A simple scoring system for clock drawing in patients with Alzheimer's disease.

Abstract

To the Editor: Visuospatial skills are commonly impaired in patients with Alzheimer's Disease.1,2 Thus, the Clock Drawing Test is used widely for assessing visuospatial skills in patients with dementia.3–5 Many scoring systems have been developed for the clock test.4,5 Its effectiveness as a screening tool for the diagnosis of dementia has been well tested.4–6 Many previous studies have demonstrated good correlation between the clock test score and the Mini-Mental State Exam (MMSE).2,3,5,6 We present a new clock scoring system, which we refer to as the “simple scoring system,” and compare it with a previously published scoring system by Sunderland et al.4 We evaluated retrospectively charts of 88 patients having the diagnosis of probable Alzheimer's disease. All patients met NINCDS-ADRDA(II) criteria for Alzheimer's Disease. As part of the initial evaluation process, all patients were also tested with the MMSE and were asked to draw a clock indicating the time of 2:45. The clock circle was not predrawn. Mean age of the 88 patients in the study was 77. Mean MMSE score was 14. Male/female ratio was 2:3. The MMSE was performed by an RN; both clock scoring systems were performed by a medical resident who was unaware of the MMSE score. There was no statistical difference between the two scoring systems with respect to age, sex, and race. There was a good correlation between the “simple score system” and the MMSE (r = .57). A statistically significant correlation occurred between the standard score system and the MMSE (r = .55). There was also a strong correlation between the standard score and the simple score systems (Pearson's correlation coefficient r = .91, P < .001, with 95% confidence limits: 0.86 < r < .94). When both scoring systems were considered in a multivariate linear regression analysis, only the “simple scoring system” was found to be a significant predictor of the actual MMSE (P < .01). Using simple linear regression, we found the following formula to best approximate the MMSE score in patients with the diagnosis of probable Alzheimer's Disease: MMSE = 2.4 (Clock Score) + 12.7 (P < .001) (1) The formula correlates to MMSE scores between 13 and 27. A clock score of zero predicts a MMSE score of 13 and below. A clock score of 6 correlates with a MMSE of 27 and higher. The “simple clock score system” is a short, logical scoring system, easy to remember and to administer. Compared with previous published scoring systems, it not only has a high correlation with the MMSE, but it can also predict the MMSE score.