How to avoid 3 common errors in dementia screening

Treatment options for dementia are expanding and improving, giving extra impetus to detecting this progressive disease as early as possible. For example, research on the cholinesterase inhibitor donepezil has shown it can delay cognitive decline by 6 months or more compared with controls^1,2 and possibly postpone institutionalization. With the number of elderly individuals and cases of dementia projected to grow significantly over the next 20 years,³ primary care physicians will increasingly be screening for cognitive impairment. Given the time constraints and patient loads in today’s practices, it’s not surprising that physicians tend to use evaluation tools that are brief and simple to administer. However, there are also serious pitfalls in the use of these tools.

When to screen. Many health-related organizations address screening for dementia^4,5 and offer screening criteria (eg, the Alzheimer’s Association,⁶ the US Preventive Services Task Force⁷). Our experience suggests that specific behavioral changes are reasonable indicators of suspected dementia that should prompt cognitive screening. Using the Kingston Standardized Behavioural Assessment,⁸ we demonstrated a consistent pattern of earliest behavior change in a community-dwelling group with dementia.⁹ Meaningful clues are a decreased ability to engage in specific functional activities (including participation in favorite pastimes, ability to eat properly if left to prepare one’s own food, handling of personal finances, word finding, and reading) and unsteadiness. These specific behavioral changes reported by family or a caregiver suggest the need for cognitive screening.

Pitfalls associated with common screening tools, if not taken into account, can seriously limit the usefulness of information gained during assessment and potentially lead to a wrong conclusion. Screening tools are just that: a means of detecting the possible existence of a condition. Results are based on probability and subject to error. Therefore, a single test score is insufficient to render a diagnosis of dementia, and is one variable in a set of diagnostic criteria.

The purpose of this article is to review some of the most commonly used tools and procedures for dementia screening, identify procedural or interpretive errors made in everyday clinical practice, and suggest practical yet simple strategies to address these problems and improve the accuracy of assessments. We illustrate key points with clinical examples and vignettes using the Mini-Mental State Examination (MMSE),¹⁰ an Animal Naming Task, and the Trail Making Test.¹¹

Common error #1: Reliance
 on simple, single cutoff scores


There are a number of important considerations to keep in mind when trying to make sense of scores from the many available cognitive tests.

Though a score of ≥24 on the MMSE is commonly used to rule out dementia, that cutoff misses true impairment in many patients.The range of normal test results is wide. The normal range for most physiologic measures, such as glucose levels or hemoglobin counts, is relatively narrow. However, human cognitive functions can naturally differ from person to person, and the range of normal can be extremely large.

A single, all-purpose cutoff score ignores critical factors. Very often, clinicians have dealt with the issue of wide variance in cognition scores by establishing a general cutoff point to serve as a pass-fail mark. But this practice can result in both under- and overidentification of dementia, and it ignores the 2 components that chiefly determine how individuals differ cognitively: age and intelligence.

Practical fix: Use age-, intelligence-corrected normative data


Level of cognitive performance can be revealing when adjustments are made for age and intelligence. Not taking these factors into account can lead to many errors in clinical decision making.

Age matters. Many cognitive capacities decline as part of normal aging even in otherwise healthy individuals (eg, reaction time, spatial abilities, flexibility in novel problem solving).¹² With this in mind, psychologists often have made the distinction between “hold” tests (remaining stable or even improving with age) and “no-hold” tests (declining with age).¹³ Therefore it is critical to ask, “What is normal, given a particular patient’s age?” If normative data corrected for age are available for a given test, use them.

Intelligence is a factor, too. Intelligence, like most human qualities, is distributed along a bell-shaped curve of normal distribution, wherein most people fall somewhere in the middle and a smaller number will be at the lower and higher tails of the curve. Not all of us fall into the average range of intelligence; indeed, psychometrically, only half of us do. The other half are found somewhere in the more extreme ends. In evaluating a person for dementia, it is critical to compare test results with those found in the appropriate intellectual group. But how does the physician looking for a brief assessment strategy determine a patient’s premorbid level of intellectual functioning?