Habituation of distress during exposure and its relationship to treatment outcome in post-traumatic stress disorder and prolonged grief disorder

ABSTRACT

Background: Reliving distressing memories is a core component of treatments for post-traumatic stress disorder (PTSD) and prolonged grief disorder (PGD). There is little understanding of how reliving these memories functions in the treatment of these disorders.

Objective: This study investigated whether reliving functions comparably in the treatment of PTSD and PGD, and whether it is comparably related to treatment outcome.

Method: This study conducted a reanalysis of patients with either PTSD (n = 55) or PGD (n = 45) who underwent treatments that comprised at least four sessions of reliving memories of either their traumatic experience or the loss of the deceased person.

Results: PTSD participants displayed greater habituation of distress across sessions during reliving than PGD participants. Between-session reduction in distress during reliving was associated with symptom remission in PTSD, but this pattern was not observed in PGD.

Conclusion: This pattern of findings indicates that although reliving appears to be a useful strategy for treating both PTSD and PGD, this strategy does not function comparably in the two conditions and may involve distinct mechanisms.

HIGHLIGHTS

• Reliving distressing memories is key to treatment of PTSD and prolonged grief disorder.

• Distress during memory reliving habituated in PTSD treatment more than in treatment of grief.

• Habituation of distress during treatment predicted remission of symptoms in PTSD but not grief.

Antecedentes: Revivir los recuerdos angustiosos es un componente central de los tratamientos del Trastorno por estrés postraumático (TEPT) y trastorno por duelo prolongado (PGD por sus siglas en ingles). Existe poca comprensión de cómo el acto de revivir estos recuerdos funciona en el tratamiento de estos trastornos.

Objetivo: Este estudio investigó si la acción de revivir funciona de manera comparable en el tratamiento del TEPT y del PGD y si están relacionados de manera comparable con los resultados del tratamiento.

Método: Este estudio condujo un nuevo análisis de pacientes con TEPT (n=55) o PGD (n=45) que estuvieron en tratamiento que comprendían al menos cuatro sesiones de revivir los recuerdos de la experiencia traumática o la perdida de sus seres queridos.

Resultados: Los participantes con TEPT mostraron una mayor habituación al malestar (angustia) en las sesiones durante la acción de revivir que los participantes con PGD. La reducción de la angustia entre sesiones durante el acto de revivir se asoció con la remisión de síntomas en el TEPT, pero este patrón no se observó en el PGD.

Conclusión: Este patrón de hallazgos indica que aunque el acto de revivir parece ser una estrategia útil para tratar tanto el TEPT como el PGD, esta estrategia no funciona en forma comparable en las dos condiciones y puede involucrar mecanismos distintos.

简介：重温痛苦的记忆是治疗创伤后应激障碍 (PTSD) 和延长哀伤障碍 (PGD) 的核心组成部分。 对重温这些记忆在治疗这些疾病中的作用知之甚少。

目的：本研究考查了重温在 PTSD 和 PGD 治疗中的作用是否相当，以及它们与治疗结果的相关性是否相当。

方法：本研究对接受了包括至少四疗程重温其创伤经历或丧亲记忆治疗的PTSD患者 (n = 55) 或 PGD患者 (n = 45) 进行了重新分析。

结果：PTSD 参与者在重温过程中表现出比 PGD 参与者更大的痛苦习惯化。 重温期间痛苦减少与 PTSD 症状缓解相关，但在 PGD 中未观察到这种模式。

结论：发现的这种模式表明，虽然重温似乎是治疗 PTSD 和 PGD 的一种有用策略，但这种策略在这两种情况下的作用并不相同，并且可能涉及不同的机制。

KEYWORDS:

• PTSD
• prolonged grief disorder
• prolonged exposure
• habituation
• treatment response

PALABRAS CLAVE:

• TEPT
• trastorno por duelo prolongado
• exposición prolongada
• habituación
• respuesta al tratamiento

