Amnesia overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:  Zehra Malik, M.B.B.S[2]

## Overview

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Amnesia can be divided into two broad groups, retrograde amnesia and anterograde amnesia. Retrograde amnesia is the loss of memory prior to the onset of amnesia and anterograde amnesia is the inability to form new memory. Memory can also be divided into two groups depending on the duration, short-term memory and long-term memory. Other types of amnesia are Psychological including repressive amnesia and dissociative fugue, infantile amnesia, neurological amnesia (Alzheimer's disease, Pick's disease), post-traumatic Amnesia, drug-Induced Amnesia, transient global amnesia, amnesia due to nutritional deficiency (thiamine, vitamin B12). Richard Semon in 1904 described that experiences cause some changes in the neurons and these changes are referred to as engram and they form memory of the particular experience in those neurons. Reactivation of these neurons occur when patient tries to recall those memories. Amnesia results from damage to different memory centers in the brain, such as the medial temporal lobe and the hippocampus, which are involved in acquiring and restoring memory. Common causes of amnesia include medications, head trauma, depression and aging. Less common cause of amnesia are childhood sexual abuse, traumatic incident, hypoxia, psychological trauma, thiamine deficiency, alcohol abuse, Alzheimer's disease, Pick's disease, Parkinson's disease, benzodiazepines, hypoglycemia, stroke, electroconvulsive therapy. The underlying etiology of memory loss must be differentiated on the basis of duration of memory loss, presence of anterograde amnesia or retrograde amnesia, associated features, and cognitive impairment. Memory impairment tends to increase with age. Forty percent of the population over age sixty have some degree of memory loss. Amnesia and mild cognitive impairment is more prevalent in middle-aged to older Non-Hispanic Black and older Latino as compared to non-Hispanic Whites. Aging, depression, chronic stress, head trauma, chronic sleep deprivation and medications are risk factors ​for amnesia. Amnesia may progress slowly or suddenly, and maybe transient or permanent. The natural history and prognosis depends upon the underlying etiology. Patients with memory loss could suffer from depression and grief long term. Quality of life and activities of daily living are difficult to maintain which causes decreased socialization and a decline in cognitive functions in the elderly.Amnesia is largely a clinical diagnosis, a detailed history of memory impairment and associated symptoms should be obtained. Focal examination including vital signs, altered mental status, mini mental status exam (MMSE), Glasgow Coma Scale, nystagmus, papilledema, gait, instruments of daily activities should be assessed. Head CT scan and MRI may be helpful in identifying structural and functional abnormalities including bleeding, stroke, tumor, atrophy or any changes suggestive of amnesia. Positron emission tomography PET may show hypometabolism in areas of brain associated with memory in patients with history of amnesia but with no visible structural or functional brain damage on CT scan or MRI. Other diagnostic studies helpful in the diagnosis of the cause amnesia are EEG for epilepsy, CSF fluid analysis for encephalitis.Treatment can be offered in cases of reversible conditions. If not, provision of supportive care can help to improve a patient's condition. Etiology specific treatment plan should be followed to improve memory and delay progression. Surgical intervention is not recommended for the management of memory loss. Measures for the primary prevention of amnesia include preventing brain trauma, managing stress, avoid alcohol abuse, manage stroke risk factors, good sleep habits, social integration, optimum nutrition and exercise routine. Effective measures for the secondary prevention of memory loss include, sustainable daily routine, healthy eating habits, social integration, exercise routine, reduce and manage stress, adequate sleep, reading and playing strategic games like puzzles and word games.

## Historical Perspective

[edit | edit source]

Richard Semon in 1904 described that experiences cause some changes in the neurons and these changes are referred to as engram and they form memory of the particular experience in those neurons. Reactivation of these neurons occur when patient tries to recall those memories. Theodule-Armand Ribot, a French psychologist determined that memory loss affects recent memories first. Memories are lost in reverse order of their development.

## Classification

[edit | edit source]

Amnesia can be divided into two broad groups, retrograde amnesia and anterograde amnesia. Retrograde amnesia is the loss of memory prior to the onset of amnesia and anterograde amnesia is the inability to form new memory. Other types of amnesia are Psychological including repressive amnesia and dissociative fugue, infantile amnesia, neurological amnesia (Alzheimer's disease, Pick's disease), post-traumatic Amnesia, drug-Induced Amnesia, transient global amnesia. Memory can also be divided into two groups depending on the duration, short-term memory and long-term memory.

## Pathophysiology

[edit | edit source]

Amnesia results from damage to different memory centers in the brain, such as the medial temporal lobe and the hippocampus, which are involved in acquiring and restoring memory.

