(See also Overview of Dissociative Disorders.)
In dissociative amnesia, the information lost would normally be part of conscious awareness and would be described as autobiographic memory.
Although the forgotten information may be inaccessible to consciousness, it sometimes continues to influence behavior (eg, a woman who was raped in an elevator refuses to ride in elevators even though she cannot recall the rape).
Dissociative amnesia is probably underdetected. Prevalence is not well-established; in one small US community study, the 12-month prevalence was 1.8% (1% in men; 2.6% in women).
The amnesia appears to be caused by traumatic or stressful experiences endured or witnessed (eg, physical or sexual abuse, rape, combat, genocide, natural disasters, death of a loved one, serious financial troubles) or by tremendous internal conflict (eg, turmoil over guilt-ridden impulses or actions, apparently unresolvable interpersonal difficulties, criminal behaviors).
The main symptom of dissociative amnesia is memory loss that is inconsistent with normal forgetfulness. The amnesia may be
Rarely, dissociative amnesia is accompanied by purposeful travel or bewildered wandering, called fugue (from the Latin word fugere "to flee").
Localized amnesia involves being unable to recall a specific event or events or a specific period of time; these gaps in memory are usually related to trauma or stress. For example, patients may forget the months or years of being abused as a child or the days spent in intense combat. The amnesia may not manifest for hours, days, or longer after the traumatic period. Usually, the forgotten time period, which can range from minutes to decades, is clearly demarcated. Typically, patients experience one or more episodes of memory loss.
Selective amnesia involves forgetting only some of the events during a certain period of time or only part of a traumatic event. Patients may have both localized and selective amnesia.
In generalized amnesia, patients forget their identify and life history—eg, who they are, where they went, to whom they spoke, and what they did, said, thought, experienced, and felt. Some patients can no longer access well-learned skills and lose formerly known information about the world. Generalized dissociative amnesia is rare; it is more common among combat veterans, people who have been sexually assaulted, and people experiencing extreme stress or conflict. Onset is usually sudden.
In systematized amnesia, patients forget information in a specific category, such as all information about a particular person or about their family.
In continuous amnesia, patients forget each new event as it occurs.
Most patients are partly or completely unaware that they have gaps in their memory. They become aware only when personal identity is lost or when circumstances make them aware—eg, when others tell them or ask them about events they cannot remember.
Patients seen shortly after they become amnestic may appear confused. Some are very distressed; others are indifferent. If those who are unaware of their amnesia present for psychiatric help, they may do so for other reasons.
Patients have difficulty forming and maintaining relationships.
Some patients report flashbacks, as occur in posttraumatic stress disorder (PTSD); flashbacks may alternate with amnesia for the contents of the flashbacks. Some patients develop PTSD later, especially when they become aware of the traumatic or stressful events that triggered their amnesia.
Depressive and functional neurologic symptoms are common, as are suicidal and other self-destructive behaviors. Risk of suicidal behaviors may be increased when amnesia resolves suddenly and patients are overwhelmed by the traumatic memories.
Dissociative fugue is an uncommon phenomenon that sometimes occurs in dissociative amnesia.
Dissociative fugue often manifests as
Patients, having lost their customary identity, leave their family and job. A fugue may last from hours to months, occasionally longer. If the fugue is brief, they may appear simply to have missed some work or come home late. If the fugue lasts several days or longer, they may travel far from home, assume a new name and identity, and begin a new job, unaware of any change in their life.
Many fugues appear to represent disguised wish fulfillment or the only permissible way to escape from severe distress or embarrassment, especially for people with a rigid conscience. For example, a financially distressed executive leaves a hectic life and lives as a farm hand in the country.
During the fugue, patients may appear and act normal or only mildly confused. However, when the fugue ends, patients report suddenly finding themselves in the new situation with no memory of how they came to be there or what they have been doing. They often feel shame, discomfort, grief, and/or depression. Some are frightened, especially if they cannot remember what happened during the fugue. These manifestations may bring them to the attention of medical or legal authorities. Most people eventually recall their past identity and life, although recalling may be a lengthy process; a very few remember nothing or almost nothing about their past indefinitely.
Often, a fugue state is not diagnosed until patients abruptly return to their pre-fugue identity and are distressed to find themselves in unfamiliar circumstances. The diagnosis is usually made retrospectively, based on documentation of the circumstances before travel, the travel itself, and the establishment of an alternate life.
Diagnosis of dissociative amnesia is clinical, based on presence of the following criteria in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5):
Also, the symptoms cannot be better accounted for by the effects of a drug or another disorder (eg, partial complex seizures, substance abuse, traumatic brain injury, posttraumatic stress disorder, another dissociative disorder).
Diagnosis requires a medical and psychiatric examination to rule out other possible causes. Initial evaluation should include
Psychologic testing can help better characterize the nature of the dissociative experiences.
Sometimes memories return quickly, as can happen when patients are taken out of the traumatic or stressful situation (eg, combat). In other cases, amnesia, particularly in patients with dissociative fugue, persists for a long time. The capacity for dissociation may decrease with age.
Most patients recover their missing memories, and amnesia resolves. However, some are never able to reconstruct their missing past.
The prognosis is determined mainly by the following:
If memory of only a very short time period is lost, supportive treatment of dissociative amnesia is usually adequate, especially if patients have no apparent need to recover the memory of some painful event.
Treatment for more severe memory loss begins with creation of a safe and supportive environment. This measure alone frequently leads to gradual recovery of missing memories. When it does not or when the need to recover memories is urgent, questioning patients while they are under hypnosis or, rarely, in a drug-induced (barbiturate or benzodiazepine) semihypnotic state can be successful. These strategies must be done gently because the traumatic circumstances that stimulated memory loss are likely to be recalled and to be very upsetting. The questioner must carefully phrase questions so as not to suggest the existence of an event and risk creating a false memory. Patients who were abused, especially during childhood, are likely to expect therapists to exploit or abuse them and to impose uncomfortable memories rather than help them recall real memories (traumatic transference).
The accuracy of memories recovered with such strategies can be determined only by external corroboration. However, regardless of the degree of historical accuracy, filling in the gap as much as possible is often therapeutically useful in restoring continuity to the patient’s identity and sense of self and in creating a cohesive life narrative.
Once the amnesia is lifted, treatment helps with the following:
If patients have experienced dissociative fugue, psychotherapy, sometimes combined with hypnosis or drug-facilitated interviews, may be used to try to restore memory; these efforts are not always successful. Regardless, a psychiatrist can help patients explore how they handle the types of situations, conflicts, and emotions that precipitated the fugue and thus develop better responses to those events and help prevent fugue from recurring.