Comorbid Posttraumatic Stress Disorder and Obsessive-Compulsive Disorder

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David Rhee

In the interest of transparency, I would first like to disclose my background and interest in posttraumatic stress disorder (PTSD) and obsessive-compulsive disorder (OCD) comorbidity. As a master’s-level intern in the clinical assessment team at the McLean Hospital’s Obsessive-Compulsive Disorder Institute (OCDI), I conduct diagnostic intake interviews that span the primary dimensions of the DSM-5 with a particular focus on conceptualizing patients’ obsessive-compulsive symptoms. Virtually all of the patients admitted for treatment at the OCDI present with moderate to severe OCD. According to Dr. Van Kirk, head of clinical assessment at the OCDI, about 55% of current patients at the OCDI endorse having experienced a traumatic event at some point in their life, while only around 10-15% of current patients meet criteria for a PTSD diagnosis. Currently within our field, the term ‘comorbidity’ is used in reference to cases where two or more illnesses are simultaneously present in a patient. This paper advances the perspective that, in some cases, comorbid OCD and PTSD interact in ways that are beyond merely additive, potentially resulting in important implications for treatment.

Both scientific research and clinical observations in the field of mental health support the idea that comorbid diagnoses in patients more often represent the rule rather than the exception. In particular, the extremely high rates of comorbidity linked to PTSD suggest that the diagnosis almost always develops in the context of other mental disorders such as Major Depressive Disorder (Koenen et al., 2008). Research has shown that OCD also disproportionately affects patients with PTSD. While the rate of OCD is 1% in the general population, approximately 30% of PTSD patients have either been previously diagnosed with OCD or develop symptoms that meet criteria for an OCD diagnosis within 12 months of receiving a PTSD diagnosis (Brown et al., 2001; Badour et al., 2012).

The OCDI administers Exposure and Response Prevention Therapy (ERP) as the evidence-based treatment of choice for patients with OCD (Hezel et al., 2019). In essence, ERP involves repeatedly exposing patients to their worst fears and anxiety triggers. Through coaching, patients gradually learn to control their compulsive responses, habituate to their triggers, and manage their anxiety in more adaptive ways. ERP takes a hands-on, head-first approach to recovery. For patients with a trauma history, and patients with treatment-resistant OCD in particular, evidence suggests that posttraumatic intrusions disrupt the effectiveness of the habituation process at the core of ERP (Shavitt et al., 2010; Dyskhoorn, 2014). Research and case studies also suggest the possibility that, for at least some patients with comorbid OCD and PTSD, a dynamic connection between symptoms of both disorders can exist, where treatments successful in reducing OCD symptoms inadvertently lead to an increase in PTSD symptoms, and vice-versa (Rachman,1991; Gershuny et al., 2003). Treatment that does not take into due consideration the interactions involved in comorbid PTSD and OCD diagnoses, such as whether a certain intrusive thought is better accounted for by a patient’s PTSD or OCD, has the potential to result in outcomes that project an illusion of progress without actually providing effective therapy.

Uncontrollable, intrusive thoughts that lead to distress and impairment comprise a hallmark symptom of both PTSD and OCD. Intrusive thoughts in OCD, or obsessions, are characterized by speculative thinking and excessive doubt regarding anxiety-provoking outcomes (APA, 2013). For example, patients with contamination OCD may feel severely distressed by the uncertainty over whether their hands may still be dirty despite excessive washing. Intrusive thoughts in PTSD, on the other hand, stem from a past traumatic event. Unlike OCD obsessions, intrusive thoughts in PTSD tend to reference back to a previous trauma, similar to other PTSD-related intrusive symptoms such as flashbacks or recurring nightmares.

Interplay between OCD and PTSD can occur when past traumatic experiences act as evidence to support the excessive labeling of otherwise improbable, speculative obsessions as threatening (Sasson et al., 2004). In addition to patients having access to experiential data for irrational fears, they are also being reminded either consciously or subconsciously of the event itself. Responsible practice must take into account that administering ERP to help a patient habituate to an obsession that causes traumatic re-experiencing is not the same as if that obsession was unrelated to trauma. When symptoms of PTSD surface in ERP treatment, clinicians are responsible for attending to the patient’s emotional processing and providing an immediate perception of safety.