## Causes

[edit | edit source]

Common causes of amnesia include medications, head trauma, depression and aging. Less common cause of amnesia are childhood sexual abuse, traumatic incident, hypoxia, psychological trauma, thiamine deficiency, alcohol abuse, Alzheimer's disease, Pick's disease, Parkinson's disease, benzodiazepines, hypoglycemia, stroke, electroconvulsive therapy.

## Differentiating Amnesia from other Diseases

[edit | edit source]

The underlying etiology of memory loss must be differentiated on the basis of duration of memory loss, presence of anterograde amnesia or retrograde amnesia, associated features, and cognitive impairment.

## Epidemiology and Demographics

[edit | edit source]

Memory impairment tends to increase with age. Forty percent of the population over age sixty have some degree of memory loss. Amnesia and mild cognitive impairment is more prevalent in middle-aged to older Non-Hispanic Black and older Latino as compared to non-Hispanic Whites.

## Risk Factors

[edit | edit source]

Aging, depression, chronic stress, head trauma, chronic sleep deprivation and medications are risk factors ​for amnesia.

## Natural History, Complications and Prognosis

[edit | edit source]

Amnesia may progress slowly or suddenly, and maybe transient or permanent. The natural history and prognosis depends upon the underlying etiology. Patients with memory loss could suffer from depression and grief long term. Quality of life and activities of daily living are difficult to maintain which causes decreased socialization and a decline in cognitive functions in the elderly.

## Diagnosis

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### Diagnostic Study of Choice

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There is no diagnostic study of choice to diagnose amnesia. The best approach is to obtain a detailed history followed by a focused physical examination.

### History and Symptoms

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It is critical to perform a formal and exhaustive assessment of the patient to look for any indications of memory disorders and to hear any subjective complaints. With this information, preventative measures and care can be specifically addressed to the patient's needs. A detailed history of memory loss and associated symptoms is crucial for understanding the etiology of amnesia.

### Physical Examination

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Patients with amnesia may have variable general appearance depending on the underlying cause of memory loss. Amnesia is largely a clinical diagnosis. Focal examination including vital signs, altered mental status, mini mental status exam (MMSE), Glasgow Coma Scale, nystagmus, papilledema, gait, instruments of daily activities should be assessed.

### Laboratory Findings

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There is no laboratory test to diagnose memory loss. however, it is important to obtain toxicology screening, alcohol, glucose, electrolytes level.

### Electrocardiogram

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There are no ECG findings associated with amnesia.

### X-ray

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There are no x-ray findings associated with amnesia.

### Echocardiography and Ultrasound

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There are no echocardiography/ultrasound findings associated with amnesia. Although a case of transient global amnesia has been reported in a patient undergoing a transesophageal echocardiogram (TEE).

### CT

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Head CT scan may be helpful in the diagnosis of the cause of amnesia. Structural and functional abnormalities are identified to detect any bleeding, stroke, tumor, atrophy or any changes suggestive of amnesia.

### MRI

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Head MRI may be helpful in the diagnosis of the cause of amnesia in some cases including, Alzheimer's disease, or brain trauma. In majority of the cases of amnesia the brain appears normal on MRI.

### Other Imaging Findings

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Positron emission tomography PET may show hypometabolism in areas of brain associated with memory in patients with history of amnesia but with no visible structural or functional brain damage on CT scan or MRI.

### Other Diagnostic study

[edit | edit source]

Other diagnostic studies helpful in the diagnosis of the cause amnesia are EEG for epilepsy, CSF fluid analysis for encephalitis.

## Treatment

[edit | edit source]

### Medical Therapy

[edit | edit source]

Treatment can be offered in cases of reversible conditions. If not, provision of supportive care can help to improve a patient's condition. Etiology specific treatment plan should be followed to improve memory and delay progression. When memory loss is a symptom of a more severe disease, it may be reversed as soon as the underlying condition is identified and cured. Memory loss due to aging cannot be cured, but the symptoms may be improved by preventative measures.

### Surgery

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Surgical intervention is not recommended for the management of memory loss.

### Primary Prevention

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Measures for the primary prevention of amnesia include preventing brain trauma, managing stress, avoid alcohol abuse, manage stroke risk factors, good sleep habits, social integration, optimum nutrition and exercise routine.

### Secondary Prevention

[edit | edit source]

Effective measures for the secondary prevention of memory loss include, sustainable daily routine, healthy eating habits, social integration, exercise routine, reduce and manage stress, adequate sleep, reading and playing strategic games like puzzles and word games.

## References

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