Amnestic disorders are isolated disturbances of memory without impairment of other cognitive functions. They may be due to a general medical condition or substance related.

Etiology
Amnestic disorders are caused by general medical conditions or substance use. Common general medical conditions include head trauma, hypoxia, herpes simplex encephalitis, and posterior cerebral artery infarction. Amnestic disorders often are associated with damage of the mammillary bodies, fornix, and hippocampus. Bilateral damage to these structures produces the most severe deficits. Amnestic disorders due to substance-related causes may be due to substance abuse, prescribed or over-the- counter medications, or accidental exposure to toxins. Alcohol abuse is a leading cause of substance- related amnestic disorder. Persistent alcohol use may lead to thiamine deficiency and induce Wernicke- Korsakoff’s syndrome.

If properly treated, the acute symptoms of ataxia, abnormal eye movements, and confusion may resolve, leaving a residual disorder called Korsakoff’s psychosis( alcohol-  induced persistent amnestic disorder).

Epidemiology
Individuals affected by a general medical condition or alcoholism are at risk for amnestic disorders.

Clinical Manifestations
History and Mental Status Examination
Amnestic disorders present as deficits in memory, either in the inability to recall previously learned information or the inability to retain new information. The cognitive defect must be limited to memory alone; if additional cognitive defects are present, a diagnosis of dementia or delirium should be considered. In addition to defect in memory, there must be an identifiable cause for the amnestic disorder (i.e., the presence of a general medical condition or substance use).

Differential Diagnosis
Delirium and dementia are the major differential diagnostic considerations. Amnestic disorders are distinguished from dissociative disorders on the basis of etiology. By definition, amnestic disorders are due to a general medical condition or substance.

Management
The general medical condition is treated whenever possible to prevent further neurologic damage; in the case of a substance-related amnestic disorder, avoiding reexposure to the substance responsible for the amnestic disorder is critical. Pharmacotherapy may be directed at treating associated anxiety or mood difficulties. Patients should be placed in a safe, structured environment with frequent memory cues.