Interpersonal psychotherapy for bereavement-related major depressive disorder in Japan: a pilot study

Abstract

Bereavement-related major depressive disorder (MDD) is common in Japan; however, no established therapies have been adapted to the unique Japanese cultural norms and practices. Interpersonal psychotherapy (IPT) has established efficacy for MDD; hence, we developed an adapted IPT program and conducted a pilot study, including six patients with bereavement-related MDD confirmed using the Mini International Neuropsychiatric Interview. Depressive symptoms, comorbid psychiatric disorders and grief-related avoidance behaviors were measured at baseline and immediately, three months and six months after treatment. All participants completed treatment without any severe adverse events. Exploratory analyses using the linear mixed-effects model revealed significantly improved depressive symptoms assessed by the Patient Health Questionnaire 9 at three months and trends for improvement immediately and six months posttreatment. Our results suggest preliminary evidence of the feasibility and safety of IPT for Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition MDD without or with mild features of comorbid anxiety, depression, or trauma-related disorders.

Impact Statement

Bereavement-related major depressive disorder (MDD) is common in Japan; however, no established therapies have been adapted to the unique Japanese cultural norms and practices. This is the first report examining the feasibility, safety, and preliminary effectiveness of a culturally adapted Interpersonal psychotherapy program for Japanese patients with bereavement-related MDD.

Keywords:

• Interpersonal psychotherapy
• bereavement
• depression
• grief
• Japan

Reviewing Editor:

• Daryl O’Connor, United Kingdom

Subjects:

• Social Sciences; Area Studies; Asian Studies; Behavioral Sciences; Psychological Science; Mental Health

Introduction

Bereavement is one of life’s most serious stressors (Holmes & Rahe, 1967; Keyes et al., 2014). Grief, the painful emotional response to the death of a loved one, is considered normal and even helpful for coping. Grief varies in frequency and intensity and usually peaks approximately six months after the death of a loved one (Maciejewski et al., 2007). In some cases; however, bereavement-related grief progresses to clinical depression. An important change to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) was removal of the bereavement exclusion criterion from the diagnostic criteria for major depressive disorder (MDD). In the precursor DSM, Fourth Edition, Text Revision (DSM-IV-TR), a bereavement-related depressive episode was considered clinical depression only if typical symptoms (eg depressed mood, loss of interest or pleasure, loss of energy or fatigue and worthlessness or guilt.) lasted for at least two months after passing of the loved one. Alternatively, the diagnosis of MDD is permitted during bereavement according to DSM-5, with a footnote provided for guidance.

Due to the lack of explicit exclusion criteria in the footnote, however, there is a heavy onus on clinical judgment in the diagnostic process (Wakefield, 2016). In the footnote, it is specified that ruminations be self-critical rather than preoccupied with the deceased as observed in normal grief. In addition, if the bereaved thinks about dying, the thought is typically centered on joining the deceased in normal grief, whereas in bereavement-related MDD, this thought is centered on terminating one’s own life due to feelings of worthlessness and being undeserving of life. These changes in diagnostic criteria, which are retained in the new DSM‐5 Text Revision (DSM-5-TR), are still widely debated due to concerns about overdiagnosis or ‘medicalizing’ grief. Therefore, a clinician evaluating the bereaved must be careful not to pathologize normal grief but also not to discount possible MDD and the need for treatment (Pies, 2014; Shear et al., 2011).

