Update on dementia -Part 1: Mild cognitive impairment, screening and diagnostic assessment

Chun-Chung Chan 陳鎮中, Po-Tin Lam 林鈿

HK Pract 2005;27:235-241

Summary

Dementia is common in the elderly. It does not occur de novo but probably represents the end of a spectrum from normal ageing through an intermediate state called mild cognitive impairment. Early identification of mild cognitive impairment and mild dementia is important and clinical criteria and screening tests are readily available for use in daily practice. Primary care physicians should be able to understand that dementia itself is simply a syndromal description and detail portrayal of the profiles of individual patients is essential to plan catered management.

摘要

老人癡呆症是常見的老年疾病。它並非突然發生，而是可能代表了正常衰退過程的尾聲。 中度程度的衰退稱為早期認知障礙。及早發現早期認知障礙及輕度老人癡呆症甚為重要， 日常診症中已有臨床診斷標準及篩選測試方法作為依據。基層醫生應明白，老人癡呆症只是一組綜合症狀的描述， 仔細分析每個病人的情況，是適當診治的必要條件。

Introduction

Dementia is a prevalent disease especially in the elderly population. A recent local study reviewed a prevalence rate of 6.1% among the elderly aged 70 or above.¹ The prevalence doubles every 5 years from age of 65.

Adequate care of dementia patients requires that they be recognized as having memory impairment, identified as having a dementia syndrome, evaluated for the specific cause of the dementia, treated with specific anti-dementia therapies and tackled with the psychosocial aspects of the patients and the caregivers.

It is known that dementia is a neurodegenerative disease representing one end of the spectrum across ageing. An intermediate stage falling in between normal ageing and dementia currently known as mild cognitive impairment (MCI) is getting attention, and many studies are focusing on its importance in terms of conversion and manageability.

It is a common phenomenon that dementia is often under-recognized and under-diagnosed in many areas of the world, including Hong Kong. It is the tradition that decreasing memory in Chinese elders be viewed as an inevitable part of ageing and thus medical attention is often delayed. Moreover, a significant proportion of patients with moderate to severe dementia are unrecognized by primary care physicians as having cognitive impairment.²

Thus, this article will focus on the clinical aspects of mild cognitive impairment, screening for cognitive impairment and diagnostic requirement.

Mild cognitive impairment

MCI is a term commonly defined as a subtle but measurable memory disorder. A person with MCI has cognitive problems, e.g. memory, greater than normally expected with ageing but does not show other symptoms of dementia, e.g. impaired judgement. It may be an intermediate state between ageing and dementia, in particular Alzheimer's disease. Various studies confirmed the increasing risk for developing Alzheimer's disease and less commonly other dementia disorders.^3-8

Compared with the large body of information available about various types of dementia, research about MCI is at a relatively early stage. There are still many unanswered basic questions. It is important to recognize that up till the current state MCI itself is a "work in progress" - the definition, prevalence, dementia conversion rates and types, best assessment methods, investigation modalities, and intervening methods and efficacy are waiting to be clarified.⁹

The most common subtype is called amnestic MCI, for which patients have memory impairment beyond what is expected for age yet other cognitive functions are relatively well preserved. The converting rate to Alzheimer's disease is 12% per year.⁴

The second subtype is named multiple domain MCI, in which patients have impairments in more than one cognitive domain but of insufficient severity to compromise daily functioning or to constitute dementia. The outcome is less defined but probably many will progress to Alzheimer's disease.

The third subtype, single non-memory domain MCI, has the single domain outside of memory being affected. The outcome is dependent on the involved domain, e.g. patients with prominent executive function difficulties may progress to develop fronto-temporal lobe dementia.

The diagnosis of MCI is largely clinical and two commonly used criteria are adopted. According to Petersen's criteria,⁴ a patient with amnestic MCI should have the following features;

1. Subjective memory complaint preferentially corroborated by an informant,
2. Abnormal memory function relative to age and education norms,
3. Essentially normal general cognitive function,
4. Largely normal activities of daily living, and
5. Not demented.

