CHAPTER 26: MINI-COG EXAM/CLOCK DRAWING TEST (CDT)

Description

The Mini-Cog is a quick screen for cognitive impairment that comprises two parts: a three-word registration and recall where the person is told three words that they must recall at a later time (0 to 2 points) and a clock-drawing task (0 or 2 points). The Mini-Cog can be completed in less than 5 minutes (less than 3-minutes in certain populations); thus, it can be effective in identifying those who require further investigation into their clinical presentation in fast paced settings such as emergency rooms or other settings that are time dependent (Thompson, 2008). During administration, the client is first asked to repeat three unrelated words, such as penny, apple, and chair, then he or she is asked to draw a clock with two hands denoting a specific time. The subject is then scored on his or her ability to complete each task where scores of 0, 1, or 2 denote probable impairment and 3, 4, or 5 indicate impairment is less likely.

Psychometrics

Research by the screen’s creators found that when scores of those with “possible cognitive impairment” or “probably normal” were compared to the Mini Mental State Exam’s (MMSE) cutoff score of 25, both batteries had similar sensitivity (0.76 vs 0.79) and specificity of 0.89 vs 0.88 (Borson, Scanlon, Chen, & Ganguli, 2003). Scores for both the Mini-Cog and MMSE were found to be comparable with that achieved using conventional neuropsychological batteries (0.75 sensitivity and 0.90 specificity) as well (Borson et al., 2003). A subsequent study, also by its creators, found that the Mini-Cog fared slightly better than the MMSE in accurately classifying impaired individuals at 83% for the Mini-Cog and 81% for the MMSE. The Mini-Cog was also found to be better at recognizing persons with neurocognitive disorders (NCD) of the Alzheimer type as opposed to other types such as Lewy body or vascular type. Costa, Severo, Fraga, and Barros (2012) had somewhat different results in their sample of 609 community dwelling Portuguese adults aged 60 years and over where they found that an MMSE cutoff score of 25 (6.2%) was considered impaired, whereas the Mini-Cog (at a cutoff score of 3) detected impairment in 11.3% of the sample. Research by Doerflinger (2007) found the Mini-Cog to have a sensitivity in detecting cognitive impairment ranging from 0.76 to 0.99, and specificity ranging from 0.89 to 0.93 at the 95% confidence interval. A chi square test, which investigates the distribution of categorical variables, was reported at 234.4 for NCD of the Alzheimer’s type and 118.3 for other NCD dementias, further highlighting its particular ability to detect NCD of the Alzheimer’s type.

Advantages

The Mini-Cog is a simple screen that has a high sensitivity and acceptable specificity in the general practice setting (Kamenski et al., 2009). There is also evidence to suggest that the Mini-Cog has good predictive value in multiple clinical settings (Borson, Scanlan, Brush, Vitallano, & Dokmak, 2000; Borson et al, 2003). It is a quick screen (< 5 minutes to administer) and no training is needed. The assessment may be less stressful to clients than other longer mental status tests and when compared to the MMSE (which is arguably the gold standard), it showed close agreement with regard to sensitivity and negative predictive value, thus making the Mini-Cog a viable fast screen to decide if further testing is warranted (Doerflinger, 2007).

Disadvantages

Scoring for the CDT section can be difficult and is dependent on skilled observation; thus standardization of scoring could be somewhat problematic as it relies on a clinician’s individual interpretation of a drawn clock which can be abundant. One study evaluating Mini-Cog cultural heterogeneity found that both its sensitivity (0.63) and specificity (0.59) were low among subjects with < 5 years of formal education when compared to subjects with 5 to 8 years of formal education where accuracy was better (Borson & Scanlan, 2006).

Administration

The Mini-Cog is composed of an interactive memory recall section in which a person is asked to recall three unrelated items. The client is then asked to complete a drawing-based activity in which a person is asked to draw a clock. The cumulative score is calculated by summing each item score where the test’s maximum score is 5. A score of 0, 1, or 2 is suggestive of probable impairment and scores of 3, 4, or 5 suggests cognitive impairment is less likely.

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