Barry et al. (2002) reported that 9% of bereaved family members in the United States met the full diagnostic criteria for MDD at four months after passing of the loved one and that 5.7% still met these criteria at nine months. Furthermore, Ling and coworkers reported depressive symptoms in 59% of bereaved family members at 1 month, in 47% at 3 months, 42% at 6 months and in 39% at 12 months after death in China (Ling et al., 2013). In Japan, the leading cause of death is cancer, and depressive symptoms were reported in 22% of the family members after cancer death, whereas 9% of the family members reported complicated grief, previously termed as pathological or traumatic grief and now referred to as prolonged grief disorder (PGD) in DSM-5-TR (Aoyama et al., 2021). Study performed by Aoyama et al. included 21%, 60%, 14%, 4% and 1% of family members who bereaved for <6 months, 6–12 months, 1–1.5 years, 1.5–2 years and 2–2.5 years after having lost a loved one, respectively. Bereavement-related MDD may also be complicated by symptoms of other psychiatric disorders. Komischke-Konnerup et al. (2021) reported symptoms of complicated grief with clinically relevant depressive symptoms in 63% participants (bereaved adults ≥18 years) and symptoms of complicated grief with PTSD symptoms in 49% participants. Furthermore, great psychological distress associated with bereavement, such as bereavement-related depression or other psychiatric disorders, increases the risk of serious physical disorders, such as cardiovascular and cerebrovascular events (Stroebe et al., 2007; Zisook et al., 2014), and mortality due to many causes, including suicide (Stroebe et al., 2007). Thus, more effective treatments targeting bereavement-related depression and comorbid symptoms are urgently required.

Psychotherapies such as cognitive behavioral therapy and interpersonal psychotherapy (IPT) are considered equally effective for MDD in multiple contexts, including bereavement (Zisook et al., 2014), but relative few studies have actually evaluated the efficacies of these treatments specifically for bereavement-related depression (Johnson et al., 2016; Reynolds et al., 2004). Nonetheless, many therapists around the world use IPT for bereavement-related MDD based on established efficacy for MDD of other etiologies (Cuijpers et al., 2011). In addition, a recent systematic review and meta-analysis suggested that IPT may be an effective intervention for reducing the symptoms of PTSD (Althobaiti et al., 2020). Interpersonal therapy has also been shown to be effective for complicated grief, although it is inferior to specialized complicated grief therapy (K. Shear et al., 2005; M. K. Shear et al., 2014).

Unfortunately, IPT is rarely offered for bereavement-related MDD in Japan because there are relatively few IPT practitioners and the National Health Insurance Plan does not cover IPT, in part due to the lack of demonstrated efficacy in controlled clinical trials (Akechi et al., 2022). Thus, pharmacotherapy and supportive psychotherapy, which are covered by the National Health Insurance Plan, are the mainstays of treatment for bereavement-related MDD. The content of IPT for bereavement-related MDD requires adaptation to specific contexts because of the unique views of life and death, the norms of emotional expression during grieving and mourning and the relationship with the deceased across cultures (Hsu et al., 2002; Moayedoddin & Markowitz, 2015; Wikan, 1990; Yamamoto et al., 1969). Wikan (1990) reported that the laughter and jovial atmosphere during Balinese (Indonesian) bereavement ceremonies were not because of the bereaved family members’ lack of grief, but because public expression of grief was culturally inappropriate. Therefore, the laughter of the bereaved could be considered a forced attempt to suppress feelings of grief. Additionally, Balinese bereavement rituals are conducted based on the Hindu religion, which strongly affirms the afterlife, including reincarnation. In Japan, Shintoism and Buddhism have been integrated and harmonized, with many Japanese individuals adopting Buddhist methods for bereavement rituals. During postmortem rituals, such as the first 49 days after death and the first death anniversary, the Japanese bereaved family members feel freer to express their grief, share their sorrow with relatives and gradually accept the deceased’s death. Other cultures have formal mourning rituals as well. In fact, traditional Jewish bereaved family members mourn at shiva after the funeral and share stories about the deceased with those connected to them, whereas Catholic bereaved family members offer special masses for the deceased. Notably, Japanese death culture believes that the deceased has not returned to nothingness but exists as a soul in the afterlife and that the bereaved can have a relationship with the deceased through tablets, Buddhist altars and graves (Sakaguchi, 2022). The current study examined the feasibility and safety of a culturally adapted IPT program for bereavement-related MDD in a Japanese clinical setting. Moreover, we examined the preliminary effectiveness of IPT for decreasing symptoms of depression, posttraumatic stress, panic disorder and clinically impairing grief.

