Amnesia overview

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

Overview

Amnesia (from Greek Ἀμνησία) is a condition in which memory is disturbed or lost. The causes of amnesia can be organic or functional. Organic causes include damage to the brain through trauma or disease, or use of certain (generally sedative) drugs. Functional causes are psychological factors, such as defense mechanisms. Hysterical post-traumatic amnesia is an example of this. Amnesia may also be spontaneous, in the case of transient global amnesia. This global type of amnesia is more common in middle-aged to elderly people, particularly males, and usually lasts less than 24 hours. Memory loss can be partial or total, and is normally expected as we get older.

Classification

Amnesia can classified based upon various neuropsychopathologies. It is important to consider the etiological, organic, progressive and clinical criteria in amnesia classification. Amnesia can be classified based on the temporal nature of the amnesia, which is anterograde if the person forgets what occurs after the inciting event, or retrograde if the person forgets everything that occurred before the inciting event. Amnesia can also be classified based upon the nature, type, and pathophysiology of the amnestic episode.

Pathophysiology

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

Common causes of amnesia include medications, head trauma, depression and aging.

Risk Factors

Aging, depression and medications (both prescription and non-prescription) are risk factors for amnesia.

Diagnosis

History and Symptoms

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.

Physical Examination

The physical examination includes a detailed test of thinking and memory (mental status examination or neurocognitive test), and an examination of the nervous system. Recent, intermediate, and long-term memory should be tested.

MRI

Psychogenic amnesia is defined by the lack of structural damage to the brain, but upon functional imaging, abnormal brain activity can be seen. Tests using functional magnetic resonance imaging suggest that patients with psychogenic amnesia are unable to retrieve emotional memories normally during the amnesic period, suggesting that changes in the limbic functions are related to the symptoms of psychogenic amnesia.[1]

Other Imaging Findings

By performing a positron emission tomography activation study on psychogenic amnesic patients with face recognition, it was found that activation of the right anterior medial temporal region including the amygdala was increased in the patient whereas bilateral hippocampal regions increased only in the control subjects, demonstrating again that limbic and limbic-cortical functions are related to the symptoms of psychogenic amnesia.[2] Transient global amnesia is distinct in that abnormalities in the hippocampus can sometimes be visualized using a special form of magnetic resonance imaging of the brain known as diffusion-weighted imaging (DWI).

Treatment

Medical Therapy

Treatment can be offered in cases of reversible conditions. If not, provision of supportive care can help to improve a patient's condition.

References

  1. Yang JC, Jeong GW, Lee MS; et al. (2005). "Functional MR imaging of psychogenic amnesia: a case report". Korean J Radiol. 6 (3): 196–9. PMID 16145296.
  2. Yasuno F, Nishikawa T, Nakagawa Y; et al. (2000). "Functional anatomical study of psychogenic amnesia". Psychiatry Res. 99 (1): 43–57. PMID 10891648.




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