We studied IPT as an acute and a maintenance treatment for women with recurrent depression. Our results lead to three conclusions: 1) when IPT alone is effective in bringing about a remission of symptoms, it is also effective as a maintenance treatment; 2) in the maintenance phase, IPT delivered at weekly or twice-monthly intervals is no more effective in maintaining remission than IPT delivered on a monthly basis; and 3) when IPT alone is not effective in the acute treatment phase, it is generally not effective in maintaining remission. Thus, for women who require combined treatment to achieve remission, IPT alone cannot be recommended as a maintenance treatment.
Among participants who remitted with IPT alone during acute treatment and remained in the trial, we observed a recurrence rate of only 26% over a 24-month period of maintenance treatment with IPT alone. This rate is among the lowest observed to date in maintenance treatment studies involving patients with established histories of recurrence (4
). Furthermore, those who remained in the trial for the full 2 years were generally in complete remission throughout that period (mean HAM-D score over 2 years=3.05 [SD=1.81]). In our previous maintenance study (10
), in which patients were treated acutely with a combination of pharmacotherapy and IPT, only those who received an antidepressant in the maintenance phase approached this level of prophylaxis. However, in that trial, we noted that a subset of patients treated with maintenance IPT alone achieved a high level of protection. This subset was characterized by a course of maintenance IPT that was consistently focused on the interpersonal themes that are central to IPT (25
). Among those who achieve remission with IPT alone, perhaps one characteristic of patient/therapist dyads is their ability (either inherent in the dyad or learned during acute treatment) to remain focused on interpersonal themes during the therapy sessions. This hypothesis is supported by analyses (26
) demonstrating that subjects who did not do well in the acute phase of this trial tended to have higher levels of somatic anxiety symptoms, somatic complaints, and preoccupation with somatic changes—features likely to have interfered with their ability to focus on interpersonal themes during their therapy sessions. Thus, the ability to achieve stable remission with IPT alone may have selected the subpopulation uniquely able to remain focused on interpersonal themes and benefit from this specific treatment.
To our surprise, we found no difference in prophylactic efficacy among the three frequencies of maintenance IPT we studied. We did, however, observe clear differences in the risk of recurrence in those participants who achieved remission with IPT alone as compared with those who required the addition of pharmacotherapy. Indeed, the subgroup that required the addition of an SSRI to achieve a sustained remission had a markedly different clinical course throughout the trial. Although the remission rate for the group that received psychotherapy plus an SSRI was reasonably good, the continuation treatment phase was not benign for these subjects; 29% experienced a relapse, including 15% who relapsed while receiving combined treatment. Four additional relapses occurred in the transition to maintenance treatment with IPT alone, either during the process of medication discontinuation or shortly thereafter. This points to the potential difficulty of discontinuing medication after successful resolution of acute symptoms in patients who require the addition of pharmacotherapy to ongoing psychotherapy. At the time the study was conducted, and considering the strong preference of many women in their childbearing years for nonpharmacologic treatment, the attempt to withdraw medication after 5 months of stable remission seemed reasonable; however, this report now adds to the accumulating data supporting the necessity of pharmacologic maintenance treatment in individuals who require pharmacotherapy to achieve remission. Given the small number of participants in this subgroup who were able to enter the maintenance phase and the low likelihood that many clinicians today would elect to provide nonpharmacologic maintenance treatment alone to women who needed combination treatment to achieve remission, generalization from this subsample about the value of various frequencies of IPT is probably not meaningful.
Although no statistically significant differences were found in baseline HAM-D scores or number of previous episodes, it seems likely that participants in the group needing sequential treatment had some biological difference from the other group that is not reflected in the measures we employed. As we reported earlier (26
), subjects whose depression was complicated by panic-like symptoms or a panic spectrum disorder had a more problematic acute treatment course; however, these features are not captured by total scores on traditional measures of depression severity.
A major limitation of the design of this study is that it did not include a no-treatment comparison condition in the maintenance phase. Having observed high rates of recurrence among subjects assigned to brief “medication clinic” visits with placebo in our original maintenance trials, we felt a no-treatment control condition would not be ethical in this study.
The literature on maintenance treatment increasingly indicates that if a patient gets well (not merely better, but well) on any given treatment, the prudent maintenance strategy is to continue that treatment. For medication, it seems that this needs to be done at the full dose that was used to achieve remission. For psychotherapy, in contrast, the continuation and maintenance studies completed to date suggest that relatively infrequent contact, in the form of either booster sessions or monthly treatment sessions, may be sufficient to protect the majority of individuals who are able to achieve remission with psychotherapy alone in the subsequent 1 to 2 years. Thus, session frequency may represent a limited analogy to the concept of medication dose. Other factors, such as fidelity to the therapeutic model and therapeutic intensity, which are not captured by visit frequency, may be more important for protection against recurrence.
While it is clear in retrospect that a subgroup of the women we studied was well served in both acute and maintenance treatment by a depression-specific psychotherapy, none of the traditional measures of severity or other parameters of illness distinguished that subgroup from those who required the combination therapy to achieve remission and, in many cases, to maintain that remission. The field clearly needs new ways of distinguishing the various phenotypes of unipolar disorder for which treatment requirements differ. This need is likely to be met only if we develop new and more subtle means of characterizing patients than our current measures of depression severity provide.