Kaplan & Sadock’s Pocket Handbook of Clinical Psychiatry

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Epidemiology Of all the dissociative disorders, dissociative amnesia is the most common, with a 12-month prevalence of approximately 2%. It is far more common in women than men, occurs more often in adolescents and young adults than in older adults, and increases in incidence in the wake of natural disasters and wars. Comorbidity Common comorbidities of dissociative amnesia include posttraumatic stress dis order (PTSD), somatic symptom disorder, conversion disorder, and dependent or avoidant personality disorders. Etiology Dissociative amnesia typically occurs following extreme emotional trauma, par ticularly in the wake of physical or sexual abuse. Dissociative amnesia can also occur following traumatic brain injury (TBI) in the absence of emotional trauma. Laboratory and psychological tests There are no laboratory tests for dissociative amnesia, though blood and urine tests can be useful to rule out the use of substances that may have caused the am nesia. Patient responses during a clinical evaluation will oftentimes be sufficient for a diagnosis (see Table 16-2 ). Pathophysiology Tonic immobility, a rigid state of paralysis that is often associated with the opos sum (ie, “playing possum”), is a response to stress that appears to be closely associated with dissociative amnesia. When the body is in this unresponsive state, it may result in reduced neural network activity, including connectivity between the hippocampus and neocortical areas, thereby resulting in memory fragmentation. Tests involving functional magnetic resonance imaging (fMRI) in patients with dissociative amnesia have shown reduced hippocampal activity and increased activity in the prefrontal cortex while testing for recall. Diagnosis, signs, and symptoms Patients who suffer from dissociative amnesia have an inability to recall vital autobiographical details of an event. The DSM-5-TR diagnostic criteria for dis sociative amnesia note that the forgotten information is usually of a traumatic or stressful nature but does not require it (see Table 16-3 ). Dissociative amnesia TABLE 16-1. Types of Dissociative Amnesia Localized amnesia: Inability to recall events related to a circumscribed period of time Selective amnesia: Ability to remember some, but not all, of the events occurring during a circum scribed period of time Generalized amnesia: Failure to recall one’s entire life Continuous amnesia: Failure to recall successive events as they occur Systematized amnesia: Failure to remember a category of information, such as all memories relating to one’s family or to a particular person

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