286 Trauma- and Stressor-Related Disorders
Dissociative disorders. Severe dissociative responses (i n the absence of characteristic
acute stress disorder symptoms) may be di agnosed as derealization/depersonalization
disorder. If severe amnesia of the trauma persists in the ab sence of characteristic acute
stress disorder symptoms, the diagnosis of  dissociative amnesia may be indicated.
Posttraumatic stress disorder. Acute stress disorder is dist inguished from PTSD because
the symptom pattern in acute stre ss disorder must occur within 1 month of the traumatic event
and resolve within that 1-month period. If th e symptoms persist for more than 1 month and
meet criteria for PTSD, the diagnosis is ch anged from acute stre ss disorder to PTSD.
Obsessive-compulsive disorder. In obsessive-compulsive diso rder, there are recurrent
intrusive thoughts, but these meet the definition  of an obsession. In addition, the intrusive
thoughts are not related to an experienced traumatic event, compulsions are usually pres-
ent, and other symptoms of acute st ress disorder are typically absent.
Psychotic disorders. Flashbacks in acute stress disorder  must be distinguished from il-
lusions, hallucinations, and other perceptual disturbances that may occur in schizophre-
nia, other psychotic disorders, depressive or  bipolar disorder with psychotic features, a
delirium, substance/medication -induced disorders, and psychotic disorders due to an-
other medical condition. Acut e stress disorder flashbacks ar e distinguished from these
other perceptual disturbances by being direct ly related to the traumatic experience and by
occurring in the absence of other psychotic or substance-induced features.
Traumatic brain injury. When a brain injury occurs in the context of a traumatic event
(e.g., traumatic accident, bomb blast, acceleration/deceleration trauma), symptoms of