Dissociative amnesia

Memory loss, a problem commonly seen in medical practice, may be retrograde, anterograde, partial or total. Causes of memory loss may be structural, pharmacologic or psychiatric. [1-9] Of the psychiatric causes, psychogenic amnesia is the most common and perhaps the best described, with nearly 1,000 cases documented since the 1870s. [1-7] During periods of public emergency, this form of amnesia may be responsible for 15 percent of all psychiatric admissions. [5] Since family physicians may encounter psychogenic amnesia in a number of clinical settings, including physical assault, natural disasters and family crises, they need to be familiar with its clinical features, treatment and prognosis.

Definition and History

Psychogenic amnesia is a psychiatric disorder characterized by a sudden loss of memory covering a variable period of time, an absence of underlying brain disease and an awareness by the patient that a memory disturbance is present. [1] Except in its generalized form, this disorder is nearly always characterized by anterograde amnesia (i.e., loss of memory for a period following a profoundly distressing event). [1,9]

Psychogenic amnesia was first classified with conversion disorder as a hysterical neurosis in the late 1800s. [1,7] In the first edition of the Diagnostic and Statistical Manual of Mental Disorders (1952), [8] psychogenic amnesia was recognized as an independent process, separated from conversion disorder and reclassified with dissociative disorders involving alteration of consciousness or identity. Dissociative disorders, including psychogenic amnesia, remain in a separate classification from conversion disorder in the revised third edition of the American Psychiatric Association's manual (1987). [9] In psychogenic amnesia, a suspected internal conflict is manifested by memory loss and subsequent dissociative state, while in conversion disorder, internal conflict is manifested by sensorimotor symptoms. [9]

Illustrative Case

A 33-year-old airborne trainee who had been in good health was evaluated at a U.S. Army hospital after he was found lying face down in the hospital parking lot. He could not recall how he had lost consciousness or how long he had been in the parking lot.

On physical examination, the patient was confused but cooperative, respectful and upset about his memory loss. No evidence of physical trauma was present. He was disoriented to person, place and time and had total amnesia regarding the events before he was found in the parking lot. Mental status examination revealed a generalized absence of remote and intermediate memory but good short-term memory for all events following his presentation to the hospital. Except for the disorientation and memory loss, his neurologic examination was normal.

In a follow-up examination at a mental health center, the patient's available social history revealed an excellent military record with no prior evidence of psychiatric illness. The Minnesota Multiphasic Personality Inventory test demonstrated no abnormal personality features. Because the patient's history of head trauma was unclear, computed tomographic (CT) scanning was performed; those results were also normal.

Since there was no evidence of trauma or other underlying abnormality in the patient, the attending physicians suspected a psychiatric illness, and the patient was subsequently interviewed twice under hypnosis. During these interviews, he could remember many childhood experiences, but no precipitating event for the amnesia could be identified.

In follow-up interviews under hypnosis, the patient could not recall ever having been married. However, when his wife was contacted and involved in his therapy, he adjusted well to the revelation of his marriage. The patient's wife related that he had been a musician and had enlisted in the Army in order to play in the military band. His subsequent failure to qualify for the band had depressed him. He also (mistakenly) understood his wife to have a serious kidney disorder that would eventually require transplantation, and he wished to be with her. Finally, the news that he was to be transferred to Korea for an unaccompanied tour after airborne training had caused him great distress.

On the basis of the history and the interview findings, it was hypothesized that the patient's amnesia was precipitated by the anticipated prolonged separation from his wife and his concern that she might be dying from the kidney ailment. Urologic consultation was obtained to dispel the patient's misunderstanding about his wife's illness. Plans for airborne training and assignment to Korea were deferred, and the patient's memory, which had been returning only in small fragments during therapy sessions, began coming back quickly. At the time of transfer to his next duty station, the patient had regained essentially all of his lost memory.

Clinical Characteristics

PRECIPITANTS

As typified by the patient in the illustrative case, psychogenic amnesia often occurs in adolescents and young adults who have no history of psychiatric illness. Furthermore, it generally occurs in close association with a stressful event that involves (or is perceived to involve) serious threat to life or health. The amnesia may follow physical trauma and often involves conflicts over sexual or aggressive drives. Documented precipitants have included natural disasters (e.g., earthquakes, floods), marital discord, physical assault, personal threats, and war or military-related activities. [1-7,10-12]

CLASSIFICATION

Psychogenic amnesia may assume several forms. [9] The most common of these is localized memory loss, covering a few hours after the stressful event. In generalized amnesia, years or even a lifetime of memories may be lost (as in the illustrative case); amnesia in this uncommon form may be nearly total. [6] In the rare systematized form, memory loss occurs for a specific event, while other events simultaneously experienced are recalled. Another rare form of psychogenic amnesia is continuous amnesia; in this form of the disorder, memory loss occurs for each successive event as it occurs, but alertness and awareness are not disturbed.

MECHANISMS

Several etiologic mechanisms have been proposed to account for the presentations of psychogenic amnesia. A neurobiologic hypothesis holds that the disorder results from cortical inhibition of afferent stimulation. [10] This hypothesis is supported by studies showing that benzodiazepines and barbiturates are effective in treating psychogenic amnesia. [1, 7,13,14] These drugs produce disinhibition of corticofugal pathways in the brain.

A behavioral theory suggests that psychogenic amnesia may, paradoxically, represent a "recently learned" phenomenon that may be treated by the elimination of recent memory. In some studies, [11-15] chemical and electroconvulsive shock therapies that selectively impair recent memory have been used with some success in the treatment of psychogenic amnesia.