Materials and methods

Patient selection

We conducted a single-arm study on the feasibility, safety and preliminary effectiveness of a culturally adapted IPT program for bereavement-related MDD. The study was performed in accordance with the Declaration of Helsinki, and the study protocol was approved by the ethics committee of Nagoya City University Graduate School of Medicine (60-20-0088). Written consent was obtained from all participants.

Eight individuals who had lost a significant other were recruited from a general hospital Department of Psychiatry, two mental health clinics, the Department of Psychiatry and the Outpatient Grief Care center at a university hospital and a psychiatry-specialized hospital between July 2021 and July 2022. All candidates visited the Department of Psychiatry at Nagoya City University Hospital or Minami-chita Hospital and were assessed by an experienced psychiatrist (YT or MK) according to the following inclusion and exclusion criteria. The inclusion criteria were (i) age of 20–75 years, (ii) a principal diagnosis of MDD (first episode or recurrent) according to DSM-5 criteria using the Mini International Neuropsychiatric Interview 7.0.2 (MINI-7) and (iii) onset of bereavement-related MDD between 6 months before the death of a significant other and 12 months after the death. Onset time was defined according to a previous randomized clinical trial (RCT) on IPT for bereavement-related major depressive episodes (Reynolds et al., 2004). The exclusion criteria were (i) neurodevelopmental disorders, schizophrenia and related disorders, bipolar and related disorders, obsessive–compulsive and related disorders, neurocognitive disorders and personality disorders according to DSM-5 criteria, (ii) active suicidality, (iii) previous IPT treatment or planning to receive other structured psychotherapies other than supportive counseling and (iv) difficulty communicating with clinicians in Japanese due to lack of proficiency in the Japanese language or intellectual deficiencies. Regarding exclusion criterion (i), individuals with certain psychiatric disorders for which IPT was not at all or only marginally effective were excluded considering that such psychiatric disorders required alternative approaches. No inclusion/exclusion criteria for psychopharmacological prescriptions were available. Of the eight candidates, one did not meet the principal diagnosis of DSM-5 MDD as assessed by the MINI-7 (depressive symptoms were in remission) and one experienced onset outside the set period (MDD onset was triggered by interpersonal relationships at work three years after bereavement). Ultimately, we enrolled six patients with confirmed bereavement-related MDD.

Clinical measures

Comorbid PTSD, panic disorder (PD), social anxiety disorder, generalized anxiety disorder and eating disorders were assessed according to DSM-5 criteria using MINI-7. Comorbid DSM-5 persistent complex bereavement disorder (PCBD), which was recently superseded by PGD in the DSM-5-TR (Section 2, trauma- and stressor-related disorders chapter) was assessed according to the DSM-5 Section III (ie among ‘conditions for further study’) by an experienced psychiatrist (YT or MK).

To evaluate the feasibility of the adapted IPT program, we carefully assessed reasons for dropout, while safety was assessed by monitoring the occurrence and course of adverse events such as acute suicidality, suicide attempt, life-threatening medical conditions requiring inpatient hospitalization or potentially resulting in permanent impairment and suicidal ideation according to the Patient Health Questionnaire 9 (PHQ-9). These evaluations were conducted once every four sessions. In addition, we carefully monitored therapists’ adherence to both manualized treatment (Weissman et al., 2000) and treatment strategies (Toshishige et al., 2022) that considered Japanese culture. Psychological and clinical scales were assessed at baseline (pretreatment), immediately posttreatment, three months posttreatment and six months posttreatment.

Patient Health Questionnaire-9

The PHQ-9 is a widely applied nine-item self-report scale for assessing depression severity in both clinical practice and scientific research (Kroenke et al., 2001), and the Japanese version used here has demonstrated good reliability and validity (Muramatsu et al., 2018). Responses were scored from 0 to 3, yielding a total score between 0 and 27. A score of 10 or higher is considered a valid cutoff for moderate-to-severe depression (Kroenke et al., 2001).