关键词:

• 创伤后应激障碍
• 延长哀伤障碍
• 延长暴露
• 习惯化
• 治疗反应

1. Introduction

Reliving a traumatic memory is a major component of many recommended treatments for post-traumatic stress disorder (PTSD), which can be described as trauma-focused cognitive behavioural therapy (TF-CBT). This strategy involves a person recounting their trauma in a detailed and emotionally engaging manner. In its original form in the treatment of PTSD, reliving the trauma memory was based on emotional processing theory (Foa, 2006). This model posits that remission of PTSD involves activating the fear structure that was developed after trauma exposure and integrating corrective information that modifies maladaptive representations and associated emotions. In recent years, reliving distressing memories has also been integrated into the treatment of prolonged grief disorder (PGD), which describes persistent grief reactions that are characterized by ongoing yearning for the deceased and related symptoms (World Health Organization, 2018). Effective treatments for PGD typically include recalling memories of the death in which the person is directed to relive memories involving the death of the deceased (Boelen et al., 2007; Shear et al., 2005; Shear et al., 2016). Highlighting the utility of reliving memories of the death, one study showed that integrating this strategy resulted in greater treatment gains than using other components of this treatment without reliving (Bryant et al., 2014, 2017).

Although there is considerable overlap between conceptualizations and implementations of reliving distressing memories in treatment of PTSD and PGD, there are also important differences. Whereas reliving the trauma memory for PTSD is typically the predominant strategy used throughout therapy and can be repeated for up to 40 min in each session (Foa, 2006), the use of reliving memories of the death in the treatment of PGD usually occurs once in up to four sessions and occurs in the context of a range of other treatment modalities, including cognitive restructuring, fostering future relationships, behavioural activation, and goal setting (Shear et al., 2005). Conceptually, it has been postulated that reliving trauma memories achieves symptom reduction via a number of processes, including habituation to the trauma memory, as defined by a reduction of the distress associated with the memory, extinction learning that these memories are not threatening, integration of corrective information, and a sense of self-mastery (Rothbaum & Schwartz, 2002). The proposed mechanisms for reliving memories of the death in treating PGD have not been so thoroughly articulated; however, the aim has typically been to promote the processing of death-related memories and associated affect, rather than explicitly achieving habituation or the direct reduction of distress (Shear, 2015). When reliving was initially introduced into the treatment of PGD it was loosely based on treatment of PTSD (Shear et al., 2005); however, subsequent descriptions of the reliving components have emphasized that this strategy seeks to promote connection with the deceased, reduce avoidance, rehearse coping with the emotional pain, and balance the oscillating shifts between denial of the loss and painful intrusive memories of the deceased (Shear et al., 2007, 2016). These conceptual differences are paralleled by different theoretical models of each disorder, with PTSD being characterized by fear and avoidance, and PGD being marked by longing for the deceased. There is much evidence that both PTSD (Yufik & Simms, 2010) and PGD (Eisma & Stroebe, 2021; Yu et al., 2017) can involve marked avoidance tendencies. Whereas both disorders can involve avoidance, there is some evidence that PGD can also involve approach tendencies towards reminders of the deceased (Boddez, 2018; Maccallum & Bryant, 2019; Prigerson et al., 2009). Moreover, whereas PTSD models define avoidance in terms of maintaining distance from reminders of the trauma, models of grief propose that avoidance involves minimizing awareness of the separation from the deceased rather than avoidance of memories of the death (Boelen et al., 2006).

Many studies have investigated the extent to which habituation of distress between and within prolonged exposure (PE) sessions reflects the extent to which this reduction in fear is achieved during the course of PE, and predicts remission of PTSD symptoms. There have been numerous reports of between-session habituation predicting symptom reduction (Gallagher & Resick, 2012; Rauch et al., 2004; van Minnen & Foa, 2006; van Minnen & Hagenaars, 2002), although other studies have reported that symptom reduction is not associated with remission (Bluett et al., 2014; Pitman et al., 1996). Fewer studies have noted that within-session habituation predicts treatment success (van Minnen & Hagenaars, 2002), although most studies indicate that this pattern is not associated with remission (Bluett et al., 2014; Jaycox et al., 1998; see also Craske et al., 2008).

