The clinical expression of PTSD can vary significantly in terms of severity. Although the diagnosis is categorical, there is evidence of a dimensional structure to PTSD (Broman-Fulks et al., 2006; Forbes, Haslam, Williams, & Creamer, 2005; Ruscio, Ruscio, & Keane, 2002). An implication of this dimensional structure is that milder symptoms of PTSD may cause significant distress and impairment. Indeed, one study found that veterans with subthreshold PTSD underutilize mental health care, despite increased psychiatric comorbidity and impairment relative to veterans without PTSD (Grubaugh et al., 2005). Yet other studies using samples of Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF) veterans have found an association between subthreshold PTSD and elevated levels of anger and hostility, physical health functioning, and an increased likelihood of hopelessness and suicidal ideation relative to those without PTSD (Jakupcak et al., 2011). Among civilians, subthreshold PTSD has likewise been associated with levels of impairment and suicidality that are equivalent to those with full PTSD (Zlotnick, Franklin, & Zimmerman, 2002).

Suicidality is elevated among individuals with PTSD (Panagioti, Gooding, & Tarrier, 2009; Jakupcak et al., 2011), and particular types of trauma, such as childhood abuse, military sexual trauma, and combat, may be more strongly associated with suicidality than others (Afifi et al., 2008; Kimerling, Gima, Smith, Street, & Frayne, 2007). Additionally, increased risk of suicidality is uniquely associated with PTSD (Sareen, Houlahan, Cox, & Asmundson, 2005; Sareen et al., 2007). That is, this association is not solely accounted for by the presence of other psychiatric conditions commonly found with PTSD. Of course, an increased risk of suicidality is present in a number of other psychiatric conditions to a comparable or greater degree than that found in PTSD (Nock, Hwang, Sampson, & Kessler, 2010).

The clinical picture of acute stress disorder (ASD) is similar to that of PTSD. Additionally, a review on the topic found that at least half of trauma survivors with ASD subsequently met criteria for PTSD (Bryant, Friedman, Spiegel, Ursano, & Starin, 2011). This finding suggests that individuals with ASD are, in fact, at higher risk of subsequently developing PTSD. Conversely, however, the majority of individuals who subsequently develop PTSD do not initially meet criteria for ASD, suggesting that ASD (using DSM-IV criteria) is not highly specific with regard to its predictive utility. Additional findings suggest that the predictive power of ASD is increased when subthreshold symptoms are used and the dissociative symptoms required for DSM-IV are relaxed (Bryant et al., 2011). These and similar findings likely influenced the decreased emphasis in DSM-5 on dissociation symptoms in favor of accepting a broader symptom presentation and one that more closely mirrors the symptoms associated with PTSD.

Due to the conceptualization of adjustment disorders as fairly time limited, as well as their history as a nebulous, catch-all diagnostic category, they have not been well studied in the psychiatric literature. The findings that do exist largely consist of non-U.S. samples, focus on children or adolescents, and/or were published in the 1980s and early 1990s. Some commonly agreed upon emotional signs of adjustment disorders are sadness, hopelessness, lack of enjoyment, crying spells, nervousness, anxiety, worry, trouble sleeping, difficulty concentrating, feeling overwhelmed, and thoughts of suicide. Some behavioral signs of adjustment disorders include fighting, reckless behaviors, neglecting important tasks or responsibilities, and avoiding family or friends. Although the presence of an adjustment disorder has been linked to increased suicidal ideation and risk of suicide (e.g., Portzky, Audenaert, & Vanheeringen, 2005; Taggart et al., 2006), they are often considered less severe than other psychiatric disorders. Supporting this view, one study found that adjustment disorders range in severity between no psychiatric disorder and the presence of a mood or anxiety disorder (Fernandez et al., 2012).

Comorbidity is a concern when diagnosing PTSD. Large nationally representative samples have found that PTSD is significantly correlated with the majority of mood and anxiety disorders, as well as alcohol use disorders (National Comorbidity Survey Replication [NCS-R]; Kessler, Chiu, Demler, & Walters, 2005; National Comorbidity Survey [NCS]; Kessler, Sonnega, Bromet, Hughes, & Nelson, 1995). Data from the NCS-R found that approximately half of those who met criteria for PTSD also met criteria for at least three additional psychiatric diagnoses (Kessler et al., 1995). Although there is some degree of symptom overlap between PTSD and other psychiatric diagnoses (e.g., sleep and concentration difficulties and diminished interest in activities are common to both depression and PTSD), this overlap does not account for the high rate of comorbidity (Elhai, Grubaugh, Kashdan, & Frueh, 2008). When comorbid with mood disorders, PTSD is more likely to be primary, whereas it is more likely to be secondary when comorbid with anxiety disorders (Kessler et al., 1995). Importantly, PTSD and comorbid diagnoses may change over time within a given individual. A study of trauma survivors found that half of those who reported PTSD only at 3-month follow-up reported depression only at 12-month follow-up; likewise, half of those with depression only at 3-month follow-up reported PTSD only at 12-month follow-up (O’Donnell, Creamer, & Pattison, 2004).