Posttraumatic Diagnostic Scale (PDS)

The PDS is a widely accepted four-part self-report measure based on the DSM-IV diagnostic criteria for PTSD (Foa, 1995; Foa et al., 1997) that provides an estimate of PTSD severity. Parts 1 and 2 evaluate traumatic experiences, reflecting Criterion A of the DSM-IV, while Part 3 evaluates PTSD severity during the past month, reflecting Criteria B, C and D of the DSM-IV, and Part 4 evaluates functional impairments associated with PTSD symptoms. Responses in Part 3 were scored between 0 and 3, yielding a total score between 0 and 51. A higher score is considered indicative of greater PTSD symptom severity. The Japanese version used in the current study has confirmed validity and good reliability (Itoh et al., 2017; Nagae et al., 2007). The PDS was administered only to patients with a diagnosis of comorbid PTSD as assessed by MINI-7.

Panic Disorder Severity Scale-Self-report version (PDSS-SR)

The PDSS-SR is a seven-item self-report measure designed for assessing PD symptom severity (Houck et al., 2002). Responses were scored from 0 to 4, yielding a total score between 0 and 28. A total score of 4 or less indicates remission. The Japanese version used in this study has good reliability and validity (Katagami, 2007). The PDSS-SR was administered only to patients with a diagnosis of comorbid PD as assessed by MINI-7.

Inventory of Complicated Grief (ICG)

The ICG is a 19-item self-report measure of clinically impairing grief symptom severity (Prigerson et al., 1995). Responses were scored from 0 to 4, yielding a total score between 0 and 76. A score ≥26 (Prigerson et al., 1995) or ≥30 (K. Shear et al., 2005; M. K. Shear et al., 2014) has been used as a conservative threshold to identify clinically significant cases (Cozza et al., 2016). In this study, we used the cutoff indicated in the study by Prigerson et al. The Japanese version used in this study has good reliability and validity (Nakajima et al., 2010). The ICG was administered only to patients with a diagnosis of comorbid PCBD.

Grief-Related Avoidance Questionnaire (GRAQ)

The GRAQ is a 15-item self-report measure of grief-related avoidance behaviors (K. Shear et al., 2007) such as avoiding people, places, or topics that bring back memories of the deceased. Responses were scored from 0 to 4, yielding a total score between 0 and 60, with higher scores indicating greater grief-related avoidance behaviors.

Treatment

Each patient attended 16, 60-min individualized treatment sessions with two experienced therapists (YT and MK) (Weissman et al., 2000). Sessions were scheduled weekly, but on rare occasions were delayed by one week due to unavoidable circumstances. Both therapists were trained and supervised by HM, an International Society of Interpersonal Psychotherapy (ISIPT) certified trainer/supervisor. Subsequently, YT was certified as a trainer/supervisor and MK as a supervisor by ISIPT in July 2022.

Interpersonal relationships can influence depressive symptoms, while depressive symptoms can distort interpersonal relationships. The goal of IPT is to help the patient address difficult life events or interpersonal problems by bridging the gaps in expectations between patients and those around them, by improving communication and by building social support. For these purposes, IPT therapists use techniques such as therapeutic emotional exploration of current distress, validation of relevant feelings, brief psychoeducation and communication analysis. In this study, we built on the foundation of trust established with our patients and conducted a detailed interpersonal inventory. In general, after that, a therapist identifies one or two out of four interpersonal problem areas (grief, interpersonal role disputes, role transitions and interpersonal deficits/sensitivity) that contribute to the onset and persistence of symptoms. Grief is identified as the interpersonal problem area when the occurrence of depression is associated with the death of an important attachment and the patient finds it difficult to accept the loss. Moreover, grief along with another interpersonal problem may be identified when bereavement-related MDD seems to be sustained not only by death, but also by another interpersonal problem. In this study, ultimately, the interpersonal problem area for all six participants who had bereavement-related MDD and received IPT was identified as grief alone. Therefore, interventions were implemented according to the strategies recommended for grief as one of the problem areas (Weissman et al., 2000). As the first strategy, in order to facilitate the grieving process, we encouraged the patient to express how they felt before and after their significant other’s death. As another strategy, in order to enhance social support and counter the patient’s depressed social withdrawal, we explored the possibility of reestablishing interests and relationships.

