Dissociative Amnesia

The main symptom of dissociative amnesia is memory loss that is inconsistent with normal forgetfulness. The amnesia may be for a discrete period of time, for certain types of experiences, or for large portions of childhood.

Localized amnesia involves being unable to recall the events that occurred during 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 1 or more episodes of memory loss.

Selective amnesia involves forgetting some, but not all, of the events within a certain time period, or forgetting only part of a traumatic event.

In generalized amnesia, patients forget their identity and life history—eg, who they are, where they went, to whom they spoke, and what they did, said, thought, experienced, and felt during a substantial period of time. 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 others experiencing extreme trauma, 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.

Rarely, dissociative amnesia is accompanied by purposeful travel or bewildered wandering, called fugue (from the Latin word fugere "to flee").

Patients may experience multiple types of dissociative amnesia, especially in the face of cumulative trauma (1).

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 markedly distressed; others are indifferent. If those who are unaware of their amnesia present for psychiatric help, they may do so for other reasons.

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.

Patients have difficulty forming and maintaining relationships.

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.

• Psychiatric assessment, based on Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) criteria

• Psychiatric assessment and general medical examination to exclude other causes

• MRI, electroencephalography, and toxicology

Diagnosis of dissociative amnesia is clinical, based on presence of the following criteria in the DSM-5-TR (1):

• Patients' inability to recall important personal information (usually trauma- or stress-related) is not consistent with normal forgetfulness.

• Symptoms cause significant distress or significantly impair social or occupational functioning.

Also, the symptoms cannot be better accounted for by the effects of a medication or another disorder (eg, dementia, partial complex seizures, substance use disorder, traumatic brain injury, posttraumatic stress disorder, another dissociative disorder).

Diagnosis requires a medical and psychiatric examination to exclude other possible causes. Initial evaluation should include

• MRI to identify reduced volume of the hippocampal CA1 region and/or other structural causes

• Electroencephalography (EEG) to exclude a seizure disorder

• Blood and urine tests to exclude toxic causes, such as illicit drug use

Psychological testing can help better characterize the nature of the dissociative experiences.

• To recover memory, a supportive environment and sometimes hypnosis or a medication-induced semihypnotic state

• Psychotherapy to deal with issues associated with recovered memories of traumatic or stressful events

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 of 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 a supportive environment does not result in improvement or when the need to recover memories is urgent, questioning patients while they are under hypnosis or, rarely, in a medication-induced (barbiturate or benzodiazepine) semihypnotic state can be successful (1). These strategies must be used 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:

• Giving meaning to the underlying trauma or conflict, including resolving inappropriate guilt

• Resolving problems associated with the amnestic episode

• Enabling patients to move on with their life

If patients have experienced dissociative fugue, psychotherapy, sometimes combined with hypnosis or medication-facilitated interviews, may be used to try to restore memory; these efforts are not always successful. Regardless, psychotherapy may be useful for patients to 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.

Sometimes memories return quickly, as can happen when patients are taken out of the traumatic or stressful situation (eg, combat, sexual assault). 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 (1).

The prognosis is determined mainly by the following:

• The patient’s life circumstances, particularly stresses and conflicts associated with the amnesia

• The patient’s overall psychological adjustment