investigate these mechanisms in people
with depression and this type of personality pathology. In addition, the
surprisingly high rate of relapse among people with personality disorder
withdrawn from medication should be examined in future research, as the
mechanism driving this effect is currently unclear.
Clinical implications
The pattern of results from this study suggests possible prescriptive
recommendations regarding short-term treatment for people with
moderate-to-severe depression as a function of comorbid personality pathology.
Evidence from this study, consistent with findings from other investigations,
suggests that for people with depression with a comorbid personality disorder,
paroxetine treatment is more likely than cognitive therapy to alleviate their
depressive symptoms in the short term. Because of a higher relapse rate for
people receiving continuation medication, short-term cognitive therapy may
produce rates of sustained response roughly equivalent to those achieved with
sustained antidepressants, provided that booster sessions are given to
individuals receiving cognitive therapy. Given the relatively low relapse rate
among people with personality disorder who responded to cognitive therapy, the
combination of antidepressants and cognitive therapy might be especially
valuable for these people. Individuals without a personality disorder
diagnosis fared better during acute treatment and exhibited a higher sustained
response rate while receiving cognitive therapy, compared with
antidepressants. Indeed, these people appeared to be equally susceptible to
relapse following acute treatment with antidepressants regardless of whether
they were continued on medication or withdrawn onto placebo. This pattern, if
replicated, could lead to the consideration of cognitive therapy as a
first-line treatment for people with depression who do not have a personality
disorder.
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