Another diagnostic criteria by Flicker et al.⁵ (1991) was based on ratings on a global clinical staging scale called Global Deterioration Scale.10 Patients having the following clinical features are classified as in stage three of the scale which is equivalent to MCI;

1. Manifestations in more than one of the following areas;
1. patient may have gotten lost when travelling to an unfamiliar location;
2. co-workers become aware of patient's relatively poor performance;
3. word and name finding deficit becomes evident to intimates;
4. patient may read a passage or a book and retain relatively little material;
5. patient may demonstrate decreased ability in remembering names upon introduction to new people;
6. patient may have lost or misplaced an object of value;
7. concentration deficit may be evident on clinical testing.
2. Objective evidence of memory deficit obtained only with an intensive interview.
3. Decreased performance in demanding employment and social settings.
4. Common activities of daily living are intact, but there may be subtle impairment in very complex activities of daily living.

As there is a lack of agreement about a definition, any two individuals with a diagnosis of MCI may have relatively different symptomatology. Thus, treatment recommendation by clinicians will also vary. There is currently no evidence-based treatment for MCI and there is not enough evidence to recommend a standard management approach. Multiple therapeutic approaches are being considered including cholinesterase inhibitors, antioxidants, anti-inflammatories. Recently, donepezil, an anti-cholinesterase, is shown to delay the progression to Alzheimer's disease from MCI by six months.¹¹ On the other hand, two clinical trials showed a larger number of deaths without any significant improvement on cognition in participants receiving galantamine, another anti-cholinesterase, than in those receiving a placebo.¹² Further studies are required before we can have any definitive intervention for MCI.

Screening

1. Ten warning signs
   

   Formal assessment of cognitive function is the backbone of a good geriatrics assessment because of the high prevalence and social costs of dementia in later life and the emergence of pharmacological therapies.¹³ However, due to time constraint, it is difficult to perform screening test on all elderly patients coming to the office. Thus, particular attention to the presence of warning signs¹⁴ suggestive of cognitive impairment is a useful adjunct to maximize the gain;

   1. Forgetfulness with effects at work, e.g. forget names and appointments,
   2. Difficulties with familiar activities, e.g. housewife to prepare a meal,
   3. Language problems, e.g. difficulty finding right words,
   4. Problems with spatial and temporal orientation, e.g. get lost at familiar place,
   5. Impaired capacity of judgement, e.g. wear inappropriate clothings,
   6. Problems with abstract thinking, e.g. simple calculations in the market,
   7. Leaving things behind,
   8. Mood swings and behavioural changes, e.g. sudden mood swing without discernible cause,
   9. Personality change, e.g. a friendly person becomes unexpectedly angry, jealous,
   10. Loss of initiative, e.g. lose interest in hobbies.

2. Screening instruments
   

   There are many screening tests available that can help to sort out those who should have further detailed assessment. However, no single screening test has been shown to pass all the relevant performance tests needed to include it in a guidance level recommendation.

   Mini-Mental State Examination

   Mini-Mental State Examination (MMSE) is the most commonly used and is considered the "gold-standard" screening method. A Chinese version (C-MMSE) is available and validated in the local setting with good sensitivity (97.5%) and specificity (97.3%).¹⁵ Although the MMSE is relatively easy to administer and has good inter-rater reliability, sensitivity and specificity, it requires at least five minutes to complete, provided that the patient is cooperative. This may not be time-effective for a busy primary care clinic. Although it is shown not educationally biased with respect to the item characteristics, reliability and construct validity, its predictive validity as a screening test for dementia is educationally biased.¹⁶ In order to eliminate such bias, a two point higher cut off score for the subjects whose education extends beyond certain level is required.

   Another important limitation is that there is an overemphasis on orientation and language related functions whereas other cognitive domains, such as executive function and constructional abilities, that may be impaired in early stage of dementia are neglected.

