Amnesia — a disturbance in, or loss of, memory — may be classified as partial or complete and as anterograde or retrograde.
• Anterograde amnesia denotes memory loss of events that occurred after the onset of the causative trauma or disease;
• retrograde amnesia, memory loss of events that occurred before the onset. Depending on the cause, amnesia may arise suddenly or slowly and may be temporary or permanent.
Organic (or true) amnesia results from temporal lobe dysfunction, and it characteristically spares patches of memory. A common symptom in patients with seizures or head trauma, organic amnesia can also be an early indicator of Alzheimer’s disease. Hysterical amnesia has a psychogenic origin and characteristically causes complete memory loss. Treatment-induced amnesia is usually transient
• Alzheimer’s disease.
Alzheimer’s disease usually begins with retrograde amnesia, which progresses slowly over many months or years to include anterograde amnesia, producing severe and permanent memory loss. Associated findings include agitation, inability to concentrate, disregard for personal hygiene, confusion, irritability, and emotional lability. Later signs include aphasia, dementia, incontinence, and muscle rigidity.
• Cerebral hypoxia.
After recovery from hypoxia (brought on by such conditions as carbon monoxide poisoning or acute respiratory failure), the patient may experience total amnesia for the event, along with sensory disturbances, such as numbness and tingling.
• Head trauma.
Depending on the trauma’s severity, amnesia may last for minutes, hours, or longer. Usually, the patient experiences brief retrograde and longer anterograde amnesia as well as persistent amnesia about the traumatic event. Severe head trauma can cause permanent amnesia or difficulty retaining recent memories. Related findings may include altered respirations and LOC; headache; dizziness; confusion; visual disturbances, such as blurred or double vision; and motor and sensory disturbances, such as hemiparesis and paresthesia, on the side of the body opposite the injury.
• Herpes simplex encephalitis.
Recovery from herpes simplex encephalitis commonly leaves the patient with severe and possibly permanent amnesia. Associated findings include signs and symptoms of meningeal irritation, such as headache, fever, and altered LOC, along with seizures and various motor and sensory disturbances (such as paresis, numbness, and tingling).
Hysterical amnesia, a complete and long-lasting memory loss, begins and ends abruptly and is typically accompanied by confusion.
In temporal lobe seizures, amnesia occurs suddenly and lasts for several seconds to minutes. The patient may recall an aura or nothing at all. An irritable focus on the left side of the brain primarily causes amnesia for verbal memories, whereas an irritable focus on the right side of the brain causes graphic and nonverbal amnesia. Associated signs and symptoms may include decreased LOC during the seizure, confusion, abnormal mouth movements, and visual, olfactory, and auditory hallucinations.
• Wernicke-Korsakoff syndrome.
Retrograde and anterograde amnesia can become permanent without treatment in this syndrome. Accompanying signs and symptoms include apathy, an inability to concentrate or to put events into sequence, and confabulation to fill memory gaps. The syndrome may also cause diplopia, decreased LOC, headache, ataxia, and symptoms of peripheral neuropathy, such as numbness and tingling.