Trauma exposure can lead to the formation of persistent and exaggerated negative cognitions (APA, 2013). These trauma-related cognitions will threaten, call into question, or sometimes completely shatter certain worldviews and core beliefs in relation to one’s sense of safety, self-worth, or trust in others. Often, traumatized individuals present with a heightened sense of responsibility and lowered sense of self-esteem due to these negative cognitions (Dykshoorn, 2014). While OCD obsessions trigger fear and anxiety through similar schemas concerning safety or self-worth, most patients with OCD possess fair to good insight over their symptoms (APA, 2013). When a patient shakes with mortal fear at the prospect of touching a dirty doorknob, clinicians may opt to dismiss their fears as unrealistic or imaginary. The majority of patients would agree, despite being unable to dismiss their fears with the same ease, as the DSM-5 suggests that only around 4% of patients with OCD present with absent insight or delusional beliefs (APA, 2013). It has also been suggested that patients with OCD possess an exaggerated sense of personal responsibility for their obsessions (Gershuny et al., 2002). Some may equate the mere thought of performing a taboo action to be the same as performing it. Others may feel personally responsible for performing a ritual in order to prevent disaster from befalling their loved ones. Unlike trauma-related cognitions, OCD obsessions are more likely to be associated with a compulsion.

OCD compulsions are ritualistic, often repetitive behaviors aimed at subduing the anxiety caused by obsessions. Some compulsions may be directly connected to the underlying fear, as with hand-washing rituals and contamination obsessions. In other cases, they may only be loosely related or not at all, such as with patients who feel that they must count, pace, or clap a certain amount of times to protect loved ones from unrelated disasters. Rather than adopting compulsions or rituals, patients with PTSD are more likely to develop hypervigilance and avoidance symptoms (APA, 2013). Both compulsions and hypervigilance behaviors provide a sense of safety to the patient upon completion, reducing their anxiety. In some cases, hypervigilance behaviors can overlap with certain compulsions, such as checking behaviors involving locks, windows, or perimeters. To outside observers, both compulsive and hypervigilant behaviors may be interpreted as excessive, ritualistic, or irrational. The main difference, however, is that hypervigilant behaviors, like trauma-related cognitions, stem from trauma and serve the perceived function of preventing the trauma from reoccurring, regardless of whether the threat has passed or how likely the event is to repeat itself (Rachman, 1991). The interpretation of cognitions and obsessions is a complex process that involves metaphorical and associative thinking as much as, or perhaps even more than, logic.

Although case studies certainly cannot serve as complete scientific evidence, consider the following synopsis of a patient presented by Gershuny et al. (2003) that may help illustrate the aforementioned concepts: Ms. A., a patient with severe PTSD and OCD, obsesses over the unlucky number ‘54,’ the age at which her stepmother was murdered by her father. Though even the patient herself is able to acknowledge that her preoccupation with the number ‘54’ is superstitious and irrational, clinicians’ attempts to expose Ms. A to the number ‘54’ elicited trauma-related fears and cognitions including “I am in danger,” “I am not in control,” and “someone who was supposed to take care of me was capable of murder.” Over the course of ERP treatment, Ms. A. developed more depressive symptoms and reported increased severity of trauma-related intrusions, numbing, social withdrawal, and avoidance behavior. Gershuny noted that, while her obsessions and rituals appeared to decrease initially, they re-intensified in frequency and duration following treatment. While this case study should be taken into consideration as mostly anecdotal evidence, Ms. A. serves as an example of a treatment-resistant patient who could potentially benefit from further inquiry into the effects of traumatic intrusions on the success of ERP therapy.

Although the primary scope of the present article involved OCD and PTSD comorbidity, complex interactions between mental illnesses are not limited to only these two diagnoses. Particularly, one area of interest for further research may be interactions between Borderline Personality Disorder, PTSD, and OCD (particularly Relationship-OCD). Another area of interest may be concerning the effects of Major Depressive Disorder on PTSD treatment outcomes in terms of potentially increased rates of suicidality and treatment dropout.

When PTSD exists in tandem with other diagnoses such as OCD, clinical pictures can vary in dynamic and complex ways that one line of secondary diagnosis cannot sufficiently reflect. Taken in light of the clinical implications that comorbidity can have on patients’ healing, new methods of conceptualizing trauma are necessary. In order to provide effective and responsible care for patients, clinicians are encouraged to strive for relationships that yield information beyond the manualized definitions of diagnostic criteria. Creating change on an institutional level can be arduous and slow, but pushing the limits of individual competence is an actionable endeavor upon which all clinicians in the field have the ability to act.


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David Rhee is a 2nd-year candidate for a Master’s degree in Mental Health Counseling at Boston College. He currently works as a clinical assessment intern at the Obsessive-Compulsive Disorder Institute at McLean Hospital in Belmont, Massachusetts. His primary interests within the field involve topics surrounding trauma, OCD, Asian-American issues, narrative therapy, qualitative research methods, and refugee mental health.