Dissociative amnesia is a condition in which retrograde memory loss occurs, usually involving a specific period of time. Emotional trauma is thought to be the primary cause, whereas numerous other factors have been implicated in its pathogenesis. The diagnosis is confirmed once all other potential causes of memory loss (drugs, organic diseases) have been excluded. Psychotherapy is the main therapeutic modality.
The clinical presentation of patients with dissociative amnesia can significantly vary. Mental status may be completely normal, but confusion and the presence of other dissociative disorders, such as personality changes, are not uncommon . In terms of memory loss, pure retrograde amnesia is identified in most cases and primarily involves episodic-autobiographic memories . Some individuals may not be aware of memory loss, while rare cases have described loss of both semantic and functional memories that can impair normal daily activities , which should be recognized by the physician either during patient history or physical examination.
Patient history is the single most important part of the diagnostic workup, since a careful and gentle approach to the patient may reveal key information regarding memory loss and its onset. It is important to establish the absence of anterograde amnesia, which is rarely present in patients with dissociative amnesia . Before making the diagnosis, other organic conditions that present with similar complaints need to be excluded. Prior physical trauma to the temporal lobe or the hippocampus, seizures and drug abuse should be included in the differential diagnosis. Blood and urine toxicology tests should be done, together with imaging studies including CT or MRI to exclude trauma. EEG is necessary to perform in order to rule out seizures . Studies have confirmed that functional brain imaging such as PET scanning shows reduced glucose uptake in various regions, such as the inferolateral prefrontal cortex, which is known to be the site where retrieval of autobiographical memories occurs .
Depending on the severity of memory loss, various therapeutic measures should be implemented. Ensuring a safe, supportive and pleasant environment for patients who experience severe emotional trauma is the first step in treatment and is often sufficient for milder cases . Drug-induced hypnosis using benzodiazepines or barbiturates have shown to be effective in a subset of patients , but psychotherapy is considered to be the mainstay of managing both mild and severe forms of amnesia . Cognitive behavioral therapy (CBT) and acceptance and commitment therapy (ACT) have shown to be successful. Sedative-anxiolytic treatment and relaxation training are also considered as options . Regardless of the approach, it is very important for physicians to be very patient and careful when dealing with individuals who experienced significant emotional trauma that resulted in memory loss, since an abrupt and often severe reaction may be seen with reintroduction of those memories.
The prognosis significantly varies from patient to patient. Memory loss may include a span of several days to years and the success of therapy primarily determines the outcome. Fortunately, many patient recover fully from memory loss and are able to cope with trauma they experience with the aid of therapists, but some, on the other hand, may never recover . It is important to emphasize that the risk of suicide is increased and underestimated in these patients , which is why it is important to obtain a diagnosis as soon as possible and initiate appropriate treatment.
Significant stress and psychological trauma are thought to be responsible for the onset of dissociative amnesia . In the vast majority of patients, a profoundly stressful event (death of a loved one, or physical abuse) precipitates the onset of memory loss. Current theories suggest overt activity of glucocorticoids in the amygdala and the hippocampus, resulting in suppression of neural activity . Amnesia is, by some authors, considered as a defense mechanism against the traumatic event and that repression or dissociation serves to protect against these harmful stimuli. Although genetic factors and individual baseline cortisol levels have been considered as important etiological factors as well  , their clear association remains the be determined.
Exact prevalence and incidence rates of dissociative amnesia are unknown, but crude rates suggest that between 2-6% of the population suffered from this condition . It is most frequently diagnosed in young adults, implying that younger age is a significant risk factors, as are history of previous emotional trauma (including its severity, repetitiveness and longer duration), injury to the hippocampus and the temporal lobe, but also elevated baseline levels of cortisol . Personality features, presence of either psychiatric or non-psychiatric comorbidities and the environment in which the individual resides have also shown to be important determinants .
In the setting of extensive emotional trauma, dissociative amnesia is considered as a mechanism of protection  and various biological events have been described. Additionally, a subtype of dissociative amnesia, known as dissociative fugue, is a term that describes intentional avoidance from harmful stimuli and further indicates that amnesia is most likely a protective response  . Namely, excess levels of glucocorticoids, the main stress hormones, have been identified in this subset of patients and their activity on the central nervous system and structures responsible for learning and memory have been well-documented. The amygdala and the hippocampus, the two most important structures that mediate arousal and memory, respectively, possess a very large number of glucocorticoid receptors . This abundant secretion of corticosteroids impairs normal activity of these structures and induces hippocampal atrophy, as well as defects in neural activity . Despite these discoveries, many elements in the pathogenesis remain to be confirmed.
