Amnestic State
An amnestic state is a persisting difficulty registering new memories, combining both an inability to learn new information and an inability to recall recently learned material, while memories from the more distant past, and immediate recall, both remain intact. As recovery occurs the affected period may shrink, and in some cases resolve fully.
This has traditionally required the absence of other prominent signs of cognitive impairment (as would be seen in dementia) or clouded consciousness (as in delirium) before the diagnosis is made, isolating it specifically to a disturbance of memory rather than a more global disturbance of mental function.
Recognition features
- A persisting difficulty forming new memories (anterograde) together with difficulty recalling recently learned material (retrograde)
- Memory for the distant past, and immediate, moment-to-moment recall, both remain relatively intact
- General cognitive function outside of memory, and level of consciousness, are both preserved, distinguishing this from dementia and delirium respectively
- May improve or shrink in extent with recovery, and in some cases resolve substantially or completely
Eliciting it at interview
- Test both the ability to learn new material (for example, a short list of words recalled after a delay) and the ability to recall recent versus remote personal history
- Assess general cognition and level of consciousness separately, since both need to be relatively preserved for this specific diagnosis to apply
- Reassess over time to track whether the amnestic period is shrinking, which is a useful indicator of ongoing recovery
Distinguishing features
- Differs from dementia in that other cognitive functions besides memory remain relatively preserved
- Differs from delirium in that consciousness remains clear rather than clouded
- Korsakoff's syndrome, caused by thiamine deficiency, is the classic example of this presentation, though it can also result from cerebrovascular disease, multiple sclerosis, transient global amnesia, head injury, and electroconvulsive treatment
Common misconceptions
- That an amnestic state is the same as dementia; the diagnosis specifically requires that other cognitive domains remain relatively spared
- That an amnestic state always has an alcohol-related cause; while Korsakoff's syndrome is the best-known example, several other organic causes are recognised
Related phenomena
Organic Amnesia · Retrograde Amnesia · Anterograde Amnesia · Ribot's Law of Memory Regression
Related syndromes
Practice this
A patient following prolonged heavy alcohol use and poor nutrition cannot recall anything told to her five minutes ago and cannot recall events from the past several weeks, yet she can hold a fluent conversation, recall her childhood clearly, and immediately repeat a phone number just given to her. What is this? · A patient recovering from a serious head injury three months ago can recall his life in vivid detail up to the day before the injury, and now shows normal immediate recall on testing (repeating a list of words just given to him), but cannot remember anything from the days spent in intensive care or reliably learn new information day-to-day. Before revealing the answer: is this an amnestic state? · One patient develops broad difficulty with memory, concentration, and everyday tasks alongside a severe, unmistakable low mood, is acutely distressed by her own decline, and recovers her cognitive function almost completely once the depression is treated. A second patient, following a head injury with no mood disturbance at all, cannot learn or recall any new information from the day of the injury onward, while his other cognitive abilities, immediate recall, and memories from before the injury all remain intact. Are both of these best understood as depressive pseudodementia? · A patient shows a marked pattern of memory loss. Before revealing the answer, decide what distinguishes Ribot's law of memory regression from an amnestic state. · You suspect a patient may have an amnestic state rather than dementia. Which single bedside approach would most efficiently help distinguish the two? · A patient with a persisting memory gap has normal immediate recall, intact distant memories, and preserved general conversation, but cannot learn new information reliably. Why does the preservation of general conversation specifically help rule out dementia?
Illustration
A 57-year-old man with a long history of heavy drinking converses fluently, recognises his surroundings, and can recall childhood events from decades ago in vivid detail, but cannot remember what he had for breakfast an hour earlier or that a doctor had already examined him twice that same morning.
References
- Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 5, 'Disorders of Memory'.