Clock test deficits related to the global cognitive state in Alzheimer's and Parkinson's disease

Clock drawing (CD) seems to be impaired quite early in the process of cognitive decline in Parkinson's disease (PD).

We assessed performance on the CD test (CDT), clock setting test (CST) and clock reading test (CRT) in 32 elderly healthy controls, 41 patients with PD, 23 patients with amnestic mild cognitive impairment (aMCI) and 40 patients with Alzheimer's dementia (AD). Our focus was on comparing the performance of PD and aMCI/AD patients in relation to their global cognitive states (operationalized by the Mini Mental Status Examination). We also analyzed qualitative differences in errors of drawing, setting and reading clocks.

We found that performance in CDT, but not in the CST or CRT, was impaired earlier in PD than in aMCI/AD. Incorrect placement of the minute hand was the most prominent error in both patient groups. We found no specific influence of visuospatial dysfunction in PD on clock drawing.

Our findings suggest that executive function related to retrieval of semantic memory about the minute hand is compromised early in PD.