The most popular hypothesis is psychoanalytic and suggests that the disorder represents an unconscious attempt to avoid an intolerable conflict. Indeed, psychogenic amnesia often improves spontaneously with apparent resolution of the underlying conflict, even in the absence of pharmacologic or electroconvulsive shock therapy.

Differential Diagnosis

PSYCHIATRIC DISORDERS

Psychiatric disorders that may cause amnesia include somnambulism, schizophrenia, fugue states and malingering, as well as psychogenic amnesia. Patients with somnambulism often appear to be in a dream state during amnestic spells, while patients with psychogenic amnesia appear fully alert. Schizophrenic patients typically present with auditory hallucinations and/or abnormalities of thought content. Patients with psychogenic fugue states can be distinguished from those with psychogenic amnesia by their involvement in purposeful travel or the acquisition of a new identity. [16]

Malingerers frequently present with amnesia. Reports [17,18] indicate, for example, that 23 to 65 percent of murderers claim amnesia for their crimes. Malingering may be identified by the history, by observation and through hypnotic interviews. [1,7,19] Lack of anxiety and concern about the memory loss suggests malingering, as does resistance to memory recall during interviews using amobarbital (Amytal) and/or hypnosis.

SUBSTANCE ABUSE

Substance abuse syndromes that mimic psychogenic amnesia include alcoholism with subsequent "blackout spells," cocaine or other stimulant abuse with subsequent psychosis, or the use of hallucinogenic agents such as lysergic acid diethylamide (LSD) or phencyclidine (PCP). [1,2,20] A number of commonly used drugs, such as tricyclic antidepressants, digoxin (Lanoxin) and aminophylline in toxic doses, have also been implicated in amnesia (Table 1). [2,8,9,19]

With the exception of alcohol, which in chronic alcoholism may induce permanent alteration of memory, amnesia associated with drug use or abuse is transient and benign, resolving rapidly with discontinuance of the offending agent. Substance use may be excluded as a cause of amnesia by a thorough history and judicious drug screening.

STRUCTURAL BRAIN DISORDERS

Numerous structural brain disorders, including vascular disorders, encephalitis, encephalopathy, dementing disorders and trauma, may cause amnesia (Table 2). [1,2,7,11,18,19] Generally, these disorders can be identified by the history and an abnormal neurologic examination. The diagnosis may be verified by CT scanning of the head, electroencephalography, lumbar puncture and laboratory findings, including erythrocyte sedimentation rate, cultures and, occasionally, brain biopsy.

Temporal lobe seizures, either congenital or resulting from trauma, infection or ischemia, commonly produce amnesia and often involve preictal aurae. These seizures can usually be ruled out by a normal sleep-deprived electroencephalogram (EEG).

Amnesia may also be the result of concussion. [1,2,20] Unlike psychogenic amnesia, postconcussive amnesia is generally retrograde (i.e., loss of memory for events preceding the trauma). Regardless of therapy, patients with postconcussive amnesia experience slow, gradual recall of memory. In contrast, aggressive treatment leads to rapid, consistent recall of memory in almost all patients with psychogenic amnesia. Evaluation

In evaluating the patient with new-onset amnesia, the physician should obtain a pertinent history of the events surrounding the period of memory loss and any associated changes in the patient's personality, thought processes and affect. A thorough neurologic examination, with close attention to mental status abnormalities, should be performed. A relevant social history should be obtained from family, colleagues and friends, if possible. Consideration should be given to prescription or illicit drug use, and appropriate drug screening may be warranted.

Diagnostic studies, including a CT scan and, in some cases, EEGs (with and without sleep deprivation), can assist in ruling out structural brain disorders. If no organic cause for the amnesia can be found, the patient should be referred for hypnotic or amobarbital interviews to distinguish among the psychiatric causes of memory loss. If psychogenic amnesia is considered the underlying disorder, treatment with psychotherapy, hypnosis and, possibly, electroconvulsive shock therapy can be initiated.

Treatment and Prognosis

The diversity of treatments for psychogenic amnesia reflects the uncertainty about its etiology. In general, the prognosis for improvement is considered good, and aggressive treatment leads to rapid recovery of memory. Treatment may involve observation with expectation of spontaneous recovery, behavioral modification, supportive psychotherapy or pharmacotherapy. [1,7,8,10,11, 19,21,22] Of these methods, psychotherapy is the most common form of treatment and may involve use of the free-association technique to facilitate memory recall. Using this technique, the patient attaches associations to memory fragments in the form of a conscious image or dream. [1,23]

When used with amobarbital or the hypnotic interview, suggestion may also be effective in treating psychogenic amnesia. [1,7,14,22] In several studies, [11,15] total resolution of amnesia occurred after three to five sessions of chemical or electroconvulsive shock therapy. Electroconvulsive shock therapy may be particularly effective when the amnesia is associated with clinical depression.

Since psychogenic amnesia may occur as a protective mechanism in suicidal persons, suicidal ideation may surface when the amnesia is treated. [12] Precautions should be undertaken to prevent suicidal actions during ongoing therapy.

All forms of potential secondary gain should be investigated and eliminated. Underlying causes and mechanisms must be removed, or relapses will remain a constant possibility. If major depression is not coexistent, the patient can be made aware of potential underlying conflicts and precipitants for the amnesia, and appropriate coping mechanisms can be instituted, thereby minimizing relapses. Assuming these conditions are met, employment potential is not significantly affected. [1,21,22]

Final Comment

Although many disorders that cause memory loss require protracted treatment and carry a poor prognosis, psychogenic amnesia frequently resolves quickly and completely with treatment. It is therefore important for the physician to consider this diagnosis in any patient presenting with memory loss of no clear etiology. The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the U. S. Army or the Uniformed Services University of the Health Sciences.

COPYRIGHT 1990 American Academy of Family Physicians
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