Psychopathological intersection between obsessive-compulsive disorder and post-traumatic stress disorder: scoping review of similarities and differences

Abstract Introduction Although post-traumatic stress disorder and obsessive-compulsive disorder have distinct diagnostic criteria, some psychopathological phenomena seem to be shared, which may lead to misdiagnosis and erroneous treatment decisions. This scoping review explores the psychopathological similarities and differences between these two disorders. Method The review complies with the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and included articles published in Portuguese, English, or Spanish in the last 50 years indexed in the PubMed database. Case-reports were excluded. Results Fifty-three studies with different designs were included (30 [56.5%] were cross-sectional studies; eight [15.1%] were case-control studies; one [1.9%] was a cohort study; three [5.7%] were clinical trials; nine [17%] were reviews/systematic reviews; and two [3.8%] were meta-analyses). The main psychopathological aspects described by the studies included were flashbacks x obsessions; avoidant behavior (AB); depressive, anxious, and somatic symptoms; sexuality, sleep, and appetite; psychiatric comorbidities; and suicidality. The intersection between clinical features seems to occur in the extrinsic psychopathological dimension. Conclusion The disorders’ core psychopathological symptoms (intrinsic characteristics) are distinctly different, since flashbacks and obsessions are consequences of different predominant defective mental functions: the former derives from defective memory, the latter from defective thought. Along the same lines, the ABs observed in the two disorders are products of different purposes and inner necessities.


Introduction
Although post-traumatic stress disorder (PTSD) and obsessive-compulsive disorder (OCD) have distinct diagnostic criteria according to the DSM-5, 1 they seem to share some psychopathological phenomena, which could lead to misdiagnosis and, thus, to erroneous treatment decisions. 2For example, Green 3 reported that anxiety, insomnia, distressing and recurrent dreams, flashback imagery, intrusive thoughts, irritability, poor concentration, avoidant behavior (AB), and detachment were present for 70% of PTSD patients.While some of the abovementioned symptoms may also be present for OCD patients (anxiety, insomnia, intrusive thoughts, irritability, poor concentration, and ABs), others, such as flashbacks, are not always easily distinguished from obsessions.To make the comparison even more complex, patients with OCD report increased frequency and severity of stressful life events (SLE) (including traumatic events) in the 6 months prior to the onset of symptoms, 4 and close to 60% of OCD patients mention some SLE, making their occurrence a risk factor for comorbidity of PTSD with OCD. 5 Trying to understand the psychopathological overlap in PTSD-OCD comorbidity, Auxéméry 6 postulates that when PTSD patients re-experience, they become anxious; that hyper arousal increases anxious reactivity; and that avoidance strategies may increase anticipatory anxiety, reinforcing the existence of a "post-traumatic OCD" and also of many other "post-traumatic anxiety disorders."Rather than OCD, Freud would probably have used the term "obsessional neuroses," since after a traumatic event (such as, for example, a patient who heard from a fellow army officer a description of a Chinese torture method in which a large pot containing a live rat was strapped to the buttocks of the victim, and the rat, encouraged by a red-hot poker, would gnaw its way out through the victim's anus), patients would exacerbate some defense mechanisms, such as rationalization, doubt, undoing, and displacement. 7However, Lafleur et al. 8 did not find a relationship between the specific type of OCD symptoms exhibited and a history of psychologically traumatic events in children with OCD.It has also been argued that the severity of the traumatic event could predict obsessive-compulsive symptoms (OCS). 9More recently, after reporting that 19.1% of 1,001 OCD patients also had PTSD, Fontenelle et al. 10 elegantly proposed a continuum of distinct phenotypes of OCS in this context, ranging from pure OCD, passing through pre-traumatic OCD, post-traumatic OCD with previous OCS, and post-traumatic OCD without previous OCS, as can be seen in the adapted Figure 1. 10 On the other hand, other authors found no relation between traumatization or PTSD and OCD when compared to healthy controls. 119][20][21] However, unexpectedly, Shavitt et al. 22 found that OCD patients with PTSD exhibited a greater magnitude of response when compared with OCD patients without PTSD in specific OCD symptom dimensions.
Although other literature reviews have been carried out on this comorbidity, none has comprehensively explored the intersection between the psychopathological aspects of the two conditions, with a special focus on differentiating between symptoms that aid in differential diagnosis in a didactic manner.Thus, the main objective of this review is to explore the psychopathological similarities and differences between the two disorders, specifically comparing aspects such as flashbacks and obsessions; the occurrence of ABs; the presence of depressive, anxious, and somatic symptoms; sleep pattern; appetite; sexuality; psychiatric comorbidities, and suicidality, with the intention of providing a basis for future neurobiological and therapeutic studies.