Perspectives on life and death and the expression of emotions during the grieving and mourning process vary across cultures (Hsu et al., 2002; Moayedoddin & Markowitz, 2015; Wikan, 1990; Yamamoto et al., 1969) and cultural differences influence the IPT strategies. Therefore, we conducted culturally adapted IPT (Toshishige et al., 2022). First, we devised a cultural adaptation of the first strategy. The therapist encouraged the expression of grief and sharing of feelings with relatives at Buddhist memorial services as the patient is more likely to express grief at this time. This step is critical because Japanese culture emphasizes harmony as well as individual happiness and many avoid expressing grief even after bereavement, especially in public, to maintain harmony, but feel freer to express grief and share sorrow with relatives during cultural after-death rituals. Second, we devised a cultural adaptation that spans both the first and second strategies. In the Japanese Buddhist tradition, it is believed that the deceased exists as a soul in the afterlife and that one can maintain a relationship with the deceased through the Buddhist memorial tablet, altar and grave. Therefore, we explored this relationship, including unresolved conflicts and expectations of the relationship and discussed ways of coping with the patient. This aim was to reestablish the relationship with the deceased differently than before death and to facilitate the grieving process.

Follow-up sessions of approximately 10–30 min were held every two to five weeks at the patient’s convenience (according to work or family circumstances) for six months after completion of IPT treatment. All patients had no restrictions regarding the changes in their psychopharmacological prescriptions as required during this study.

Statistical analysis

Linear mixed-effects models (LMMs) with repeated measures were constructed to examine changes in psychometric scale scores (indicating DSM-5 MDD severity, clinically impairing grief symptom severity, grief-related avoidance behaviors and PTSD symptom severity) immediately posttreatment, at three months posttreatment and at six months posttreatment relative to baseline. We then included participants as a random effect. Effect sizes for changes in clinical scores between baseline (pretreatment) and the three posttreatment time points were calculated using Cohen’s d for paired samples (Lakens, 2013). We calculated the effect size for completers using the formula d = (Mpre – Mpost)/sDdiff, where sDdiffs is the standard deviation of difference scores. All statistical tests were two-tailed, and a p < .05 was considered statistically significant. The multiplicity of tests was not adjusted because this was a pilot study. All statistical analyses were conducted using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA).

Results

Patient characteristics

Baseline demographic and clinical characteristics of the six patients (three males and three females) are summarized in Table 1. All patients presented with moderate or severe depressive symptoms as indicated by a PHQ-9 score ≥10 (Kroenke et al., 2001). Five patients also presented with moderate-to-severe comorbid PTSD, as indicated by a PDS score of ≥21 (McCarthy, 2008) related to a violent death (accident or suicide) and intrauterine fetal death (miscarriage or stillbirth) of significant others. Of these five patients, two also met the cutoff score of ≥5 for PD (Houck et al., 2002) and the cutoff score of ≥26 for PCBD (Prigerson et al., 1995), and one met the score criterion for PCBD (Prigerson et al., 1995). A total of five patients used antidepressants, four of them received single antidepressant and one patient received two different types of antidepressants, without dose change from six weeks before therapy to six-months posttreatment. Medications included drugs for insomnia and anxiolytics, as needed according to the patient’s symptoms, such as insomnia and anxiety, during this study. None of the patient received psychopharmacological prescriptions, except antidepressants, medications for insomnia and anxiolytics.

Table 1. Baseline characteristics of the participants (n = 6).

Characteristic	Number, mean, or median
Age, years: mean (SD), median (range)	45.00 (11.66), 44 (32–61)
Male gender: n	3
Marital status: n
Never married	2
Married	2
Widowed	2
Education: n
High school graduate	3
Junior college/university graduate	3
Current employment: n
Full-time	1
Self-employed	1
Housewife	1
Leave of absence	2
Unemployed (including students)	1
Family form: n
Living alone	1
With family	5
Time since the death: n
<6 months	3
6–12 months	0
1–5 years	1
5–10 years	2
Bereavement-related MDD duration, months: median (range)	6.50 (2–110)
Relationship of deceased: n
Spouse	2
Parent	2
Fetus	2
Cause of death: n
Accident	1
Suicide	2
Intrauterine fetal death	2
Sickness	1
Co-occurring current psychiatric disorder: n
Yes	5
PTSD	5
PD	2
PCBD	3
Medication
Yes	5
Antidepressants	5
Anxiolytics	1
Medications for insomnia	3

Abbreviations: SD: standard deviation; PTSD: posttraumatic stress disorder; PD: panic disorder.

