Dissociative amnesia is inability to recall important personal information that is too extensive to be explained by normal forgetfulness. Diagnosis is based on history after ruling out other causes of amnesia. Treatment is psychotherapy, sometimes combined with hypnosis or drug-facilitated interviews.
The information lost would normally be part of conscious awareness and would be described as autobiographic memory—eg, the story of one's life: who one is, where one went, to whom one spoke, and what one did, said, thought, experienced, and felt. Although the forgotten information may be inaccessible to consciousness, it sometimes continues to influence behavior.
Dissociative amnesia is likely underdetected. Prevalence, although not well-established, has been estimated at 2 to 6% in the general population. Dissociative amnesia is most commonly diagnosed in young adults. The amnesia appears to be caused by traumatic or stressful experiences endured or witnessed (eg, physical or sexual abuse, rape, combat, abandonment during natural disasters, death of a loved one, financial troubles) or by tremendous internal conflict (eg, turmoil over guilt-ridden impulses, apparently unresolvable interpersonal difficulties, criminal behaviors).
Symptoms and Signs
The main symptom is memory loss, usually of information regarding traumatic or stressful events or entire periods of the patient's life. Characteristically, patients experience one or more episodes in which they forget some or all of the events that occurred during a period of time. These periods, or gaps in memory, may represent only a few hours or can encompass years. Usually, the forgotten period of time is clearly demarcated.
Patients seen shortly after they become amnestic may appear confused. Some are very distressed; others are indifferent. Some, especially if the amnesia is for the remote past, may not even be aware of it, and if they present for psychiatric help, the presenting complaint is often different.
Diagnosis requires a medical and psychiatric examination. Initial evaluation should include MRI to rule out structural causes, EEG to rule out a seizure disorder, and blood and urine tests to rule out toxic causes, such as illicit drug use. Psychologic testing can help better characterize the nature of the dissociative experiences.
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 patient's life circumstances, particularly stresses and conflicts associated with the amnesia, and by the patient's overall mental adjustment.
If memory of only a very short time period is lost, supportive treatment 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 also must carefully phrase questions so as not to suggest the existence of an event and risk creating a false memory. 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 narrative. Once the amnesia is lifted, treatment helps with the following:
Last full review/revision June 2008 by Daphne Simeon, MD
Content last modified February 2012