Methods
This scoping review complies with the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 23 and was based on the following Boolean searches:

Results
Fifty-three studies with a variety of research

Discussion
Although only one paper directly compared OCD and PTSD patients, 37 most of the authors used one group of patients (OCD or PTSD) or "at-risk healthy subjects" to investigate the occurrence of symptoms (using validated instruments) specific to the other diagnostic group.
Thus, it was also necessary to select those papers to help to understand the scoping concepts considered as possible confounding issues in differential diagnosis between OCD and PTSD.

Flashbacks and obsessions
Although conceptually easy to distinguish, both phenomena share some features, which may, in fact, contribute to some patients finding it difficult to differentiate between them on self-report measures. 2lashbacks.Pierre Janet described how memories of traumatic experiences are dissociated from normal consciousness, resulting in powerful and uncontrollable re-enactments of the events. 61The most striking characteristics of this traumatic re-experiencing in PTSD are its involuntary and uncontrollable nature, the strong sensory impressions, and the sense of "nowness," or of the event occurring in the present. 31The DSM-5 and the proposed ICD-11 PTSD criteria have adopted a definition in which flashbacks are seen as existing along a continuum between extreme episodes (in which individuals even lose contact with their surrounding environment for periods of minutes or more) and any intrusive memories that are accompanied by a sense of reliving the event in the present. 1,31,62Some patients describe flashbacks as "a type of memory that you experience as markedly different from those memories of the event that you can retrieve at will, and in some cases, leading even to distorted time perception." 31rrently, there is enough evidence to support the position that flashbacks involve a perceptual memory system, which is distinct from ordinary episodic memory. 31While vivid memories are associated with additional activity in medial temporal lobe structures (such as the hippocampus), dual representation theory predicts that flashbacks may be associated with increased activity in motor areas and the insula and amygdala, but reduced activity in the medial temporal lobe. 31,63sessions.Esquirol described OCD as a disorder in which the sufferer is "chained to actions that neither reason nor emotion have originated, that conscience rejects, and will cannot suppress." 64Pierre Janet  Cross-sectional OCD (n = 278) CY-BOCS, Kiddie SADS-E (Epidemiological Version) Liu 41 Cross-sectional design with gene-environment interaction PTSD (n = 1,131) PCL-5 Lochner 19 Case-control OCD (n = 110) DES, CTQ  65 Rachman 64 postulates that obsessions are caused by catastrophic misinterpretations of the significance of one's unwanted intrusive thoughts.
Certain considerations are needed to fully understand the factors that precipitate intrusive thoughts and those linked to vulnerability to them. 667][68] Since it can be difficult to dissociate behavior and cognition in clinical practice (one leads to the other and vice-versa), we decided to describe all five circuits here, even when identifying that some circuits seem to be more behavioral (compulsive) than cognitive (obsessive).
Torres 56 Cross-sectional OCD (n = 955) DY-BOCS, Y-BOCS, SCID-I Torresan 57 Cross-sectional OCD (n = 858) DY-BOCS, SCID-I Unseld 58 Cross-sectional Adult cancer patients (n = 1,017) PTSS-10 Valderrama 59 Case-control OCD (n = 605) Wheaton 60 Randomized controlled trial  emotions (classic conditioning); in a second stage, the individual starts to avoid or rid themselves of the discomfort caused by the stimulus now conditioned.If performing the AB is followed by relief, the probability of repeating it increases (negative reinforcement or operant conditioning), [81][82][83] turning it into a possible mechanism of the association between trauma and obsession-compulsion. 40 According to the DSM-5, ABs are essential for a diagnosis of PTSD, but not for OCD. 1 Forbes et al. 33 postulated that requiring active avoidance helped to define the unique aspects of PTSD and reduced spurious diagnoses of PTSD in those with depression (reducing this comorbidity by 44%).Corroborating this, Liu et al. 41 described a relation between the serotonin transporter gene-linked polymorphic region (5-HTTLPR), interacting with trauma exposure to increase general risk for symptoms of PTSD, including ABs.Meanwhile, AB is described in almost 70% of OCD patients 60 and has been related to higher severity, to the contamination/cleaning subtype, and to a reduced probability of remission. 49us, it is unequivocal that AB may represent not only a structural, but also a learned psychopathological feature which interferes in the presentation and in the treatment response.For PTSD, the ABs seems to happen a posteriori (based on reasoning from known/real past traumatic facts or events rather than on assumptions or predictions), as an attempt to avoid triggering