There is currently a dearth of evidence regarding the relative roles of reliving of distressing memories in treatments of PTSD and PGD. Accordingly, the aims of this study were to compare the extent to which (1) between-session habituation occurs between treatments of PTSD and PGD, and (2) between-session habituation predicts treatment response in PTSD and PGD. To address these questions, this study compared distress ratings across PE sessions in patients who were treated for PTSD or PGD, and examined the extent to which patterns of change were associated with treatment response. On the premise that PE is predicated on the reduction of distress with repeated PE sessions, we predicted that there would be greater habituation between sessions in PTSD than in PGD, because reliving loss-related memories in treatment of PGD is not intended to achieve habituation of distress. Similarly, we predicted that habituation would be associated with symptom reduction in PTSD to a greater extent than it would be for PGD.

2. Method

2.1. Participants

Participants were 100 treatment-seeking patients who attended the UNSW Traumatic Stress Clinic for treatment for PTSD (n = 55) or PGD (n = 45). The PTSD participants participated in one of two trials that both comprised TF-CBT (Bryant et al., 2013, 2019; prospectively registered at the Australian and New Zealand Clinical Trials Registry, ACTRN12612000185864, ACTRN12609000324213). The mean ± SD age of PTSD participants (31 females, 24 males) was 41.95 ± 13.99 years; these patients were diagnosed with PTSD by master’s or doctoral level clinical psychologists using the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) version of the Clinician-Administered PTSD Scale (CAPS) (Blake et al., 1995), following assault (n = 12, 21.8%), police duties (n = 14, 25.5%), motor vehicle accidents (n = 16, 29.1%), or traumatic accident (n = 13, 23.6%), which occurred on average 49.56.0 ± 18.43 months prior to treatment. The PGD participants participated in a trial of grief-focused CBT (Bryant et al., 2014; prospectively registered at the Australian and New Zealand Clinical Trials Registry, ACTRN12609000229279). The mean age of PGD participants (33 females, 12 males) was 47.04 ± 12.21 years; these patients were diagnosed with PGD by master’s or doctoral level clinical psychologists, using a semi-structured interview based on the Complicated Grief Assessment (CGA) (Zhang et al., 2006), and had been bereaved as a result of included sudden illness (21%), chronic illness (54%), accident (14%), or suicide (11%), which occurred on average 47.42 ± 14.32 months prior to treatment. The deceased were parents (n = 16, 35.6%), partners (n = 12, 26.7%), children (n = 11, 24.4%), or others (n = 6, 13.3%). Thirty-one (56.4%) of the PTSD participants and 26 (57.8%) of the PGD participants reported major depressive disorder (MDD), as assessed by the Mini-International Neuropsychiatric Interview (MINI version 5.5) (Sheehan et al., 1998). Inclusion criteria for the PTSD trials were that participants were at least 18 years old and met DSM-IV criteria for PTSD. The inclusion criterion for the PGD trial was that participants met the diagnostic criteria given in the 11th revision of the International Classification of Diseases (ICD-11). Across both trials, exclusion criteria included a history of psychosis, current substance dependence, severe suicidal risk, inability to converse in English, and being less than 18 years of age.

2.2. Measures

2.2.1. PTSD

DSM-IV-defined PTSD symptoms were assessed using the CAPS-2 (Blake et al., 1995). The CAPS is a structured clinical interview that indexes the 17 symptoms described by the DSM-IV PTSD criteria. Each symptom is rated on a five-point scale in terms of the severity and frequency of the symptom in the past week. The CAPS possesses good sensitivity (.84) and specificity (.95) relative to the Structured Clinical Interview for DSM-IV (SCID) PTSD diagnosis, and also possesses sound test–retest reliability (.90–.98) (Blake et al., 1995).