Despite the fact that the presumable cause is more-or-less established, not all individuals respond equally to stress caused by unpredictable situations, which is why little can be done in terms of prevention. Child abuse has shown to be one of the most important events that trigger dissociative disorders and its prevention may lead to reduced rates of dissociative amnesia in the population.
The term dissociative (also known as psychogenic) amnesia denotes a retrograde blockade of memories that occurs in the setting of emotional trauma without evidence of organic disorders that may have triggered this event . In the vast majority of cases, inability to recall episodic-autobiographical memory is the main clinical symptom, but various studies have identified impairment of both semantic and procedural memories , which may have an effect on daily activities. Severe stressful and psychotraumatic events presumably influence the activity of the amygdala and hippocampus, as well as the frontal lobe and levels of corticosteroids . It is thought that abundant amounts of glucocorticoids are secreted in the setting of psychological stress, causing detrimental effects on the hippocampus, one of the main structures responsible for memory . Because dissociative amnesia is most frequently diagnosed in young adults , brain development has also been implicated as an important pathogenic factor . In order to make the diagnosis, it is imperative to obtain heteroanamnestic data (from both the patient and his/her family or friends) and identify traumatic events that may have triggered memory loss. In virtually all patients, only retrograde amnesia is evident, whereas anterograde amnesia is absent . Memory loss may include a time span of several hours of it may involve an extensive period of time, up to a few years . Other forms of dissociation may be included in the clinical presentation, such as personality disorder, which further emphasizes the importance of the patient interview. The diagnostic workup should exclude conditions that may have similar symptoms, such as physical trauma or drug abuse, which is why both imaging studies and a toxicology panel (if high clinical suspicion is present) should be conducted. Computed tomography (CT) and magnetic resonance imaging (MRI) are sufficient imaging studies to exclude trauma, while electroencephalography (EEG) should be done to rule out seizures . Functional activity of the brain can be evaluated through positron emission tomography (PET), with some studies showing decreased glucose utilization in the prefrontal cortex of patients who suffered from memory loss . Psychotherapy is the most important therapeutic measure and has shown marked success in retrieval of memories and dealing with psychological stress that was induced by these events . With successful therapy, many patients are able to fully recover, but a small number of individuals may never be able to restore their memory .
Dissociative amnesia is a condition in which severely stressful events (such as sexual abuse or death of a family member or friend) trigger a defensive mechanism that results in blockade of memories regarding that particular event. Although the exact reason why this happens is not completely clear, it is known that very high concentrations of stress hormones, such as cortisol, induce detrimental changes to the hippocampus, the part of the brain that is responsible for memory. Various contributing factors have been proposed, including genetic, environmental and prior physical trauma to the head. Because of the fact that dissociative amnesia is most commonly diagnosed in younger adults, age and appropriate brain maturation are termed to be one of the most important precipitating factors, together with baseline levels of cortisol. All of these components are through to be the reason why some individuals develop this condition, while some do not. Patients may present with variable mental state changes, ranging from normal to severely confused and it is not uncommon for other dissociative disorders, such as personality disorder, to be present. It may not be easy to obtain a diagnosis, which is why physicians should try to obtain information regarding previous trauma as patient and as careful as possible. Before making a definite diagnosis, drug abuse, physical trauma and epilepsy as potential causes should be excluded. Blood and urine toxicology tests, imaging studies such as computed tomography (CT scan) or magnetic resonance imaging (MRI) are done to rule out drug abuse and trauma, respectively, whereas electroencephalography (EEG) is done to rule out seizures. Ensuring a safe and pleasant environment for the patient is the first step in management, while further strategies include use of sedatives and anxiolytic drugs for hypnosis and psychotherapy, which has shown to be effective in both recovering memories and coping with emotional distress. The prognosis is generally good with appropriate treatment, as majority of individuals recover from dissociative amnesia, but a careful clinical approach is necessary in order to identify the exact type of amnesia and ensure proper therapy.