Depressive symptoms
Depressive symptoms are prevalent in patients with OCD and in patients with PTSD. 1 Accordingly, major depressive disorder (MDD) is the most common comorbidity in OCD patients (up to 2/3 may experience a depressive episode during their lifetime). 1,84,85In PTSD, depressive symptoms are also quite common, since "negative mood" is part of the diagnostic criteria for this disorder (Criterion D in the DSM-5).It should be noted, however, that depressed mood in PTSD is associated with a traumatic event, but it can lead to distorted and negative cognitions in relation to the event, decreased interest in activities, and feelings of alienation or inability to feel positive emotions, 1 mimicking major depression and making differential diagnosis complex and difficult to accomplish. 86We can speculate that major depression in OCD may occur due to the severity, chronicity, or even the specific content of the obsessions, which may lead patients to feel low self-esteem, guilt, or shame, since the content of some obsessions are not morally or socially acceptable (e.g., sexual, aggressive, blasphemous).
Gershuny et al. 12 and Huppert et al. 37 hypothesized that, in addition to the intersection with psychopathological symptoms, depressive symptoms could be a mediating factor in this comorbidity, since the rate of diagnosis of PTSD was higher in patients with OCD who also suffered from depression. 35,37rroborating this hypothesis, in a study with 104 individuals who had this comorbidity, Merrill et al. 46 found that depressed patients had higher levels of OCS and greater severity of post-traumatic stress symptoms.
However, Morina et al. 9 found that only the severity of the posttraumatic stress symptoms was predictive of OCS, whereas number of traumatic life event types and depressive symptoms were not.How depression may interconnect PTSD and OCD, however, needs further investigation.

