Dissociative amnesia is a common psychiatric disorder among certain populations such as sex workers and drug abusers. Additionally, dissociative amnesia is more common in patients with other comorbid psychiatric illness such as depression and conversion disorder. Dissociative amnesia might be global or localized. The most common type is the localized loss of certain life events that are usually traumatic and unpleasant. The diagnosis of dissociative amnesia is based on the clinical evaluation of the patient and the DSM-5 criteria. Brain imaging showed some metabolic derangements, especially in the frontal and medial temporal lobes. Treatment includes psychotherapy, antidepressants, and drug-assisted interviews to help the patient recall the traumatic and most likely causative event of their amnesia.
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Image: “Sad?” By Martin Cooper. License: CC BY-SA 2.0


Overview

Dissociative amnesia can be defined as memory loss due to dissociation.

The most important causes of this dissociation to happen are trauma and stress. People who suffer from dissociative amnesia usually have loss of autobiographical memory and only certain past experiences are lost. Most commonly, the loss experiences are also the triggers of amnesia, i.e. memories of sexual abuse and rape for instance.

A severe form of dissociative amnesia that is also characterized by purposeful traveling away from one’s home and surroundings is known as dissociative fugue. A dissociative fugue can be also associated with complete loss of one’s identity and the creation of a completely new identity.

Epidemiology of Dissociative Amnesia

The exact prevalence of dissociative amnesia in the community is unknown, but all dissociative disorders collectively are identified in up to 1.7 % of the general community. Approximately 10 % of psychiatric inpatients are diagnosed with some form of dissociative disorders, usually dissociative amnesia.

Nowadays, it is believed that amnesia in this group of patients is due to dissociation. Dissociation is believed to happen due to a severe traumatic event, or an emotional stressor. The main risk factors for dissociative amnesia in the general population are drug abuse, alcoholism, female gender, a career in prostitution or being an exotic dancer. These kinds of behaviors are believed to put the subject at an increased likelihood of experiencing a traumatic event in life, i.e. rape for example, which can explain why dissociative amnesia is more common in these special populations.

Additionally, patients with conversion disorders are more likely to suffer from dissociative amnesia due to the similar pathogenesis, i.e. experiencing a severe stressor or trauma.

Clinical Features of Dissociative Amnesia

Dissociative amnesia can be localized or generalized:

Localized amnesia is defined as the failure to recall events during a certain period and is the most common type of dissociative amnesia.

On the other hand, generalized amnesia is characterized by the complete loss of one’s life history. Generalized amnesia might be associated with the loss of previous common-sense knowledge about the world, i.e. semantic amnesia, or the loss of well-learned skills, procedural amnesia.

Localized amnesia might be difficult to recognize because the onset is usually insidious and the amount of information lost might seem trivial at first. On the other hand, generalized amnesia is characterized by dramatic and sudden onset.

Generalized amnesia is more common in veterans and survivors of natural disastrous events, whereas, localized amnesia is more commonly seen in rape victims or victims of physical or emotional abuse. The sudden recall of the lost memories can overwhelm the patient and is associated with an increased risk of suicide.

Diagnostic Criteria for Dissociative Amnesia

The DSM-5 criteria for the diagnosis of dissociative amnesia consist of four main points.

The patient should be unable to recall autobiographical information that is usually of traumatic nature and that the patient is expected to remember and should recall easily.

The patient’s social, occupational or academic life should be affected by this impairment.

Alcohol abuse, drug dependency, partial complex seizures, transient global amnesia, or traumatic brain injuries should be reliably excluded.

And the final criterion is that dissociative amnesia should better fit the clinical picture of the patient compared to other psychiatric disorders such as posttraumatic stress disorder, acute stress disorder, somatization disorder, malingering, or dissociative identity disorder.

Patients with dissociative amnesia should be sub-classified into with fugue or without fugue depending on whether the patient shows fleeing behavior or not.

Brain Imaging in Dissociative Amnesia

The main goal of brain imaging in dissociative amnesia is to identify potential novel biomarkers, increase the certainty of the diagnosis and provide objective measures for research purposes. Brain imaging in patients with dissociative amnesia does not affect the treatment plan.

Positron emission tomography (PET) with glucose has shown decreased cerebral glucose metabolism in the anterior temporo-frontal regions in patients with dissociative amnesia. These brain regions are known to be related to autobiography memory recall.

Water-based PET scans were also used in patients with dissociative amnesia to study which brain regions are activated when previous life experiences are presented to the patient compared to healthy controls.

Healthy controls usually have right temporo-frontal activation whereas patients with dissociative amnesia show left temporo-frontal activation. This finding has been explained based on our current understanding of the lateralization of the human brain, i.e. the activation of the left hemispheric regions is suggestive of the neutral perception of the patient’s own experiences rather than perceiving them as his or her own memories.

The right inferior frontal regions and the right prefrontal cortex were also showing hypometabolism on glucose PET in patients with dissociative amnesia. Later, these same patients underwent magnetic resonance spectroscopy (MRS) brain imaging of the same regions and they were found to have an impairment in the GABA/Glutamate ratios in that same region.

This finding is very important and very recent as it can have implications for the treatment of dissociative amnesia and in helping these patients recall the lost events, i.e. it seems that dissociative amnesia is after all an inhibition/excitation imbalance disorder that is localized to certain cortical regions.

Treatment of Dissociative Amnesia

Medical treatment of dissociative amnesia largely relies on the management of the associated depression with antidepressants and the performance of drug-assisted interviews. Drug-assisted interviews with barbiturates or benzodiazepines can help in the retrieval of certainly lost memories that can be the trigger of the amnesia.

When the patient recalls certain traumatic events or memories, it should be noted that the risk of suicide increased significantly. Electroconvulsive therapy is either ineffective or harmful in dissociative amnesia. New approaches that are known to affect the inhibition/excitation balance in specific targeted brain regions such as transcranial direct current stimulation or transcranial magnetic stimulation are being tested as potential treatments for dissociative amnesia.

Hypnosis and hypnotherapy have shown some efficacy in helping the patients remember the traumatic events that led to this state. Psychotherapy should first aim to the stabilization of the patient and the reduction of the symptoms. The next step should be the identification of the causes of the dissociation and understanding that dissociation usually happens due to certain wrong ideation or thinking mechanisms, i.e. a rape victim might blame herself. Addressing these issues especially in group therapy has been shown to be helpful.

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