2.2.2. PGD

PGD was assessed using the CGA (Zhang et al., 2006), which is a clinician-administered semi-structured interview based on the Inventory of Complicated Grief (Prigerson et al., 1995) and provides a diagnosis and severity index of PGD. The interview assesses for the presence of separation distress (Criterion A), difficulty accepting the death, emotional numbness, bitterness, difficulty re-engaging in life, and a sense of purposelessness and meaninglessness (Criterion B).

2.2.3. MDD

A diagnosis of depression was based on assessment with the MINI, version 5.5 (Sheehan et al., 1998).

2.3. Procedure

The projects were approved by the UNSW Human Research Ethics Committee. Following written informed consent, participants underwent treatment for PTSD or PGD. Both treatments were administered weekly on an outpatient basis by master’s or doctoral level clinical psychologists. Full details are available in the published trial manuscripts (Bryant et al., 2013, 2014, 2019). In brief, PTSD consisted of 12 individual sessions that comprised psychoeducation, six sessions of imaginal exposure, in vivo exposure, cognitive restructuring, and relapse prevention. PGD treatment followed a specific treatment manual developed for a controlled trial and has been previously reported (Bryant et al., 2014). This treatment consisted of 14 sessions that comprised 10 group sessions involving cognitive restructuring, goal setting, behavioural activation, and relapse prevention. These groups were supplemented by four individual sessions of imaginal exposure to the death or related memories. In both treatments, the reliving involved 30–40 min of reliving the experience.

In both treatment programmes, participants were asked to provide a rating of their distress on a 100-point Subjective Units of Distress Scale (SUDS) (1 = not at all distressed, 100 = extremely distressed). The treating clinician asked the participant for this rating at the start, mid-way, and at the completion of the reliving. To operationalize between-session distress, we used the mid-way distress rating because this represents the peak distress rating in each reliving session.

2.4. Data analysis

Symptom change was expressed as an arcsine-transformed proportion of baseline. SUDS scores from the midpoint of each of the four treatment sessions were modelled using a growth curve (linear trend), with slope being a random effect. Symptom change was regressed on treatment (coded as −½ for PTSD and ½ for PGD), the slope from the growth model, and the treatment × slope interaction. The model was fitted in Mplus, using the Bayesian estimator (other estimators encountered numerical problems). Results are presented as estimates and the associated 95% confidence interval (CI). The p-values are based on doubling the one-tailed values reported by Mplus. Factor scores for individuals are the mean of the plausible values drawn for each individual, from the Bayesian posterior distribution.

3. Results

3.1. Participants’ characteristics

Table 1 indicates that participants did not differ in terms of age, duration of disorder, gender distribution, rates of comorbid depression, or level of initial distress reported in the initial reliving session.

Table 1. Participants’ characteristics.

	PTSD (n = 55)	PGD (n = 45)	χ^2/t	p
Female	31 (56.4)	45 (73.3)	3.10	.08
Age (years)	41.64 ± 13.99	47.04 ± 1.82	1.92	.06
Time since trauma/death (months)	49.56 ± 18.42	47.42 ± 14.31	0.64	.52
MDD	31 (56.4)	26 (57.8)	0.02	.89
PTSD	55 (100)	25 (55.5)	30.56	.001
Anxiety disorder	26 (47.3)	17 (37.8)	0.91	.34
Substance use disorder	18 (32.7)	10 (22.2)	1.35	.24
Initial distress rating	87.51 ± 11.32	90.09 ± 10.89	1.15	.25

Note: Data are shown as n (%) or mean ± SD.

PTSD, post-traumatic stress disorder; PGD, prolonged grief disorder; MDD, major depressive disorder.