Anxious and somatic symptoms
As with depressive symptoms, there is also a high prevalence of anxiety in both OCD and PTSD.The association with OCD is so clear that in the DSM-III, III-R, and IV it was considered to be one of the anxiety disorders and these symptoms were considered key to syndromic diagnosis. 55Despite the change in DSM-5, many experts questioned the decision, considering that anxiety is indeed a central aspect of the clinical presentation of OCD. 1,42An association also occurs in PTSD, since evidence shows that people who experience the disorder are at higher risk of anxiety symptoms. 27,44en though the clinical presentation of PTSD can vary according to the severity of the symptoms and to the nature of the trauma experienced, anxiety is certainly a prevalent symptom.For example, 69% of the spouses of patients admitted to an intensive care unit (ICU) had clinically restricted anxiety. 87erach et al. 38 emphasize that fear of death is part of the anxiety spectrum, but can be considered as a transdiagnostic symptom since it is present in several mental disorders.While this fear can lead to safer behaviors and the search for a more meaningful life, when intense or excessive it causes extreme anxiety and leads to maladaptive behaviors. 43In OCD, the fear of dying can be clear in some cases, as in the contamination dimension, for example, the fear of dying or of causing death because of being contaminated is what motivates suffering and repetitive behaviors.The same occurs in the aggressiveness dimension, where the fear of death is central to repetition of symptoms.One example of this is when patients over-check the windows and doors of the home, for fear that a burglar will invade the home and put their lives at risk. 88,89Anxiety related to the fear of dying seems to be more prevalent in some specific dimensions, such as contamination, checking, and hoarding, or in patients with obsessive predominance. 44dour et al. 26 demonstrated that the intensity of peritraumatic self-focused disgust was significantly related to contamination-based OC symptoms while peritraumatic fear and other-focused disgust were related to posttraumatic stress symptoms.Menzies et al. 45 suggested in a study with 98 patients with OCD that the presence of fear of dying may increase the risk of comorbidity with anxiety disorders and influence the trajectory of the disorder.
In the clinical presentation of PTSD, autonomic and anxiety symptoms are also more the rule than the exception.Criterion B of DSM-5 mentions that there may be intrusive memories, distressing dreams or intense physiological reactions and Criterion E includes symptoms such as hypervigilance and exaggerated startle response. 1,44,90Such symptoms are clinically associated with anxiety, as well as with ABs that are also common in clinical practice and require special treatment in PTSD. 3 Since anxiety symptoms are part of both OCD and PTSD and can also be a comorbid disorder, regular symptom monitoring is important, requiring individualized investigation. 44,90 addition to the correlation with anxiety, associations between PTSD and somatic syndromes have been reported in the literature.Exposure to traumatic events seems to be associated with a higher prevalence of fibromyalgia, chronic pain, and chronic fatigue syndrome. 24,91The DSM-5 description of the disorder itself explains that dissociative symptoms and flashbacks are so prevalent in the clinical condition that they are part of the diagnostic criteria. 1In addition, somatic complaints such as headache, body aches, and gastrointestinal symptoms tend to be more intense in individuals with PTSD than in those without this diagnosis. 25However, Sikharulidze et al. 54 argue that this correlation is mediated by depressive and anxious symptoms, since it loses statistical significance when patients with PTSD are controlled for these symptoms.
Although some somatic obsessions may be present in OCD, the evidence of the relationship between OCD and somatic disorders is not robust as with PTSD.
Valderrama et al. 59 even described, for example, that when a somatic symptom or disorder (such as body dysmorphic disorder, for example) occurs with OCD, PTSD would probably also be present, making it a predictor of presence of BDD symptoms among OCD individuals who have experienced at least one lifetime traumatic event.The absence of evidence is interesting, since most patients with OCD (60-70%) have sensory phenomena, which consist of physical sensations -often aversive -that lead to compulsive behavior. 32This phenomenon has a somatic characteristic, considering that patients actually "feel" the discomfort, even without a real stimulus of the same intensity. 32,92Thus, sensory phenomena could be misdiagnosed as "somatization," but this seems not to occur.One possibility that could explain this is that, when a patient is diagnosed with OCD, clinicians may consider that somatization is part of the disorder and not a comorbidity.Feske 93 and Otte 75 speculate that somatization may also be mediated by depressive symptoms and be causally related to PTSD or OCD.
To further understand the relationship between anxiety and depression, Lee et al. 76 examined the factor structure of the combined items from the Beck Anxiety Inventory (BAI) and the Beck Depression Inventory-II (BDI-II) in a psychiatric outpatient population.They suggested that the symptoms could be grouped into five factors: somatic anxiety, cognitive depression, somatic depression, subjective anxiety, and autonomic anxiety. 76Along the same lines, extrapolating their results, but to better understand how depressive and anxious symptoms can present in PTSD and/or OD, we could conjecture (but based on clinical experience) that depressive and anxious symptoms could be grouped into cognitive, somatic, autonomic, behavioral (including AB), and emotional (subjective) subgroups, which could help us to distinguish these clusters in PTSD and OCD patients, as summarized in Table 3. Nonetheless, this phenomenological hypothesis requires appropriate future investigation.