   Clock-Drawing Test

   For decades, clock-drawing tasks (CDT) have been used to assess the mental status of patients with various neurologic or psychiatric disorders. They are widely accepted cognitive screening tools despite the lack of a single standard for administration or scoring.

   The major strength of the test is its ability to reflect in composite form the intactness of many interdependent cognitive functions _ namely long term memory, auditory processing, strategy planning, visual memory and reconstruction, visual-spatial function, motor programming and execution, numerical knowledge, abstract thinking, concentration, frustration tolerance, and inhibition of impulsive responding and of the tendency to be pulled astray by perceptual features.¹⁷

   Lam has derived a scoring method which was validated in Chinese elderly adults (Table 1, Figure 1).¹⁸ At a cut-off point of 3/4, the test had a sensitivity of 83% and specificity of 79%. Previous studies have examined the effect of mental disorders on the performance of the CDT. Depression at late life is not an uncommon condition in daily practice. It was shown that it did not alter the specificity of the test on dementia screening.^19,20

   Abbreviated Mental Test

   The Abbreviated Mental Test (AMT) is a useful screening test for abnormal cognitive function in the elderly patient because of its simplicity. A modified local version was developed and validated (Figure 2).²¹ The cut-off point of six (below six was considered abnormal) yielded a sensitivity of 96% and a specificity of 94%.

3. Choice of instrument
   

   The choice of screening tests depends on a number of factors. Firstly, the familiarity of the tests is of utmost importance to reduce add-on false positive and false negative rates. Secondly, timing allowed is also important. A recent local study has shown that CDT takes significantly less time to complete than MMSE yet attaining only slightly lower sensitivity.²² AMT probably requires the least time to complete when comparing with CDT and MMSE while maintaining a satisfactory sensitivity. Last but not least, patient acceptance can affect the cooperativeness and accuracy of the results. Many patients with early dementia become very suspicious and defensive about answering some of the questions in the test. As a result, the assessment may be incomplete or may even lead to some compromise of the relationship between the clinician and the patient.

Diagnostic requirement

Dementia by itself is not a diagnosis. It is a syndromal disorder signifying significant impairment in various aspects of cognition leading to functional disability. Thus, assessment should include history taking especially with attention to salient features, focused physical examination with demonstration of significant positive and negative signs, functional assessment including basic and instrumental activities of daily livings, neuro-psychiatric assessment revealing the presence and severity of the behavioural and psychological symptoms of dementia (BPSD), and appropriate investigations including structural imaging(Table 2).

A complete diagnosis for a patient with dementia should comprise of the followings;

1. Confirmation of dementia syndrome according to DSM-IV²³ or ICD-10²⁴ criteria: impairment in memory together with at least one more aspect of cognition, significant enough to impose function disability, lasting for longer than 6 months, with preservation of environmental awareness,
2. Subtype of the dementia, e.g. Alzheimer's disease, vascular dementia, dementia with Lewy bodies, etc.,
3. Severity of the dementia, based on symptomatology and functional disbility: the score of MMSE can be a rough guide to the extent of severity,
4. Presence and severity of BPSD,
5. Caregiver status: caregiver is an important aspect in management of dementia, caregiver stress and burden can significantly affect the provision of quality care.

Conclusion

Management of dementia requires prompt and careful identification. Awareness of the pre-dementia condition of MCI can prompt the patient to regular surveillance and early initiation of treatment when evidence of dementia is present. Various useful screening tests are handy to use with satisfactory sensitivity and specificity. A complete description of the dementia syndrome in every particular patient is important with regard to management and prognosis predication.

Key messages

1. Mild cognitive impairment is defined as a subtle but measurable cognitive disorder and it carries increased risk for developing various types of dementia.
2. Attention to warning signs suggestive of cognitive impairment is important to identify high risk elders for further assessment.
3. Screening instruments including C-MMSE, CDT and AMT are handy and validated for local use.
4. Dementia is not a diagnosis but a syndromal disorder. Each patient with dementia should undergo a detailed assessment process to ascertain the subtype, severity, presence of BPSD and caregiver status.