Memory Impairment

I. Background
Memory impairment refers to the inability to learn new information or recall previously learned information. It can be a component of delirium when accompanied by an altered level of consciousness (see Chapter 4.3) or a component of dementia in patients with disturbances in behavior, other cognitive functions, and independence (see Chapter 4.4). There is a normal cognitive decline with aging that consists of a stable mild memory loss and a decline in the rate of processing new information. This normal cognitive decline does not progress to the point of affecting daily function.
II. Pathophysiology
A. Etiology
  • Memory disorders without delirium or dementia are called amnestic disorders. They are usually due to the effects of other medical conditions, medications, toxins, or drugs of abuse (1). Often there is a period of delirium that precedes amnestic disorders. For example, infectious encephalitis and alcohol use can both cause an initial period of delirium followed by memory problems, which remain after the level of consciousness has returned to normal.
  • Memory disturbance can be caused by physical trauma such as head injury or emotional trauma, which may cause a rare, but dramatic presentation with one of the dissociative psychiatric disorders, such as a conversion reaction or fugue state (1).
  • Mild cognitive impairment (MCI) is the term used for memory loss that is more than is usual with normal aging, but does not meet the criteria for dementia. MCI is characterized by increasing difficulty with memory and progressive decline, while maintaining other cognitive functions and activities of daily living (2). As the definitive criteria for this term improves, it may become a more useful clinical predictor of progression to dementia.
B. Epidemiology
It is difficult to quantify the prevalence of MCI because the criteria are not uniform, and many patients may not seek professional care. Patients with MCI may progress to dementia at a rate that is four times higher than that of normal peers, although there are limited studies to help identify who is likely to progress (3). The prevalence of pure amnestic syndromes depends on the etiology, but they are not as common as dementias, which are discussed in Chapter 4.4.
III. Evaluation
A. History
The history should initially focus on ruling out dementia and delirium. Careful drug history must include over-the-counter medicines, which may have central nervous system side effects. It is important to obtain corroborating history from family also. Patients with dementia are often brought in by relatives who are concerned about their function, but the patients have poor insight into their own deficits. These patients are different from patients with normal age related cognitive decline, MCI, or depression who will often complain about their own forgetfulness.
B. Physical examination
A complete physical examination, including a neurologic examination, should be performed.
  • A Mini-Mental State Examination (MMSE) takes only a few minutes to perform. It can help identify memory deficits as well as discern non-memory cognitive problems, which aids in differential diagnosis (4). Patients with depression may score well or may show poor effort rather than give incorrect answers. Patients with dissociative disorders may be able to score well as their memory loss may only be for a specific time or situation. If cognitive deficits other than memory are found, dementia must be strongly considered. A score of 24/30 points or greater is considered normal, but may be adjusted for age or educational level. A copy of the and a discussion of the scoring norms as they relate to age and education level is available on-line at http://www.aafp.org/afp/20010215/703.html (5).
  • Instructions for performing the MMSE:
    • Orientation to time First, ask the patient the day, date, month, year, and season. The maximum score is 5.
    • Orientation to place Second, ask the patient what building, town, county, state, and country they are in. The maximum score is 5.
    • Memory registration Say the name of three objects (e.g., cup, flag, door), and ask the patient to repeat them. If they miss any, continue until they are able to repeat the words so that recall can be tested later. The maximum score of 3 is based on the first trial.
    • Attention Ask the patient to spell the word “world” backwards or to subtract 7 from 100 serially backwards (stop after five answers). The maximum score is 5.
    • Memory recall Ask the patient to remember the three objects from the registration portion of the test. The maximum score is 3.
    • Language
      • Agnosia Show the patient a pencil and ask them to identify the object. The maximum score is 2.
      • Aphasia Ask the patient to repeat the phrase “no ifs, ands, or buts.” Any mistake or starting over on the first try scores 0. The maximum score is 1.
      • Aphasia Write the phrase “close your eyes” on a blank sheet of paper. Ask the patient to read and obey the command. The maximum score is 1.
      • Apraxia Ask the patient to follow a 3-step command. “Pick up this paper with your right hand, fold it in half, and place it on the floor.” The maximum score is 3.
      • Agraphia Ask the patient to write a sentence. It must have a subject and a verb and make sense. The maximum score is 1.
    • Visual-spatial awareness Ask the patient to copy a set of interlocking pentagons. All ten angles must be present, and one angle of each figure should intersect with the other figure. The maximum score is 1.
C. Testing
There are no specific laboratory tests for memory impairment. Any tests should be used to confirm or rule out suspected medical causes of amnestic disorders. If early dementia or delirium is suspected, the workup can be found in Chapters 4.3 or 4.4.
D. Genetics
A family history may uncover a predilection for substance abuse, depression, or a dementia syndrome. There are no specific genetic tests for disorders of memory impairment. Genetic testing is investigational for a number of dementia syndromes including Alzheimer's dementia, but none is currently recommended for clinical use.
IV. Diagnosis
A. Differential diagnosis
  • Normal age related cognitive decline does not progress over time to impair daily function. Ask about the onset and course of the problem and follow serial cognitive function testing when in doubt.
  • Dementia syndromes include memory impairment, but must also affect other cognitive functions to the extent that activities of daily living are progressively impaired (see Chapter 4.4).
  • Delirium must be considered if the patient's level of consciousness is affected (see Chapter 4.3).
  • Pseudodementia is seen with depression. Patients may show poor effort on cognitive testing as opposed to incorrect answers. A formal depression screen may be helpful.
  • Malingering or factitious disorder may present as memory impairment in the right social or work setting. Formal cognitive testing may reveal inconsistent deficits.
B. Clinical manifestations
Memory impairment most commonly presents with a patient complaining of normal age related cognitive decline or MCI if it is progressive. Memory loss may persist after an identified illness, trauma, or intoxication. A
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patient will rarely present with a dissociative disorder in which specific memories are lost, whereas cognitive testing usually remains normal.
References
1. American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 4th ed. Washington, DC: APA Press, 1994.
2. Winblad B, Palmer K, Kivipelto M, et al. Mild cognitive impairment - beyond controversies, towards a consensus: report of the International Working Group on Mild Cognitive Impairment. J Intern Med 2004;256(3):240 - 246.
3. Ganguli M, Dodge HH, Shen C, et al. Mild cognitive impairment, amnestic type: an epidemiologic study. Neurology 2004;63:115.
4. Folstein MF, Folstein SE, McHugh PR. “Mini-mental state”: a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 1975;12:196 - 198.
5. Santacruz KS, Swagerty D. Early diagnosis of dementia. Am Fam Physician 2001;63(4):620 - 626.