3.2. Between-session habituation

The mean of the estimated slopes (slope for SUDS) was −5.01 (−6.39, −3.63). Based on factors scores, the mean slope was greater in PTSD than in PGD [PTSD: −6.9; PGD: −2.7; Welch (unequal variance) t = 5.66, df 85.47, p < .0001]. The estimated slopes are shown by group in Figure 1. Slopes are coloured according to the quartile into which the individual change fell, and show the degree to which high change (large negative slopes) is associated with the higher amounts of change.

Figure 1. Individual slopes of change in Subjective Units of Distress Scale (SUDS) scores according to quartiles for the post-traumatic stress disorder (PTSD) and prolonged grief disorder groups.

3.3. Relationship between habituation and treatment outcome

There was no significant effect of group on symptom change (0.031, 95% CI −0.151, 0.223, p = .742), or of slope on symptom change (−0.011, 95% CI −0.028, 0.005, p = .164). There was, however, a significant effect of the group × slope interaction (0.003, 95% CI 0.001, 0.068, p = .044). Specifically, whereas between-session habituation was associated with symptom remission in PTSD patients, this association was not evident in patients with PGD. The correlation between slope and symptom change was significant in the PTSD patients (r = −.522, 95% CI −.691, −.298, p < .0001), but not in the PGD patients (r = .139, 95% CI −.161, .416, p = .139) (Figure 2).

Figure 2. Association between slopes of change in Subjective Units of Distress Scale (SUDS) scores and reduction in symptom severity for post-traumatic stress disorder (PTSD) and prolonged grief disorder groups.

4. Discussion

As predicted, PTSD participants displayed greater habituation of distress between sessions relative to PGD participants. Moreover, the decrease in distress between reliving sessions was related to reduced symptoms after treatment to a greater extent for PTSD than for PGD participants. These findings point to potential differences in the mechanisms of reliving of trauma or death-related memories in the treatment of the two conditions.

The observation that reduction in distress ratings across PE sessions was associated with greater PTSD symptom remission after treatment accords with numerous prior studies (Gallagher & Resick, 2012; Rauch et al., 2004; van Minnen & Foa, 2006; van Minnen & Hagenaars, 2002). This finding can be interpreted in terms of emotional processing theory, which holds that the integration of corrective information across PE sessions is essential for symptom remission (Foa & Kozak, 1986). The association of between-session habituation and treatment response may reflect the extent to which extinction learning occurs as the person engages in successive PE sessions, and thereby new learning is occurring that prior signals of threat are no longer threatening.

The lack of an association between habituation of distress and PGD remission accords with the theories of key different mechanisms underpinning the respective disorders. PTSD is postulated to be maintained by disruptions in fear networks that are maintained by avoidance of reminders of the traumatic event (Foa, 2006; Rauch & Drevets, 2009). Whereas models of PGD also emphasize the role of avoidance of reminders of the separation from the deceased (Boelen et al., 2006), which is supported by evidence of avoidance being a key factor in maintaining PGD (Eisma & Stroebe, 2021; Yu et al., 2017), PGD models also note the central role of separation from a key attachment figure and the disruption that this causes to one’s identity (Maccallum & Bryant, 2013). This feature of PGD is reflected by evidence that problematic grief involves neural disturbances in reward processing networks (Bryant et al., 2021; O'Connor et al., 2008), and findings that grief is associated with approach tendencies on Stroop (Maccallum & Bryant, 2010) and approach-avoidance (Maccallum & Bryant, 2019; Maccallum et al., 2015) tasks. One study of bereaved people following traumatic loss found that whereas PTSD symptoms were associated with behavioural inhibition of aversive stimuli, PGD symptoms were linked to orientation to rewarding stimuli (Williams et al., 2019). The current findings do not permit us to specify the reasons for the different patterns in PTSD and PGD treatment; however, they are consistent with proposals that PGD treatment requires processing of memories and emotions related to the death, rather than habituation. The additional processes involved in the role of reliving the loss have not been documented to date; however, future research needs to delineate how reliving memories of the death may reduce avoidance behaviours, promote integration of new appraisals about the loss, and lead to planning more adaptive future goals.

