Abstract & Commentary
Source: Powlishta KK, et al. The clock drawing test is a poor screen for very mild dementia. Neurology. 2002;59:898-903.
The clock drawing test is used by many physicians and other health professionals to rapidly detect signs of cognitive impairment. This test involves asking the patient to draw the face of an analog clock, fill in all the numbers, and set the hands to a fixed time. The Clock Drawing Test can be rapidly administered, scored in a quantifiable way, and is sensitive to deficits in a variety of cognitive domains. Although past studies have shown that the Clock Drawing Test is frequently abnormal in patients with mild dementia associated with Alzheimer’s disease (AD), few studies have examined its usefulness in detecting the very earliest signs of dementia. In a longitudinal study of 75 patients that included 25 with the earliest detectable stage of dementia, Powlishta and colleagues found that clock drawing had unacceptably low sensitivity in detecting the very earliest stages of AD.
In this study, 6 different scoring systems for the Clock Drawing Test were compared. Good inter-rater reliability (91-97%) was found among all 6 scoring systems. Powlishta et al examined the performance on clock drawing as a function of dementia severity as measured by the Clinical Dementia Rating (CDR) scale. While 80-97% of patients with mild dementia (CDR = 1) scored abnormally on the Clock Drawing Test, only 20-60% of those with very mild impairment (CDR = 0.5) scored below the cutoffs for normal. The Mendez scoring system had the best sensitivity for very mild impairment but had the lowest (60%) specificity.
Powlishta et al emphasize that clock drawing should not be used in isolation when screen for the earliest signs of AD. Instead, diagnosis requires a thorough clinical assessment that incorporates medical assessment, multiple measures of cognition, and a careful history from a collateral source.
Clock drawing is an appealing cognitive screening test in many respects. It is quick and easy to administer, easy to score, and results can generally be reproduced across examiners and multiple test sessions. Results correlate reasonably well with the Folstein Minimental State Examination in selected patient populations. The pattern of deficits found on clock drawing often provides valuable clues to the nature of the cognitive domains impaired by a variety of brain disorders. For example, the clocks drawn in the context of visuospatial impairments may be distinctly different from those produced by patients with executive dysfunction or memory loss as their primary deficits.
As with all brief cognitive tests, clock drawing has its limitations. This particular study examined a relatively small number of cases and used published cutoffs for distinguishing normal from demented cases. Unfortunately, it did not use a Receiver Operating Characteristic (ROC) analysis to evaluate which scoring system and cutoff values provide optimal sensitivity and specificity in detecting very mild dementia. Nevertheless, the results suggest that impaired performance on clock drawing is a useful correlate of frank dementia in conditions such as AD but may not be sensitive enough to detect the very mildest cases. A recent study suggests that Mild Cognitive Impairment (MCI) may be detectable by repeatedly performing a small set of computerized cognitive tests over a single day.1 Until such approaches are validated, MCI is best identified through the use of sensitive tests of memory, particularly delayed recall, coupled with other cognitive measures and information culled from interviews with the patient and a knowledgeable informant. Clock drawing still has a place in screening for dementia but should not be used in isolation when screening for very mild cognitive deficits. — Norman R. Relkin
Dr. Relkin, Associate Professor of Clinical Neurology and Neuroscience, New York Presbyterian Hospital-Cornell Campus, is Assistant Editor of Neurology Alert.
1. Darby D, et al. Neurology. 2002;59:1042-1046.