Outcome

All six patients completed the treatment. Although five of the six patients had suicidal ideation (a score of 1 or higher on the PHQ-9 suicidal ideation item) at least once during treatment, there were no adverse events or severe adverse events such as acute suicidality or suicide attempt from pretreatment to six-month posttreatment.

Mean psychometric test scores at all four measurement times are presented in Table 2 and Figures 1, 2 and 3. Linear mixed models revealed significantly reduced PHQ-9 depression severity at three months posttreatment (p < .05) and a trend for lower PHQ-9 depression severity both immediately posttreatment (p = .077) and six months posttreatment (p = .070). In addition, LMMs revealed trend for lower PDS posttraumatic stress severity from immediately posttreatment (p = .146) to six months posttreatment (p = .215). Of the two participants with comorbid PD, the PDSS-SR severity score of one decreased from 14 at baseline to 0 starting immediately posttreatment and persisting until six months posttreatment, while the PDSS-SR severity score of the other patient remained unchanged at 17 up to six months posttreatment. Of the three participants with comorbid PCBD, one demonstrated a substantial drop in ICG score from 43 before treatment to 21 immediately posttreatment and 20 at six months posttreatment, one a drop from 55 before treatment to 40 immediately posttreatment and 42 at six months posttreatment and the third a modest drop from 28 before treatment to 22 immediately posttreatment and 24 at six months posttreatment. Thus, two of the three participants demonstrated a drop in ICG score under the conservative threshold for identifying clinically significant cases (≥26) (Prigerson et al., 1995) at six months posttreatment. Furthermore, LMMs showed a trend for reduced GRAQ-measured grief-related avoidance behaviors immediately posttreatment (p = .733), three months posttreatment (p = .398) and six months posttreatment (p = .185).

Figure 1. Mean scores (SD) for the Patient Health Questionnaire-9 (PHQ-9) at all four time points.

Figure 2. Mean scores (SD) for the Posttraumatic Diagnostic Scale (PDS) at all four time points.

Figure 3. Mean scores (SD) for the Avoidance of Grief-related Avoidance Questionnaire (GRAQ) at all four time points.

Table 2. Mean scores (SD) for the four time points and within-group effect sizes.

		Time point
Measure	Statistics	Pretreatment (n = 6)	Immediately posttreatment (n = 6)	3 Months posttreatment (n = 6)	6 Months posttreatment (n = 6)
PHQ-9	Mean (SD)	16.8 (2.5)	10.5 (6.3)	10.0 (6.0)	10.8 (6.5)
	Mean change from pre (95% CI)	−	−6.3 (−13.7, 1.0)	−6.8 (−12.7, −0.9)	−6.0 (−12.7, 0.7)
	p Value vs. pre	−	.077	.031*	.070
	Effect size, d	−	−0.91	−1.21	−0.94
PDS	Mean (SD)	20.3 (10.2)	14.0 (9.8)	16.2 (11.0)	13.3 (12.5)
	Mean change from pre (95% CI)	−	−6.3 (−15.8, 3.2)	−4.2 (−13.9, 5.6)	−7.0 (−19.7, 5.7)
	p Value vs. pre	−	.146	.323	.215
	Effect size, d	−	−0.70	−0.45	−0.58
GRAQ	Mean (SD)	26.7 (9.0)	25.2 (6.7)	22.0 (7.3)	19.2 (8.0)
	Mean change from pre (95%CI)	−	−1.5 (−12.2, 9.2)	−4.7 (−17.7, 8.3)	−7.5 (−20.0, 5.0)
	p Value vs. pre	−	.733	.398	.185
	Effect size, d	−	−0.15	−0.38	−0.63

Abbreviations: SD: standard deviation; CI: confidence interval; PHQ-9: Patient Health Questionnaire-9; ICG: Inventory of Complicated Grief; PDS: Posttraumatic Diagnostic Scale; GRAQ: Avoidance of Grief-related Avoidance Questionnaire.

p Values were derived from liner mixed-effects models. *p < .05.

