“As an undergraduate student in psychology, I was taught that multiple personalities were a very rare and bizarre disorder. That is all that I was taught on ... It soon became apparent that what I had been taught was simply not true. Not only was I meeting people with multiplicity; these individuals entering my life were normal human beings with much to offer. They were simply people who had endured more than their share of pain in this life and were struggling to make sense of it.”
― Deborah Bray Haddock, The Dissociative Identity Disorder Sourcebook
The DSM-5 gives the following criteria for a diagnosis of dissociative amnesia:
A. An inability to recall important autobiographical information, usually of a traumatic or stressful nature, that is inconsistent with ordinary forgetting.
Note: Dissociative amnesia most often consists of localized or selective amnesia for a specific event or events; or generalized amnesia for identity and life history.
B. The symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.
C. The disturbance is not attributable to the physiological effects of a substance (e.g., alcohol or other drug of abuse, a medication) or a neurological or other medical condition (e.g., partial complex seizures, transient global amnesia, sequelae of a closed head injury/traumatic brain injury, other neurological condition).
D. The disturbance is not better explained by dissociative identity disorder, posttraumatic stress disorder, acute stress disorder, somatic symptom disorder, or major or mild neurocognitive disorder.
...With dissociative fugue: Apparently purposeful travel or bewildered wandering that is associated with amnesia for identity or for other important autobiographical information (American Psychiatric Association, 2013)1.
Criterion A refers to a lack of retrievable memory regarding personal information or history that should be remembered and would normally be remembered. This does not cover items such as forgetting where one placed one's keys, what one did the day before, or who one's sixth grade teacher was. Instead, it covers: selective amnesia (an absence of some but not all memories regarding a specific incident or period of time, such as knowing where and how an assault occurred but being unable to picture or remember anything about the old friend who was behind it or being unable to access any memories regarding one's abusive family); localized amnesia (a complete absence of memory regarding a specific incident or period of time, such as a period of time during which one was abused as a child or witnessed intense combat); generalized amnesia (a complete absence of memory regarding one's history or personal identity; factual (semantic) and skill-based (procedural) knowledge may or may not be affected). While generalized amnesia is acute onset and obvious in the confusion and disorientation that it causes, selective and localized amnesia are often greatly minimized or even unacknowledged by those suffering from them, and they can be continuous, causing individuals to forget new traumatic events as they occur.
Criterion B excludes normal forgetting by ensuring that non-dysfunctional forgetting is not classified as amnesia. It is normal to be unable to remember some events, locations, people, or details even when such things are related to trauma or are associated with something highly stressful. That is not what dissociative amnesia seeks to describe. Many individuals with dissociative amnesia struggle to form lasting relationships, are re-victimized due to learned or internalized patterns of behavior, experience dissociative flashbacks, or engage in self harm or attempt suicide. Other neurological and behavioral effects of trauma are common.
Criterion C specifies that the amnesia not be due to a substance or neurological condition. Substance related "black outs" do not warrant a diagnosis of dissociative amnesia, nor does memory loss caused by and immediately preceding traumatic brain injury. Some individuals with seizure disorders may be unable to recall their behavior during a seizure or may experience a loss of old memories due to a seizure, but this memory loss is more random than that of dissociative amnesia and can be associated with abnormal brain activity. Finally, normally memory loss due to aging is not equivalent to dissociative amnesia.
Criterion D specifies that the amnesia not be due to another disorder. Amnesia for individuals with dissociative identity disorder is less stable than for those with dissociative amnesia, it often covers everyday events, and it can involve fluctuations associated with switching between alters. Individuals with posttraumatic stress disorder (PTSD) may have dissociative amnesia, but this diagnosis is not given if their memory loss pertains only and directly to the traumatic incident. The memory loss associated with neurocognitive disorders, unlike dissociative amnesia, impairs intellectual and cognitive functioning.
Dissociative amnesia may or may not involve traveling from one location to another that is associated with the amnesia.
Dissociative amnesia is not permanent nor caused by neurobiological damage or toxicity. It is often caused by single or repeated traumatic experiences, with a high number of traumatic experiences (such as repeated abuse) making dissociative amnesia more likely. Other risk factors include interpersonal violence and more severe trauma. In highly socially restricted cultures, dissociative amnesia can be associated with marital conflict, family disturbances, or oppression (American Psychiatric Association, 2013)1.
It's been found that 1.8% of the US population has dissociative amnesia. Dissociative amnesia is thought to affect 1.0% of males and 2.6% of females. It can be present in individuals of all ages (American Psychiatric Association, 2013)1.
Onset of dissociative amnesia may be sudden or delayed. The amnesia may last for only a short period of time or for years. It may resolve spontaneously when the afflicted individual is removed from the stressful or traumatic situation, or it may resolve slowly over the course of years. The gradual loss of dissociative amnesia and the return of traumatic memories can be highly stressful and can cause symptoms of PTSD or suicidal urges. Dissociative flashbacks may alternate with amnesia regarding the recovered content (American Psychiatric Association, 2013)1.
1 American Psychiatric Association. (2013). Dissociative Disorders. In Diagnostic and statistical manual of mental disorders (5th ed.). http://dx.doi.org/10.1176/appi.books.9780890425596.dsm08