Clock Drawing Test (CDT): is Qualitative Analysis of the CDT Better to Screen Mild Cognitive Impairment than Quantitative Analysis?

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Background: Mild cognitive impairment (MCI) was originally used to describe a transitional state between normal condition and dementia. Revised and extended definition of MCI has been proposed that covers a broader range of cognitive impairment, distinct from normal ageing and from Alzheimer’s disease. Despite the existence of reports regarding analyses of the Clock Drawing test (CDT) in Alzheimer’s disease and vascular dementia, those focusing on MCI subjects are still lacking. The purpose of this study was to assess the characteristics of CDT and compare the results of quantitative and qualitative analyses of CDT performance in patients with MCI. Materials and methods: Five hundred four consecutive patients with MCI (Korean versions of the Mini-Mental State Examination (K-MMSE)>23) were recruited for the study. All participants were examined by the K-MMSE, modified-MMSE (3MS) and the CDT. Quantitative scoring of the CDT was done by the Manos and Wu’s method. Qualitative error types of the CDT were classified as stimulus-bound response (SBR), conceptual deficit (CD), spatial and/or planning deficit (SPD), and perseveration error (PE) by Rouleau’s classification. We divided the subjects into two subgroups by the MMSE scores (lower cognitive function group, MMSE=24~26 vs. higher cognitive function group, MMSE=27~30) and compared the CDT scores and frequency of the error types between them. Results: The total scores in the CDT significantly correlated with the total scores of the K-MMSE, 3MS and the level of education. Of the errors in the CDT, SPD was the most frequent type of error (45.3%) in the total samples. The scores in the K-MMSE and 3MS in the patients having CD errors were lower compared with those of other types of error. The lower cognitive group made more CD error (32.9%) than that of the higher cognitive group (25.5%). Conclusion: Although the CDT cannot be used solely for clinical diagnosis of dementia, it provides useful cognitive information quantitative as well as qualitative ways, estimating the characteristics of MCI patients as a simple screening test.