Post‐traumatic stress disorder as moderator of other mental health conditions
Authors: Richard A. Bryant
Journal: World Psychiatry (2022)

The comorbidity of post-traumatic stress disorder (PTSD) with a range of other mental disorders is common. This comorbidity is often attributed to either overlapping symptoms between PTSD and other disorders or to the variety of psychiatric conditions that can arise in the wake of exposure to a traumatic experience. However, this comorbidity may also be due to the fact that PTSD can moderate the onset or severity of other psychiatric symptoms or disorders. This is an important issue, because it has implications for how patients affected by the array of symptoms that can emerge after trauma may be most efficiently managed. Our knowledge of how PTSD can impact other disorders rests on longitudinal studies that have assessed PTSD and other conditions, and have typically conducted cross-lagged or time-series analyses. This approach allows us to determine the extent to which each condition impacts other disorders at later assessments. Convergent evidence indicates that PTSD can precede or exacerbate depression, anxiety disorders, suicidality, substance abuse, eating disorders, and psychosis1. Furthermore, PTSD can precede a range of physical and behavioral indicators, including chronic pain and tobacco use. There is also evidence from network analysis indicating how symptoms of PTSD may impact other psychiatric symptoms. Network analysis conceptualizes psychopathological states as resulting from causal paths between different symptoms – rather than emerging from an underlying disease state2, 3. For example, the PTSD symptom of nightmares may play a causal role in contributing to sleep disturbance, which in turn leads to concentration deficits and irritability. Numerous studies using network analysis have shown that specific PTSD symptoms can influence problems across other conditions, including depression and anx­iety disorders4. In explaining the role of PTSD as a mediator of the relationship between trauma exposure and onset of other psychiatric disorders, there are several mechanisms that can be considered, and these arguably function in an interactive manner. One key potential mechanism is the impact of PTSD on the capacity to down-regulate emotional distress. It is well documented that PTSD involves impaired emotion regulation, and it is possible that this impairment predisposes people to develop new psychiatric disorders or worsens others5. The capacity to regulate emotions in PTSD can be related to the well-documented deficits in executive functioning6. Deficient working memory and attentional capacity can limit the extent to which one can regulate emotions, which can result in greater risk for mental health problems. Moreover, avoidance is a key symptom of PTSD, and this can trigger a cascade of strategies that can be maladaptive. Avoidance can involve situations or thoughts and memories related to the traumatic experience. This tendency can generalize to more pervasive avoidance of social networks, emotional states, and activities that promote good mental health. This can lead to a worsening of depression, anxiety and other psychiatric conditions. Another common form of avoidance for people with PTSD is self-medicating with prescription or non-prescription substances to numb the distress that is experienced along with traumatic memories. This behaviour can not only lead to substance abuse, which has been documented in longitudinal studies of PTSD, but also facilitate other psychiatric problems, because issues may not be addressed in a constructive manner. Avoidance tendencies can also result in not seeking help from mental health services, which can impede early intervention or adequate treatment for other psychiatric disorders. The DSM-5 explicitly recognizes the presence of harmful behaviors in PTSD, including such risk-taking behaviors as dangerous driving, severe alcohol use, and self-harm. These reactions are conceptualized as a result of the extreme arousal and the difficulties in impulse control that can be experienced by people with PTSD7. These behaviors can lead to a range of events and habits triggering repetitive cycles of exposure to trauma. This can compound the sensitization that has been reported in PTSD, in which the condition results in neural sensitivity to threats and stressors in one's environment, such that the person is more reactive to these events. One of the strongest transdiagnostic predictors of risk for mental health problems is represented by maladaptive or catastrophic appraisals about oneself or the environment8. A key feature of PTSD is the tendency to engage in catastrophic appraisals after the traumatic experience, and these appraisals can generalize to many aspects of a person's life, such as one's self-esteem, trust in others, fears of negative evaluations, germs, or self-blame. These cognitive tendencies are major risk factors for an array of psychiatric conditions, including anxiety, depression, eating disorders, and obsessive-compulsive disorder. Relatedly, the tendency to ruminate is well documented after trauma, and this habit of repeatedly thinking about negative events is a major risk factor for many psychiatric conditions. In considering these various mechanisms for how PTSD can moderate other psychiatric problems, it is worth noting that many of the risk factors reviewed here may be present prior to trauma exposure, and in fact predispose the person to developing PTSD. These elements can be intensified as PTSD develops, and then contribute to other psychiatric conditions which have a shared vulnerability. In this context, it is especially worth recognizing the emerging evidence on shared genetic vulnerabilities to a range of psychiatric disorders9. In the wake of trauma exposure and PTSD development, gene expression can predispose an individual to develop other psychiatric disorders by means of the shared genetic vulnerability. Overall, this evidence reflects the interactive multifactorial nature of the processes explaining how PTSD can lead to the onset or worsening of other psychiatric conditions. Understanding how PTSD can impact on other psychological problems is an important area of future research, because it has important treatment implications. Targeting PTSD may have downstream benefits for many problems beyond the specific domain of that disorder.