Due to the lack of epidemiological studies specific to ASD or the adjustment disorders, there are few reliable data on the clinical comorbidity associated with these disorders. Given the conceptual overlap between ASD and PTSD, it is likely that individuals with ASD experience high rates of mood, anxiety, and substance disorders relative to the general population, as well as an increased risk of suicidality. As noted elsewhere, adjustment disorders in the DSM-IV served as a residual “catch-all” diagnostic category once other psychiatric conditions were ruled out. As such, they are seldom diagnosed with other psychiatric conditions. With this restriction in mind, adjustment disorders have most often been linked in adult samples to a comorbid diagnosis of a personality disorder, substance use disorder, and increased suicidality (Dowrick et al., 1998; Greenberg, Rosenfeld, & Ortega, 1995; Polyakova, Knobler, Ambrumova, & Lerner, 1998; Strain et al., 1998).

In the general population, the 12-month and lifetime prevalence of PTSD is 3.5 and 6.8%, respectively (Kessler, Burglund, Demler, et al., 2005; Kessler et al., 2005). Point prevalence of PTSD among U.S. combat veterans is estimated to be between 2% and 17%, depending on the characteristics of the sample and the measurement strategies that were used (Richardson, Frueh, & Acierno, 2010). There are different conditional probabilities of developing PTSD by trauma type. For example, combat exposure and physical and sexual abuse are more often associated with PTSD than other types of trauma. Despite this variability, the symptom expression of PTSD remains fairly consistent regardless of the type of trauma experienced.

Little is known regarding the prevalence of ASD and the adjustment disorders in the general population. Large-scale epidemiological studies, such as the World Health Organization (WHO) Mental Health Epidemiologic Survey, the Epidemiologic Catchment Area study, and the National Comorbidity Survey Replication, did not report on these disorders. Rates of ASD in community and clinical samples range from 7% to as high as 28% with a mean rate of 13% (Bryant et al., 2011), and rates of ASD are typically higher among victims of violent versus nonviolent traumas. When subsyndromal cases of ASD are included, estimates of the disorder increase from 10% to 32% with a mean rate of 23% (Bryant et al., 2011).

There are few reliable findings on the prevalence of adjustment disorders. This gap in knowledge is likely influenced by the poor delineation between adjustment disorders and normal or adaptive stress responses, as well as the use of adjustment disorders as a residual “last resort” diagnostic category in the DSM-IV. One epidemiological study, the European Outcome of Depression International Network, found a 1% prevalence of adjustment disorder with depressed mood (ODIN; Ayuso-Mateos et al., 2001). More circumscribed samples of adults suggest adjustment disorders are more common in hospital psychiatric consultation settings (12%; Strain et al., 1998; 18.5%; Foster & Oxman, 1994) and among psychiatric inpatient admissions (Koran et al., 2002). A recent meta-analysis found prevalence rates of 15.4% and 19.4% in palliative care and oncology settings, respectively (Mitchell et al., 2011).

There are a number of diagnostic measures for assessing PTSD.

Although revisions are underway, these measures reflect DSM-IV, rather than DSM-5, criteria for PTSD. The Clinician-Administered PTSD Scale (CAPS; Weathers, Keane, & Davidson, 2001) is the most common interviewer-based instrument for PTSD and has robust psychometric properties (Weathers et al., 2001). The CAPS includes a detailed assessment of each traumatic event, frequency and severity ratings for each symptom, and overall distress and impairment ratings. Several CAPS scoring algorithms have demonstrated good diagnostic utility (Weathers, Ruscio, & Keane, 1999). A common scoring method is to score a symptom as present if the frequency is greater than or equal to 1 and the intensity is greater than or equal to 2, and to further require the endorsement of a sufficient number of symptoms for each symptom cluster. This method favors sensitivity (0.91) over specificity (0.71), and thus may be better for screening purposes. Using a total dimensional cut-score of greater than or equal to 65, on the other hand, favors specificity (0.91) over sensitivity (0.82), and thus may be better for confirming a diagnosis (Weathers et al., 1999). Other interview measures include the PTSD Symptom Scale–Interview (PSS-I; Foa & Tolin, 2000) and the Structured Interview for PTSD (SI-PTSD; Davison, Smith, & Kudler, 1989). Additionally, the Structured Clinical Interview for DSM-IV (SCID-IV; First, Spitzer, Gibbon, & Williams, 1996) and the Anxiety Disorders Interview Schedule (ADIS-IV; Brown, Di Nardo, & Barlow, 1994) contain a module for assessing the presence or absence of PTSD.

A number of causal mechanisms have been implicated in the development of PTSD. These include genetic factors, brain structure and neurochemical abnormalities, pre- and post-trauma life events, cognitive appraisals and attentional biases, and sociodemographic variables such as gender.