Applied Evidence

What’s causing my older patient’s cognitive decline?

J Fam Pract. 2017 November;66(11):670-676

From The Journal of Family Practice | 2017;66(11):670-676.

References

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In the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM V), this concept is identified as mild neurocognitive disorder, with the additional caveats that an individual’s cognitive deficits do not occur exclusively in the context of delirium and are not better explained by another mental disorder such as depression or schizophrenia.⁹

An accurate assessment of cognitive change is best measured against the individual’s baseline, which may necessitate the report of a reliable acquaintance. An assessment of functional abilities is also critical. Mild problems in performing complex functions (bill paying, shopping, etc) could be present and still allow a patient to meet the criteria for MCI. An individual may take more time, be less efficient, or make more errors than before; however, independence with minimal aid or assistance is preserved. It can be difficult to distinguish MCI from the effects of normal aging particularly on a single assessment, and serial evaluations can be beneficial.

MCI can be divided into 4 subtypes depending upon the cognitive domains affected (complex attention, executive function, learning and memory, language, visuospatial, social cognition):

Amnestic MCI single domain, if only memory is affected.
Amnestic MCI multiple domain, if memory and any other cognitive domains are affected.
Non-amnestic MCI single domain, if any other cognitive domain aside from memory is the only one affected.
Non-amnestic MCI multiple domain, if multiple domains other than memory are affected.

These distinctions may provide clues to the underlying cause of dysfunction and provide prognostic information regarding the risk of progression to dementia.^6,7

Prevalence estimates for MCI vary widely due to differences in definitions used and populations studied. The best estimate is 5% to 10% prevalence among those ages 65 to 69 years old, and 12% to 25% among those ages 80 to 84.¹⁰ Similarly, estimates of the rate of progression to dementia vary. Among MCI populations identified through referral sources such as memory centers, the rate of progression to dementia has been 10% to 15% per year.¹¹ In epidemiologic studies of general populations, the rate has been 6% to 10% per year.¹¹ The rate of development of dementia among normal subjects is 1% to 2% per year.⁵

Dementia/major neurocognitive disorder

The primary feature distinguishing MCI/mild neurocognitive disorder from dementia or major neurocognitive disorder is a patient’s functional status. The core clinical criteria for all-cause dementia are cognitive or neurobehavioral symptoms that:¹²

interfere with work or usual daily function,
represent a change from the prior baseline function,
are not explained by delirium or a psychiatric illness, and
include detectable impairment in 2 cognitive domains.

Criteria outlined in the DSM-V for major neurocognitive disorder are essentially the same but describe the functional change criteria as cognitive changes that “interfere with independence in everyday activities.”⁹ The DSM-V elaborates: “at a minimum, requiring assistance with complex instrumental activities of daily living such as paying bills or managing medications.”

Assessing functional status accurately in clinical practice typically requires the assistance of a collateral informant who knows the patient well. The Informant Questionnaire on Cognitive Decline in the Elderly (https://www.alz.org/documents_custom/shortiqcode_english.pdf) is one validated assessment tool that can be used for this purpose.¹³ With this self-administered form, the informant answers 16 questions regarding changes in the patient’s performance of different activities over the 10 years prior. Alternatively, a structured interview based on indices of activities of daily living (ADLs) and instrumental activities of daily living (IADLs) as listed in TABLE 1 can be employed.^14,15

Review of the various causes of dementia is beyond the scope of this article, but a list of common diagnoses is presented in TABLE 2.

Dementia syndrome of depression (pseudodementia)

Elderly patients with depression commonly complain of memory impairment, and this interaction between depression and dementia has been investigated for decades. The term “pseudodementia” has been used since 1961 to describe signs of dementia in a patient with any psychiatric illness,¹⁶ but it has since been refined to apply solely to depression. The prevalence of depression among older adults varies depending on the population studied and how depression is defined. Approximately 2% to 3% of community-dwelling elders meet criteria for major depression, with 10% to 30% showing some symptoms of depression.^17,18

Twenty percent to 40% of elderly patients diagnosed with depression will have evidence of cognitive impairment.

Twenty percent to 40% of elderly patients diagnosed with depression will have evidence of cognitive impairment.^19-21 Most improve with antidepressive treatment, though evidence of cognitive impairment may continue for some.¹⁹

A broad range of cognitive deficits have been associated with depression. Most consistently described are deficits in processing speed,^22-25 attention,^26-28 and executive function.^22,25-29 Memory deficits can be apparent with tests of delayed recall, but recognition (the ability to identify items from a list) generally is preserved.^26,28-30

Distinguishing mild cognitive impairment from normal effects of aging may require serial evaluations following an initial assessment.

Distinguishing between pseudodementia and true dementia can be challenging. An increased severity of deficits, particularly with delayed recall, is more indicative of dementia.³¹ Additionally, on clock drawing tasks, individuals with depression perform more comparably to controls than do those with true dementia.³²

A 2013 meta-analysis reported a significant association of late-life depression with subsequent development of dementia, with an odds ratio (OR) of 1.85. The risk of subsequently developing vascular dementia (OR=2.52) was significantly higher than that for Alzheimer’s disease (OR=1.65). Individuals with evidence of reversible cognitive impairment at the time of diagnosis of depression seem to be particularly vulnerable, with dementia developing in 43% to 71%, compared with rates of 12% to 18% among elders diagnosed with depression but lacking signs of cognitive impairment.^20,21