Sexuality, appetite, sleep pattern
Obsessive compulsive disorder and PTSD may both interfere in sexuality, appetite, and sleep patterns.
Sexuality is often ignored in clinical practice because the therapeutic focus is on symptom reduction, but it has gained attention in the recent literature on the subject. 77vidence shows that individuals with OCD tend to suffer from more dysfunction and less sexual satisfaction than the general population, which contributes to worse quality of life. 78,79Many factors may be involved in this relationship, but Pozza et al. 92 pointed out that patients with the dimension of contamination or excessive sensitivity to disgust seem to be more prone to sexual inhibition, due to anxiety related to imaginary risks.In addition, the DSM-5 emphasizes that in the sexuality dimension, patients may present obsessions, mental images of sexual characteristics that cause suffering, which leads to a relationship with impaired sexuality. 1When depressive symptoms are associated with the condition, impairment of sexual quality of life is expected, since sexual symptoms also occur in MDD. 94D also seems to be associated with the compulsive sexual disorder proposed in the ICD-11, 62 which can also contribute to low sexual satisfaction. 95Evidence also points to higher levels of sexual dissatisfaction and dysfunction in PTSD patients. 96,97It is possible that when the traumatic PTSD event is of a sexual nature, this association is even more prevalent, considering that intrusive memories, flashbacks, and negative cognitions are causally related to the event, harming future relationships. 98havioral changes associated with eating occur in many disorders, most of the time causing higher rates of obesity or overweight.However, OCD does not appear to increase this risk, although evidence on the topic is still scarce. 99[102] It is also possible to speculate that weight gain, obesity, or metabolic syndrome may occur in PTSD or OCD as a consequence of psychopharmacological therapies, since most of the medicines used (antidepressants, mood stabilizers and antipsychotics) seem to increase appetite. 70leep disorders are prevalent in PTSD, but in addition to occurring after the traumatic event, they also seem to be considered predictive of development of the disorder. 52,101,102Like nightmares, insomnia seems to be an important symptom of PTSD, given that cognitive behavioral therapy aimed at reducing insomnia also reduces PTSD symptoms. 103OCD patients also present marked sleep impairment, with severity varying according to the severity of the clinical condition.The type of sleep impairment varies between patients, from reduction in total sleep time or sleep efficiency to delayed specific sleep phases and impairment seems more frequent in patients with more depressive symptoms. 104,105ychiatric comorbidities According to the American Psychiatric Association (APA), approximately 3.5% of American adults are affected by PTSD every year, and it is estimated that one in 11 will have a lifetime diagnosis of PTSD. 1,28,39The lifetime prevalence of OCD is estimated to be around 1.5%. 713][74] Since a psychiatric comorbidity may determine a specific psychopathological presentation and can influence the conventional treatment response, we present the most common comorbidities in PTSD and OCD in a comparison table (Table 4).As can be seen,
the most common groups of psychiatric comorbidities for both PTSD and OCD are affective disorders (almost 50 and 68%, respectively), anxiety disorders (almost 55 and 75%, respectively), and substance use/abuse/ dependence (almost 78 and 36%, respectively), 28,50,73,106 although prevalence rates differ between the two disorders.Differing values between studies for each disorder may reflect different methodological aspects and discrepancies between recruitment strategies employed at primary and tertiary services.For example, Torresan et al. 57 found some differences between male and female OCD patients concerning specific psychiatric comorbidities, including PTSD, which were related to female, but not to male gender.Similarly, other authors found higher prevalence of OCD in a specific population of veterans. 34,36,48It is worth stressing that comorbidity of PTSD with OCD increases the severity of OCD, especially the compulsions. 47

Suicidality
More than 50% of PTSD patients seem to present some lifetime aspect of suicidality: almost 40% report ideation, 9% have planned suicide, and 10% have attempted suicide since the traumatic event. 29,109,112most one-third attempt suicide more than once. 112though some may conjecture that this could be due to comorbid depression, a 2-year prospective analysis indicated that PTSD only at baseline was predictive of greater risk of suicide ideation and attempts than major depression disorder, 110,111 and even patients with residual PTSD symptoms or subclinical PTSD presentation seem to have greater risk for suicide ideation. 113Rojas et al. 113  of suicidality increased the risk, 14,51,115,116 whereas compulsions had a comparatively protective effect. 51us, both PTSD and OCD are strongly related to suicidality, although the reasons and risk factors may differ between the two disorders.Some authors seem to relate it to factors such as co-occurrence with major depression (and/or depressive symptoms), but others suggest that suicidality may be a psychological feature independently related to each of the disorders, constituting a transdiagnostic phenomenon. 116Since we can calculate a determination coefficient (r²), which is the proportion of the variance in the dependent variable that is predictable from the independent variable(s), we could use the results from some authors to try to describe how much of the severity of the disorders may contribute to suicidality severity.For example, as described by Liu et al. 117 in a sample from China, the correlation between the severities of PTSD and suicide was r = 0.46, indicating that 21% of the severity of PTSD contributes to the severity of suicidality.Similarly, in a sample from India, Dhyani et al. 118 observed that the correlation between the severities of OCD and suicide was 0.68, which indicates that the severity of OCD may contribute to 46% of the severity of suicidality.

