Longitudinal changes in clock drawing test (CDT) performance according to dementia subtypes and severity

The CDT requires a patient to draw the face of a clock, insert all the numbers and set the hands for a specified time. This task engages a number of cognitive abilities including verbal understanding, memory, spatially coded knowledge, planning, concentration and visuoconstructive skills. Although CDT has been regarded as a simple and useful screening tool in dementia, little is known about the longitudinal changes in CDT performance and error types, according to dementia subtypes and their severity.

Two hundred thirty-five consecutive patients with dementia (Alzheimer disease = AD, n=94, Parkinson's disease with dementia (PDD), n = 119, Vascular dementia = VaD, n = 22) were recruited from the memory clinic at Chungnam University hospital from January 2005 to July 2009. The Korean version of the mini-mental state examination (MMSE-K) and CDT were performed by all participants every 6 months. Scoring of the CDT performance was in accordance with the method of Mano and Wu. Error types of CDT were classified as follows: stimulus-bound response (SBR), conceptual deficit (CD), spatial and/or planning deficit (SPD) and perseveration error (PE). We divided patients into 3 groups by their initial MMSE-K score (severe, MMSE-K ≤ 17; moderate, 18 ≤ MMSE-K < 24; mild, 24 ≤ MMSE-K). Comparisons of CDT scores and error types in the three dementia subtypes and three cognitive groups were conducted.

Longitudinal changes on CDT and MMSE-K scores were not different between the three dementia subtypes. From the analysis of CDT error type, the most common error type was SPD in patients with mild to moderate dementia. In contrast, CD error was the most frequent in severe dementia group. The order of error frequency in all subjects from baseline to the last follow-up was as follows: SPD, CD, SBR and PE except CD was the most frequent error type in AD patients after 18 months from baseline.

Longitudinal analysis of error on CDT may reflect different characteristics of cognitive deterioration according to dementia subtypes and dementia stages.