Identifying latent profiles of posttraumatic stress and major depression symptoms in Canadian veterans: Exploring differences across profiles in health related functioning
Introduction
There has been a recent acknowledgment by the National Institute of Mental Health (Research Domain Criteria; RDoc) and the American Psychiatric Association (APA) that that there is an indistinct boundary between trauma or stressor-related disorders, such as Posttraumatic Stress Disorder (PTSD) and alternative disorders such as Major Depressive Disorder (MDD: APA, 2013). Indeed national epidemiological surveys estimate comorbidity rates between PTSD and MDD to range from 48% to 55% (NCS: Kessler et al., 1995; NCS-R: Kessler and Merikangas, 2004). Furthermore, both MDD and PTSD share a number of risk factors and behave similarly longitudinally (O׳Donnell et al., 2004, Norman et al., 2011). Of concern, individuals who report co-occurring PTSD and MDD are also generally those who have a more chronic profile, greater distress and impairment, and utilize mental and physical health services to a greater degree (Post et al., 2001, Ikin et al., 2010). A recent meta-analysis of 57 studies (N=6670) reported that over half of the individuals with PTSD (52%) also reported co-occurring MDD; this was more apparent in military compared to civilian samples. The current study will therefore assess the manner in which PTSD and MDD symptoms co-occur and how co-occurrence relates to health related functional impairment (HRF) in a sample of treatment seeking veterans.
A recent review of the etiology of depression comorbidity in combat-related PTSD (Stander et al., 2014) which focused on longitudinal and twin-studies, summarized three commonly proposed hypotheses which have been put forth in the extant literature. The first centers around causal hypotheses; the view that depression causes PTSD or that PTSD causes depression, the second, the common factors hypotheses; the view that both depression and PTSD result due to common risk factors, albeit the two disorders are distinct, and the third, that potential confounds may have a role in the notable comorbidity patterns; this view suggests that the two disorders are coincidentally associated. For example, the indistinct boundary between both may be attributable to poor definitions of symptomatology, thus the disorder itself (Stander et al., 2014). In conclusion, the researchers noted that more support is available for the idea that PTSD influences the development of depression compared to the reverse. In addition, it was found that common risk and vulnerabilities do indeed influence the development of PTSD and depression; yet it was acknowledged that further investigation is required. Interestingly, the authors highlighted inconsistent evidence that combat exposure may be a common risk factor for PTSD and depression. Addressing the potential confounds hypotheses it was noted that “…it is unlikely that PTSD and depression are completely indistinct diagnoses…or that they are simply sub-clusters of a larger syndrome of response to trauma…” (Stander et al., 2014; p. 94).
A number of cross-sectional studies assessing PTSD and MDD׳s comorbidity have relied on the statistical technique of Factor Analysis (Armour and Shevlin, 2010, Gros et al., 2010, Armour et al., 2011, Elhai et al., 2011a, Elhai et al., 2011b, Contractor et al., 2014). We would however argue that techniques such as Latent Class and Latent Profile Analysis (LCA and LPA, which differ in their use of categorical or continuous indictors respectively) may result in a greater degree of understanding in relation to how these two disorders co-occur. For example, LPA groups individuals into latent classes based on their similarity in responding across a number of indicators (McCutcheon, 1987). Therefore, LPA is an ideal tool to examine comorbidity given it will identify if, for example, a proportion of the sample endorses only PTSD, only MDD, or a combination of both items. Moreover, using multiple indicators allows investigators to assess how PTSD and MDD associate across all of the individual symptoms of both disorders. LPA is further advantageous in its use of continuous indicators which allow for investigations into item severity. Thus, LPA can alleviate previous methodological limitations across studies which were reliant on discrete diagnostic categories or the sole presence and absence of symptoms.
