The systematized type of dissociative amnesia is amnesia for certain categories of memory such as all memories relating to one’s family or to a specific person. Table 19.1 lists the different patterns of dissociative amnesia.

In dissociative identity disorder, although recovery is possible, it is generally incomplete. This is considered the most severe and chronic of the dissociative disorders. The earlier the onset of dissociative identity disorder, the poorer the prognosis is. The level of impairment ranges from moderate to severe and is determined by variables such as the number, the type, and the chronicity of the various personalities. The individual personalities may have their own separate mental disorders; mood disorders, personality disorders, and other distinctive disorders are most common. One or more of the personalities may function relatively well, and the others function marginally.

An occasional phenomenon of depersonalization disorder is doubling; patients believe that the point of consciousness is outside their bodies, often a few feet overhead, and from there, they observe themselves as if they were totally separate persons. Sometimes patients believe that they are in two places at the same time, a condition called reduplicative paramnesia or double orientation. Most patients are aware of their disturbed sense of reality; this awareness is considered one of the salient characteristics of the disorder. Dissociation is defined as an unconscious defense mechanism involving the segregation of any group of mental or behavioral processes from the rest of the person’s psychic activity; this may entail the separation of an idea from its accompanying emotional tone, as seen in dissociative and conversion disorders. Déjà vu is an illusions of visual recognition in which a new situation is incorrectly regarded as a repetition of a previous experience.

There are a number of culture-bound psychiatric syndromes in which fugue is a prominent feature. These syndromes include the “running” syndromes, which include latah and amok, that occur in several nations along the western Pacific rim; grisi siknis, occurring among the Miskito of Nicaragua and Honduras; and piblokto (Arctic hysteria), occurring among the Eskimos of northern Greenland. These syndromes are characterized by a high level of agitation, running about, trance-like states, and amnesia for the episode.

The classic (not nonclassic) presentation of dissociative amnesia is an overt, florid, dramatic clinical disturbance that frequently results in the patient’s being brought quickly to medical attention specifically for symptoms related to the dissociative disorder. In the nonclassic dissociative amnesia, on the other hand, patients frequently come to treatment for a variety of symptoms other than the dissociative symptoms and the amnesia (e.g., depression, mood swings, anxiety). The nonclassic presentation of dissociative amnesia can be said to have a covert dissociative syndrome because their primary complaints infrequently relate directly to amnesia. Chronic, recurrent, or persistent dissociative amnesia, or a combination of these, is the most common symptom in these cases, although some may also describe a history of fugue-like states. Commonly, patients with the nonclassic presentations of amnesia do not reveal the presence of dissociative symptoms unless directly asked about them. These patients are often uncomfortable when amnesia is inquired about and may minimize the presences or rationalize the importance of the symptoms.

In patients with nonclassic dissociative amnesia, the amnesia manifests itself as a circumscribed memory gap or series of memory gaps for the life history, primarily for times when traumatic events occurred, such as childhood or wartime. Self-mutilation and violent behavior in these patients may also be accompanied by amnesia. Amnesia may also occur for flashbacks or behavioral reexperiencing episodes related to trauma.

Amnestic disorders are caused by a variety of organic conditions. Examples of organic causes of amnesia are epileptic seizure, head trauma, alcoholic blackouts, Korsakoff’s syndrome, stroke, postoperative amnesia, postinfectious amnesia, after electroconvulsive therapy (ECT), surgery, infection, and transient global amnesia. Less common causes are cerebrovascular disease, metabolic abnormalities, and toxic states.

Organic amnesias have several distinguishing features: they do not normally involve recurrent identity alteration, the amnesia is not selectively limited to personal information, the memories do not focus on or result from an emotionally traumatic event, and the amnesia is more often anterograde than retrograde. In cases of amnesia of organic etiology (excluding substance abuse, transient global amnesia, and metabolic abnormalities), the amnesia is usually permanent and does not lend itself to therapeutic technique. Whereas dissociative amnesia represents a displacement of the memory from awareness, organic amnesias represent the erasure or destruction of that memory through disturbance of the neuropsychological process.

Transient global amnesia is an acute and transient retrograde amnesia that affects recent, more than remote, memories. Although patients are usually aware of the amnesia, they may still perform highly complex mental and physical acts during the 6 to 24 hours that transient global amnesia episodes usually last. Recovery from the disorder is usually complete. Transient global amnesia is most often caused by transient ischemic attacks that affect limbic midline brain structures. It can also be associated with migraine headaches, seizures, and intoxication with sedative-hypnotic drugs.