Whereas reduced distress was associated with symptom reduction in PTSD, this pattern was not observed in PGD. This observation does not undermine the utility of reliving strategies in the treatment of PGD because evidence indicates that treatment outcomes are improved when reliving is given priority (Boelen et al., 2007; Bryant et al., 2014, 2017; Eisma et al., 2015). One possible explanation for this is that reliving strategies are beneficial in PGD because they promote processing of distressing memories surrounding the loss, and this promotes adaptation (Stroebe & Schut, 1999). This interpretation is supported by evidence that reliving as a stand-alone treatment strategy is effective in reducing PGD severity (Boelen et al., 2007; Eisma et al., 2015). Another possible interpretation is that reliving memories of the death and associated issues facilitates restructuring of maladaptive beliefs about the death and provides a better opportunity for the person to engage in future planning and engagement in positive activities. This interpretation accords with evidence that providing reliving prior to cognitive restructuring leads to better outcomes than when reliving is administered following cognitive restructuring (Boelen et al., 2007).

We note some relevant limitations to our study. First, whereas the PTSD patients received between four and six sessions of PE, PGD patients only received four reliving sessions. Although we only based analyses on the initial four PE sessions, the additional PE sessions may have contributed to the different clinical outcomes between the two conditions. Secondly, the PTSD and PGD treatments both had other distinct treatment components. Specifically, PGD patients received input regarding developing positive events, social interactions, and fostering positive memories of the deceased, and these components were lacking in the PTSD treatment. Relatedly, many of the non-exposure components for PGD were delivered in a group format, whereas all PTSD therapy was conducted individually. Thirdly, we recognize that the manner in which the current treatment conducted reliving of death-related memories differs from a number of other treatment protocols that may not conduct the reliving for the duration of time or in the repeated manner that was done in the current study (Shear et al., 2005, 2016). Finally, the trials of PTSD recruited participants who met DSM-IV criteria, and the findings may not be strictly generalizable to those who meet DSM-5 criteria.

Although these findings are tentative and should be replicated in studies that address the current methodological limitations, the current observations have potential clinical implications. Clinicians traditionally apply imaginal exposure in the context of PTSD with the goal of habituation and mastery of trauma memories, which is validated by the association of diminished distress ratings during exposure and subsequent symptom reduction (Gallagher & Resick, 2012; Rauch et al., 2004). In contrast, the current findings suggest that treatment of PGD should aim for reliving of memories related to the loss without necessarily expecting reduction of the distress. Although speculative at this stage, it is possible that reliving these memories contributes to the reduction of avoidance in PGD and also promotes greater capacity to integrate cognitive restructuring and future planning. This interpretation accords with evidence that administering exposure prior to cognitive restructuring leads to better outcomes in PGD patients than when the exposure is delivered after the cognitive work (Boelen et al., 2007).

In summary, there is little doubt that the convergent evidence across trials shows that treatments comprising reliving of distressing memories is beneficial in treating both PTSD and PGD. The current findings indicate, however, that different mechanisms may be involved in how reliving benefits these two conditions. Better understanding of these distinct roles of reliving memories in PTSD and PGD would advance our knowledge on how to improve treatment of these conditions, because many patients do not respond to the treatments optimally, and augmentation of treatment may require strategies that are informed by the relevant mechanisms underpinning reliving in PGD and PTSD.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The data used in this study will be available from the corresponding author ([email protected]) after publication. Deidentified data are available at doi:10.6084/m9.figshare.21564066.

Additional information

Funding

The trials were funded by the National Health and Medical Research Council [project grant number 455341, programme grant number 568970, and number 1073041]. The funder had no role in study design, data collection or analysis, or report preparation.