These methods have been previously utilized when examining heterogeneity in PTSD (Breslau et al., 2005, Chung and Breslau, 2008, Ayer et al., 2011, Elhai et al., 2011a, Elhai et al., 2011b) and MDD (Carragher et al., 2010; Hybels et al., 2013) symptom presentation separately. Furthermore, several studies have utilized LCA and LPA to examine how PTSD symptoms co-occur with both psychotic (Shevlin et al., 2010) and dissociative symptoms (Wolf et al., 2012a, Wolf et al., 2012b, Armour et al., 2014a, Armour et al., 2014b). To our knowledge, only a single study has conducted LPA on both PTSD and MDD symptoms concurrently (Au et al., 2013).
Au et al. (2013), in assessing PTSD and MDD data from sexual assault survivors, utilized sum scores for four well established PTSD factors (King et al., 1994 [Re-experiencing, Avoidance, Emotional Numbing, Hyperarousal]) and a measure of MDD as their LPA indicators. A 4-class model provided the best fit to the data across multiple time points. The classes highlighted that levels of PTSD and MDD mirrored each other. Most notable was that classes remained moderately stable over time and the LPA did not find a group of individuals who endorsed only PTSD or only MDD indicators. It was noted that these findings supported an earlier proposition that both disorders may represent a general distress response to traumatic experiences (O׳Donnell et al., 2004, Norman et al., 2011); with perhaps the experience of sexual assault being a common risk factor leading to the development of the two disorders (Au et al., 2013).
The current study was additionally interested in how groupings of PTSD and MDD symptoms relate to HRF. Research has consistently highlighted the relationship between trauma exposure and poor HRF (Green and Kimerling, 2003), the correspondence between PTSD symptom severity and the degree of physical health complaints (Kimerling et al., 2000), and the increased risk of morbidity in PTSD diagnosed participants, in particular veterans (Boscarino, 1997, Schnurr and Spiro, 1999, Wagner et al., 2000). Similarly, research has noted that not only do depressed patients show a greater degree of physical disability compared to non-depressed patients but that MDD has also a detrimental effect on long-term physical outcomes (Ormel et al., 1993, Beekman et al., 1995, Judd et al., 1996, Gallo et al., 1997 ). MDD may also indirectly affect HRF via an increase in health risk behaviors such as smoking, over-eating, and sedentary lifestyles (Glassman et al., 1990, Rosal et al., 2001, Goodman and Whitaker, 2002). Furthermore, comorbidity of PTSD and MDD has a greater impact on HRF (Post et al., 2001, Momartin et al., 2003) and results in long-term functional impairment (Au et al., 2013).
The first aim was to uncover underlying sub-groupings of PTSD and MDD endorsements. The second aim was to assess differential relations between groupings and reported levels of HRF. We expected to find (1) multiple PTSD and MDD groups which could be differentiated by the severity of their symptoms (Au et al., 2013) and (2) their level of HRF.
Section snippets
Participants/procedure
The current study used archival data of 424 treatment-seeking Canadian Forces (CF) members and veterans who were referred by their primary care physician (for currently serving members) or Veterans Affairs Canada case manager (for veterans) to the Parkwood Hospital Operational Stress Injury (OSI) clinic between January 2002 and May 2012.
The clinic follows a standardized intake screening protocol, which includes administering several measures including those mentioned below, to each veteran
Results
In the effective sample, the percentage of participants who met the screening criteria for probable MDD, dysthymic disorder and Depressive Disorder NOS based on PRIME MD were, 48.8 (n=138), 2.5 (n=7), and 2.5 (n=7). Further the percentage of people diagnosed with Probable PTSD based on the PTSD Checklist-Military Version (PCL-M) was 56.9 (n=161). The mean scores for the SF-36 subscales were as follows: physical functioning (M=42.17, S.D.=26.1), role limitations due to physical health (M=31.88,
Discussion
Using LPA we were able to identify three distinct classes based on how participants responded across 17 PTSD and nine MDD items in our sample of Canadian military veterans. This differs to a previous study assessing PTSD and MDD co-occurrence (Au et al., 2013) in which four latent classes were deemed optimal. Notably, both the current study and Au et al.׳s study reported classes with increasing symptom severity in the absence of qualitative differences in item endorsement. There were however
Author disclosures
This manuscript received no funding. We have no acknowledgement to makes. Nor do we have any conflicts of interest to report.
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