Validation studies of the clock drawing test in mild cognitive impairment

Abstract

Introduction: Mild Cognitive Impairment (MCI) is a transitional entity between normal aging and Alzheimer’s disease. It is assumed that an early identification and intervention in MCI may delay or slow its progression to dementia and several neuropsychological brief-tests have been investigated in this context. The Clock Drawing Test (CDT) is a widely used instrument in this field; however, its application needs further validation in specific clinical populations, mainly in milder forms of cognitive decline and in the distinction between MCI subtypes. Objectives: To validate three scoring systems of the CDT for the detection of cognitive impairment in a cohort of MCI-patients previously classified in amnestic single-domain (aMCI) and amnestic multidomain (mdMCI) subtypes; to test inter-rater reliability and to compare different subtypes of MCI, attempting to define performance profiles according to qualitative analyses of errors. Methods: The study includes two clinical groups: aMCI and mdMCI, each with 90 subjects, recruited at the Neurology Department of the Centro Hospitalar e Universitário de Coimbra. Their performance was compared with a cohort of 90 community-dwelling controls matched according to gender, age and education. All participants were assessed with Mini Mental State Examination, Montreal Cognitive Assessment (MoCA) and CDT. Clock drawings of MCI patients were scored by a neuropsychologist and an inexperienced rater using three scoring systems - Rouleau, Cahn and Babins. Data were analysed with the Statistical Package for the Social Sciences. Results: There was high inter-rater reliability in CDT scoring systems (p<0,001). Significant correlations were found between the cognitive screening instruments and CDT scoring systems as well as a consistent relationship with performance in visuospatial and executive domains of the MoCA. We also observed qualitative differences between both forms of DCL, with higher error rate of “Conceptual deficit” and “Perseveration” in mdMCI, and “Nonspecific spatial error” regarding the aMCI group. There was only sufficient (60%) discriminatory capacity of total scores of the CDT, comparing control and MCI subjects. Conclusions: Our study showed that CDT scoring systems have high inter-rater reliability to screen for MCI and can be applied in large scale studies and primary health care. Although in this context CDT revealed only sufficient discriminatory capacity and should be used with other cognitive screening tests in order to increase the diagnostic accuracy.