Description

• A single disease process can manifest with abnormalities in more than one memory system.
• For example, Alzheimer disease sufferers have a notable deficit in semantic memory, but can also have working memory deficits.
• Amnestic disorder, amnestic syndrome, or simply amnesia comes from the Greek for forgetfulness.
• Indicates a loss of, or gap in, one’s memory, usually due to brain injury, shock, fatigue, repression, or illness
• Can be categorized based on amnesia for:
  • Events prior to the causative event, as in retrograde
  • Events after the causative event, as in anterograde
  • Information related to all senses and past experiences, as in global amnesia

Epidemiology

Incidence and prevalence of amnesia is in direct proportion to the epidemiology of the primary cause.

Incidence
Transient global amnesia (TGA) is one type of amnestic disorder found in one study to occur at of rate of 6.8 cases per 100,000 people per year (1).

Risk Factors

Genetics
Recent evidence supports the possibility of a genetic predisposition to developing TGA (2).

Pathophysiology

• Amnestic disorder is a syndrome that can be caused by many distinct disease processes, including head trauma, global hypoxia, cardiovascular accident (CVA), alcohol consumption/abuse, seizure, dissociative amnesia, TGA, encephalitis, tumor, and paraneoplastic limbic encephalitis.
• In most causes of amnesia, some damage or disruption (either temporary or permanent) occurred to the limbic structures in the brain responsible for memory.
• TGA is well studied, but is not fully understood, and may be related to venous congestion of the brain.

Etiology

• In general, metabolic or structural changes that cause an imbalance in the memory-related regions of the brain can cause an amnestic disorder.
• Common causes:
  • Thiamine deficiency
  • Hypothalamic tumors
  • Vertebrobasilar ischemia
• Less common:
  • Neurodegenerative dementias such as Alzheimer disease
  • Bilateral damage to the medial temporal lobes
  • Head trauma
  • Chronic alcoholism
  • Nutritional disorders
  • In the case of dissociative amnesia, extreme psychological trauma causes the deficit.
• The exact cause of TGA is not well understood, but it has been associated with:
  • Physical exertion
  • Emotional stress
  • Pain
  • Exposure to cold water
  • Sexual intercourse
  • Valsalva maneuver
  • Malingering and factitious disorder should also be considered.

Commonly Associated Conditions

• Some relationship has been found between migraines and TGA.
• Patients with TGA were found to have a higher frequency of psychiatric disease relative to transient ischemic attack controls in one study.