In the present analysis we aimed to determine (a) the prevalence of specific residual symptoms in patients who responded to acute phase CT and (b) if any specific residual symptoms were risk factors for increased relapse/recurrence over two year follow-up. A high percentage of patients continued to endorse several residual symptoms after response to acute phase cognitive therapy, which was largely consistent with previous research (e.g., Opdyke et al., 1996
; Paykel et al., 1999
). Adult responders to acute phase CT continued to report depressed mood, psychic anxiety, somatic anxiety, insomnia (specifically middle insomnia), feelings of guilt, anergia, and loss of libido in large percentages. Several of these specific residual symptoms were risk factors for relapse/recurrence, including decreased agitation, and increased psychological anxiety, loss of appetite, loss of libido, and hypochondriasis, after controlling for C-CT, age at onset, and their interaction.
These results indicate that specific residual symptoms may be a reasonable target for intervention if relapse and recurrence are to be prevented. Some of studies have examined treating post-medication residual symptoms with CT (Fava et al., 1994
; Paykel et al., 1999
), with positive results. However, those CT interventions were “generic” and did not appear target specific
depressive symptoms, which were likely to persist and predict relapse/recurrence. In the parent study (Jarrett et al. 2001
), C-CT reduced relapse over 8 months, which we controlled for, but left it to the patient and therapist to determine how much, if at all, to focus on specific residual symptoms. To increase the impact of CT, targeting the specific symptoms known to forecast relapse/recurrence may reduce such risk.
There was one counterintuitive result. Decreased agitation predicted increased relapse/recurrence. In the current sample, 94% of responders received a score of 0 (“absent”) on the HRSD agitation item, and 6% received a score of 1 meaning “fidgety.” It is unclear why responders who were not fidgety relapsed/recurred more. One could hypothesize that some responders who were not fidgety had lower activation or increased lethargy (i.e., as seen with psychomotor retardation), although sampling error should be ruled out, as well. Consequently, our finding regarding agitation should be interpreted with caution until it has been replicated.
If the current pattern of results can be replicated, next steps would include exploring why some residual symptoms present greater risk for relapse/recurrence than do other symptoms. For example, the symptom predictors identified in the current analyses may have a greater impact on psychosocial functioning that often deteriorates before relapse and recurrence (Vittengl et al., 2009
), or these symptoms possibly are stronger markers of “core” deficits in unipolar depression (Gullion and Rush, 1998
). Understanding such mechanisms would inform development of interventions to decrease risk for relapse/recurrence.
While the results of this study shed light on the nature of residual symptoms following response to acute phase CT, there are limitations which need to be considered when interpreting the results and looking at clinical implications. The findings were based on a limited sample of 84 adults who responded to acute phase CT. This relatively small number of participants limits the power and generalizability of the findings. The study sample was also restricted in terms of gender, ethnicity, region, mean education level and employed highly competent therapists.
Future studies may want to examine self-report measures of depression in addition to a clinician-rated report, such as the Inventory of Depressive Symptomology-Clinician Rated (IDS-CR) and Inventory of Depressive Symptomology-Self Report (IDS-SR) (Rush et al., 1986
). Limiting the current evaluation of symptoms to a clinician rating may have obscured full description of residual symptoms; patients may have different perspectives on the change in their symptoms than clinicians.
Some patients with recurrent MDD have such a high risk for further episodes that full elimination of continuation or maintenance treatment may not be a reasonable objective, until the field discovers a cure for depressive disorders. Patients with recurrent MDD require ongoing clinical monitoring with continuation and maintenance therapies (CT or otherwise) adapted to their particular symptom status and to their early indications of imminent risk of relapse/recurrence. Periodic CT focused on maintaining and extending specific skills acquired during acute CT may be particularly effective for certain patients, not only for reducing the risk of relapse/recurrence, but also for maintaining their gains in psychosocial functioning (Vittengl et al., 2004
Researchers informed by the current results might test clinically and theoretically interesting potential moderators of residual symptoms' impact on relapse/recurrence (e.g., patients' level of skill acquired during A-CT, personality trait dimensions relevant to depression, age of onset of MDD, continuation treatment type). Future research testing moderators may require larger samples because of the low base rates of residual symptoms among patients who respond to A-CT (e.g., median = 17% for HRSD items in the current sample). When residual symptoms are fully understood, clinicians can begin to develop treatment strategies to target these symptoms. Ideally, the goal would be to make the acute phase of treatment more effective so that a continuation or maintenance phase can be shorter. This analysis identifies symptom targets for both acute and continuation treatment toward the goal of reducing relapse rates among those living with recurrent depression by reducing residual symptoms.