Abstract
Mild cognitive impairment (MCI) may represent a prodromal
phase of dementia and is considered a transitional stage
between normal and pathological aging. The prevalence of MCI
among older individuals in Kerala may be as high as 25%. The
practicing clinician must be aware of the importance of making
an accurate diagnosis of MCI after a focused work up for
reversible aetiologies of cognitive impairment.
Key words: Mild cognitive impairment (MCI), Dementia,
Alzheimer’s disease, Addenbrooke’s Cognitive Examination,
Everyday Ability Scale for India (EASI), acetylcholinesterase
inhibitors
Definition of MCI
The conceptualization of mild cognitive impairment (MCI) as a
diagnostic entity was proposed by Ron Petersen in 1997 to
define a transitional stage in the cognitive continuum from
normal to pathological aging where cognitive impairment is
greater than expected for age, but does not meet criteria for
the diagnosis of dementia [1]. However, even earlier in a
study published in 1988, Barry Reisberg and colleagues at New
York University identified stage-3 on the Global Deterioration
Scale (GDS) of dementia as being indicative of mild cognitive
impairment [2]. MCI is a condition in which individuals
demonstrate cognitive impairment with minimal impairment of
instrumental activities of daily living (IADL). The essential
criteria for definition of MCI are:
1. Cognitive complaint or history of cognitive
decline or impairment
2. Objective evidence of impairment in cognitive domains:
memory, executive function/attention, language, or
visuospatial skills
3. Essentially normal functional activities
4. Absence of dementia
Clinical relevance of MCI
The clinical importance of recognizing MCI and making an
accurate diagnosis in the older patient include:
1. A higher risk of progression to dementia
2. Greater risk of all-cause mortality
3. Opportunity to perform a focused workup for reversible
etiologies of cognitive impairment
4. Enabling the patient to participate in clinical trials
Prevalence of MCI
The American Academy of Neurology (AAN) published an update to
its practice guideline summary on MCI in 2018 and included a
meta-analysis of several studies from around the world,
including India, on the prevalence of MCI [3]. The all-studies
estimate of prevalence of MCI for individuals aged 60–64 years
was 6.7% (95% confidence interval [CI] 3.4%–12.7%); for those
aged 65–69, 8.4% (95% CI 5.2%–13.4%); for ages 70–74, 10.1%
(95% CI 7.5%–13.5%); for ages 75–79, 14.8% (95% CI
10.1%–21.1%); and for ages 80–84, 25.2% (95% CI 16.5%–36.5%).
Assessment of MCI
It is important to establish clinical criteria for definition
of MCI and evaluation of patients using tools and normative
values that are appropriate in the specific population. A few
recent studies from Kerala and other parts of India have
reported on the prevalence rates of MCI among community
dwelling elderly.
Mohan and colleagues reported a cross-sectional study on the
prevalence of MCI among an urban community-dwelling population
aged go years and above in Thiruvananthapuram [4], Kerala. In
this study, the authors defined MCI using the European
Alzheimer’s Disease Consortium criteria and with the specific
instruments outlined below:
1. Cognitive complaints or a reported decline in
cognitive function from the patient or family members.
2. Objective cognitive impairment as evidenced by clinical
evaluation using the Malayalam version of Addenbrooke’s
Cognitive Examination (m-ACE). A score below the cut-off in
at least one of the seven cognitive domains assessed was
defined as the cut-off [One SD below the mean score of the
subject’s educational category was taken as the cut-off for
each domain].
3. Absence of major repercussions on daily life as assessed
by the Everyday Ability Scale for India (EASI). The 95th
percentile of EASI scores of subjects with no subjective or
objective cognitive decline in the study sample was taken as
cut-off. An EASI score up to 2 was taken as evidence of
normal activities of daily living.
4. An absence of dementia as defined by Diagnostic and
Statistical Manual of Mental Disorders (DSM)-IVth
edition i.e. impairments in memory and one additional
cognitive domain causing significant impairment in social or
occupational functioning and representing a significant
decline from previous levels of functioning.
Risk factors for MCI and progression to dementia
This study reported a prevalence of MCI of 26.06%. Some
important co-morbid conditions associated with MCI were a
history of gait imbalance, depression and anxiety. Alcohol
consumption was associated with a higher prevalence of MCI and
current participation in leisure activities (e.g. reading
books/newspapers, participation in games, watching TV,
gardening, listening to music) was associated with a lower
prevalence. While this was a relatively small study enrolling
426 participants, it illustrates the importance of applying
culture-specific criteria and normative scores in screening
older individuals at risk of MCI. Interestingly, the
association between depression and MCI was consistent with an
earlier study from a clinic-based sample from Kerala [5].
Mathuranath and colleagues have done extensive work on
adapting the Addenbrooke's Cognitive Examination (ACE) as a
dementia-screening tool in Kerala and have established that
items in the adapted version are equivalent to that in the
original [6]. Other examples of validated screening tools for
cognitive impairment suitable for use in Kerala include the
Malayalam translation of the 7-minute screen for Alzheimer’s
disease (AD) and the picture-based memory impairment screen
for dementia developed by Verghese and colleagues [7,8].
In a meta-analysis reported in the recent practice parameter
update by the AAN, the cumulative incidence for the
development of dementia in individuals with MCI older than age
65 followed for 2 years was 14.9% (95% CI 11.6%–19.1%).
Compared to age-matched participants, MCI patients 2–5 years
after diagnosis had a higher relative risk (RR) of both
all-cause dementia (3.3; 95% CI 2.5–4.5) and Alzheimer’s
disease (3.0; 95% CI 2.1–4.8) [3].
Practical clinical considerations in evaluating MCI
For patients diagnosed with MCI, clinicians should perform a
medical evaluation for risk factors that are potentially
modifiable eg: sleep apnoea, depression, anticholinergic side
effects of medications, electrolyte disturbances, B
12/folate
levels and syphilis serology if high-risk. The role of
neuroimaging in this clinical setting is to rule out
intracranial space-occupying lesions, multi-infarct/vascular
dementia or other neurodegenerative processes as well as
normal pressure hydrocephalus (NPH). Clinicians should perform
serial assessments over time to monitor for changes in
cognitive status and assess progression of symptoms.
An important consideration for the practicing clinician caring
for an MCI patient is whether to initiate pharmacotherapy with
acetylcholinesterase inhibitors (AChEIs) to reduce the risk of
progression to AD/dementia. Pooled analyses from studies
suggests that there is inadequate evidence to support the use
of these drugs to reduce progression to AD/dementia [3].
References
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