Final considerations
Since PTSD and OCD are both prevalent and

"
Obsessive-Compulsive Disorder AND Post-Traumatic Stress Disorder," "Obsessive-Compulsive Disorder AND trauma," "obsession AND Post-Traumatic Stress Disorder," "obsession AND trauma," "obsession AND flashback," and "Obsessive-Compulsive Disorder AND flashback."The inclusion criteria were: journal articles published in Portuguese, English, or Spanish, in the last 50 years (1971-2021), indexed on the PubMed database, with abstracts available, and involving humans.Case-studies were excluded.Literature searches and selection were conducted by three researchers, two of them acting as independent and blinded reviewers (RR and JVBF).First, a search was conducted on the PubMed database.All articles and abstracts initially retrieved (n = 592) were analyzed and those that were appropriate were selected.Both reviewers used the same inclusion and exclusion criteria mentioned above and compared their results with one another.Any disagreements that occurred during the initial process of analysis and selection were resolved by a third researcher (YAF).While reading the full text of the remaining papers, the authors searched for the following: any definitions or psychopathological features of the terms "obsession" and "flashbacks"; presence and description of AB; any clinical aspect or mention of depressive, anxious, or somatic symptoms; any mention of specific features of sleep, appetite, or sexuality due to the core psychopathological aspects of the disorders (but not due to the treatment); the main psychiatric comorbidities of both disorders; and any descriptive aspect of suicidality.The references of the papers selected were also reviewed.The results of the search are illustrated in Figure 2. No restrictions were established for the references the authors used to help them formulate the discussion section.Table S1 (onlineonly supplementary material) lists details of the search results.

Figure 2 -
Figure 2 -Flowchart illustrating study selection according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) PDS (PosttraumaticStress Diagnostic Scale); DES (Dissociative experience scale); and CTQ or CTQ-SF (Childhood Trauma Questionnaire, full version or Short Form; and PCL-5: PTSD Checklist for DSM-5; 3) Non-specific instruments (used to diagnose or to confirm diagnoses): SCID-I (Structured Clinical Interview for DSM-IV Axis I disorders); and SADS (Schedule for Affective Disorders and Schizophrenia, adult or Kiddie forms; and other psychometric instruments: MFDS (Multidimensional Fear of Death Scale); C-LFDS (Collett-Lester Fear of Death Scale).The DY-BOCS was only used by Brazilian authors, and only one team of authors used the MFDS and C-LFDS (in three different papers).
share some psychopathological features (such as ABs, depressive, anxious, and somatic comorbid aspects, suicidality, psychiatric comorbidities, and interference with sexuality, appetite, and sleep patterns), it could be argued that they could share some common neurobiological aspects and belong to the same spectrum of disorders.However, the intersection of their characteristics seems to occur in the extrinsic psychopathological dimension.The core psychopathological symptoms (intrinsic characteristics) are distinctly different, since flashbacks and obsessions are consequences of different predominant defective mental functions: the former derives from defective memory, the latter from defective thought.In the same way, the ABs observed in each disorder are derived from different purposes and inner necessities.Comorbidity of PTSD and OCD needs further and adequate investigation since post-traumatic OCD with previous OCS and post-traumatic OCD without previous OCS may signal distinct neurobiological and/or genetic aspects.Some limitations of this scoping review derive from the fact that only one database was used and the search was limited to three publication languages.The scarcity of exploratory psychopathological studies including both disorders (no studies were found that compared PTSD, OCD, and PTSD+OCD groups, for example) restricted the availability of robust evidence to better describe other similar or distinct aspects of these disorders,

Table 1 -
Summary of the 53 studies selected for inclusion in the review

Table 4 -
Comparison of the main psychiatric comorbidities for PTSD and OCD