Discussion

In this pilot study, we examined the feasibility, safety and preliminary effectiveness of an IPT program for bereavement-related MDD adapted for the Japanese clinical setting. All six patients completed the treatment, consistent with high feasibility. Although we included patients with moderate-to-severe symptoms of depression with comorbidities such as PTSD, PD and PCBD, no serious adverse events occurred, suggesting safety sufficient for outpatient settings. Exploratory analyses revealed trends for depressive and comorbid symptom improvements up to six months after the end of treatment. In contrast, no patient exhibited deterioration of symptoms, underscoring the potential effectiveness of this program.

The high feasibility and safety of this culturally adapted IPT program, as indicated by the 0% dropout rate and absence of adverse events, is consistent with previous studies on IPT for MDD of other etiologies. Markowitz et al. (2015) reported a lower dropout rate during IPT (20%) than during prolonged exposure (50%), a validated type of cognitive behavioral therapy, in PTSD patients with comorbid MDD. Similar to the cohort studied by Markowitz et al., most of the patients in the current study (5 of 6) were diagnosed with comorbid PTSD. In addition, Markowitz et al. found that IPT was noninferior to Prolonged Exposure for PTSD. K. Shear et al. (2005) also reported a relatively low dropout rate during IPT for patients with complicated grief, including patients with comorbid MDD or PTSD (26%) and found that IPT dropout rate did not differ from that of targeted CGT (27%), which includes techniques for retelling the story of the death (termed ‘revisiting’) and exercises entailing confrontation with avoided situations, analogous to techniques used for PTSD treatment but not used in IPT. Furthermore, only 1 of 46 participants who started undergoing IPT in the study by Shear et al. dropped out of IPT owing to hospitalization for active suicidal ideation. Similarly, of the three DSM-5 MDD patients with both PCBD and PTSD in our study group, none dropped out due to adverse events. However, K. Shear et al. (2005) and M. K. Shear et al. (2014) also reported a higher response rate and faster effects using CGT compared to IPT, suggesting that our program requires further refinement.

Explorative analyses revealed an overall trend for depressive and comorbid PTSD symptom improvement lasting at least six months, and these improvements were observed in more than half of the patients with comorbid PD or PCBD. Therefore, as in previous studies (Johnson et al., 2016; Markowitz et al., 2015; K. Shear et al., 2005; M. K. Shear et al., 2014), multiple psychiatric disorders may have been addressed directly or indirectly by IPT. Although the mechanisms underlying the preliminary effectiveness of IPT are unclear, we speculate that reduced avoidance behaviors may have contributed to the alleviation of MDD and comorbid symptoms by allowing participants to confront their grief and other issues related to the loss of a loved one.

In Japan, when a baby less than 12 weeks of gestation is lost, the mother and father are simply not acknowledged as ‘parents’ but rather as ‘individuals’ who had a miscarriage. In contrast, delivery of a stillborn baby after 12 weeks of gestation or over is called ‘stillbirth’ and necessitates the submission of a stillbirth report. In the case of a stillbirth, the mother and father are acknowledged as ‘parents’ and make offerings by placing the remains in their homes or in graves. Despite the recent recognition of the importance of psychological support for women who have experienced miscarriages or stillbirths, both miscarriages and stillbirths are still often regarded as taboo. Whether or not individuals are recognized as ‘parents’ and miscarriages and stillbirths are considered taboo in society may affect the grieving process. Two participants who experienced intrauterine fetal deaths in the current study were categorized as stillbirths. Therefore, they were recognized and identified themselves, as ‘parents’, which may have had some positive effect on facilitating their grieving process.

