The 12-month prevalence for dissociative amnesia among adults in a small U.S. commu- nity study was 1.8% (1.0% for males; 2.6% for females).
Onset of generalized amnesia is usually sudden. Less is known about the onset of localized and selective amnesias because these amnesias are seldom evident, even to the individual.
Although overwhelming or intolerable events typically precede localized amnesia, its on- set may be delayed for hours, days, or longer.
Individuals may report multiple episodes of dissociative amnesia. A single episode may predispose to future episodes. In between episodes of amnesia, the individual may or may not appear to be acutely symptomatic. The duration of the forgotten events can range from minutes to decades. Some episodes of dissociative amnesia resolve rapidly (e.g., when the person is removed from combat or some other stressful situation), whereas other episodes persist for long periods of time. Some individuals may gradually recall the dis- sociated memories years later. Dissociative capacities may decline with age, but not al- ways. As the amnesia remits, there may be considerable distress, suicidal behavior, and symptoms of posttraumatic stress disorder (PTSD).
Dissociative amnesia has been observed in young children, adolescents, and adults.
Children may be the most difficult to evaluate because they often have difficulty under- standing questions about amnesia, and interviewers may find it difficult to formulate child- friendly questions about memory and amnesia. Observations of apparent dissociative am- nesia are often difficult to differentiate from inattention, absorption, anxiety, oppositional behavior, and learning disorders. Reports from several different sources (e.g., teacher, therapist, case worker) may be needed to diagnose amnesia in children.
Environmental. Single or repeated traumatic experiences (e.g., war, childhood maltreat- ment, natural disaster, internment in concentration camps, genocide) are common ante- cedents. Dissociative amnesia is more likely to occur with 1) a greater number of adverse childhood experiences, particularly physical and/ or sexual abuse, 2) interpersonal vio- lence; and 3) increased severity, frequency, and violence of the trauma.
Genetic and physiological. There are no genetic studies of dissociative amnesia. Stud- ies of dissociation report significant genetic and environmental factors in both clinical and nonclinical samples.
Course modifiers. Removal from the traumatic circumstances underlying the dissociative amnesia (e.g., combat) may bring about a rapid return of memory. The memory loss of indi- viduals with dissociative fugue may be particularly refractory. Onset of PTSD symptoms may decrease localized, selective, or systematized amnesia. The returning memory, however, may be experienced as ﬂashbacks that alternate with amnesia for the content of the ﬂashbacks.
In Asia, the Middle East, and Latin America, non-epileptic seizures and other functional neurological symptoms may accompany dissociative amnesia. In cultures with highly re- strictive social traditions, the precipitants of dissociative amnesia often do not involve frank trauma. Instead, the amnesia is preceded by severe psychological stresses or con- ﬂicts (e.g., marital conﬂict, other family disturbances, attachment problems, conﬂicts due to restriction or oppression).
Suicidal and other self-destructive behaviors are common in individuals with dissociative amnesia. Suicidal behavior may be a particular risk when the amnesia remits suddenly and overwhelms the individual with intolerable memories.
Functional Consequences of Dissociative Amnesia
The impairment of individuals with localized, selective, or systematized dissociative am- nesia ranges from limited to severe. Individuals with chronic generalized dissociative am- nesia usually have impairment in all aspects of functioning. Even when these individuals "re-learn" aspects of their life history, autobiographical memory remains very impaired.
Most become vocationally and interpersonally disabled.