This study had several limitations. First, the small sample size limits the generalizability of the current findings. Second, the time since the loss of a loved one was rather heterogenous and ranged from <6 months to 10 years. When the time since the loss of a loved one was long, other potential factors (eg discord with family members) aside from the loss could have influenced the depressive symptoms. Unfortunately, the treatment provided in this study could not account for other potential factors, indicating that focusing our treatment on grief alone could have been inadequate. Third, as with many pilot studies, we did not include a comparison group receiving another treatment modality (or no specific clinical treatment). Thus, we cannot distinguish improvements related to IPT from placebo effects or natural healing. Moreover, it was difficult to differentiate the improvements related to IPT from concomitant pharmacotherapy, although there was no change in antidepressant medications from six weeks before therapy to six-months posttreatment. Fourth, the frequency and duration of maintenance treatment after the completion of all 16 IPT sessions varied from two to five per week for 10 to 30 min depending on the patient’s situation. Therefore, some patients may have derived additional clinical benefits during the six-month follow-up. Although no difference in recurrence rate or time to recurrence was observed among patients with different session frequencies, maintenance IPT is believed to have a measurable therapeutic effect (Frank et al., 2007). A randomized controlled study holding the frequency and duration of maintenance treatment constant is required to examine the effectiveness of IPT compared to other psychotherapies. Fifth, when the DSM-5-TR was published in March 2022 and PCBD was replaced by PGD, which is an official diagnosis, this study was already underway, therefore, PCBD, which had not been an official diagnosis, was evaluated as comorbidity with bereavement-related MDD in this study. The diagnostic criteria for PCBD and DSM-5-TR PGD differ slightly; for example, fewer symptom combinations meet the criteria for DSM-5-TR PGD diagnosis than PCBD diagnosis. Sixth, the ICG used as the self-report instrument for clinically impairing grief symptom severity is not validated for PCBD and does not reflect the newest DSM-5-TR criteria for PGD, and this should be addressed in further studies. However, neither the Prolonged Grief Disorder-13-Revised (PG-13-R) (Prigerson et al., 2021) nor the Traumatic Grief Inventory-Clinician Administered (TGI-CA) (Lenferink et al., 2023) that allows evaluation of the newest DSM-5-TR criteria for PGD has a Japanese version. Nonetheless, further studies are required to diagnose PGD according to the DSM-5-TR diagnostic criteria using PG-13-R or TGI-CA once such a translation becomes available.

Conclusions

This is the first report examining the feasibility, safety and preliminary effectiveness of a culturally adapted IPT program for Japanese patients with bereavement-related MDD using reliable clinician and self-report measures. Our results suggest preliminary evidence of the feasibility and safety of IPT for DSM-5 MDD without or with mild features of comorbid anxiety, depression, or trauma-related disorders. Psychometric testing at multiple times posttreatment revealed trends for long-term improvements in depressive and comorbid psychiatric symptoms as well as a reduction in grief-related avoidance behaviors. However, larger-scale RCTs are required to confirm the actual effectiveness of this program and identify areas of improvement.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The participants of this study did not give written consent for their data to be shared publicly. Therefore, due to the sensitive nature of the research, supporting data is not available.

Additional information

Funding

This study was supported by the Japan Society for the Promotion of Science [KAKENHI Grant Number 19K14452].

Notes on contributors

Yuko Toshishige

Yuko Toshishige is a psychiatrist, trainer and supervisor of IPT.

Masaki Kondo

Masaki Kondo is a psychiatrist and IPT supervisor.

Yoshinori Ito

Yoshinori Ito is a psychologist with expertise in bereavement care.

Hiroya Hashimoto

Hiroya Hashimoto is an expert in statistical analysis.

Junya Okazaki

Junya Okazaki is a psychiatrist with expertise in IPT and cognitive behavioral therapy.

Takuya Okami

Takuya Okami is a psychiatrist specializing in IPT.

Hiroko Mizushima

Hiroko Mizushima is a psychiatrist, trainer and supervisor of IPT.

Tatsuo Akechi

Tatsuo Akechi is a professor in the Department of Psychiatry and Cognitive-Behavioral Medicine, Nagoya City University Graduate School of Medical Sciences.