Evaluating the performance of the Montreal Cognitive Assessment in early stage Parkinson's disease

Mild cognitive impairment is common in Parkinson's disease, even in the early stages, and can be a risk for developing dementia. To properly track development and progression of cognitive impairment, reliable measurement tools are necessary. The Montreal Cognitive Assessment is currently used as a global cognitive screening tool and has been recommended as an abbreviated diagnostic tool to measure mild cognitive impairment in the context of global cognitive function. However psychometric properties of the Montreal Cognitive Assessment in PD have not been assessed in this context.

Data were obtained from the Parkinson's Progression Markers Initiative (n = 395). We examine psychometric properties of the Montreal Cognitive Assessment among newly diagnosed Parkinson's disease patients using Rasch analysis.

Only one item misfit the measurement model and principle component analysis indicated the Montreal Cognitive Assessment was unidimensional. Distribution of items calibrations formed a logical hierarchy from least to most challenging. Test items were markedly off-target (i.e., too easy) for this sample; this was also reflected in low person separation reliability. While 37% of participants performed all items correctly indicating a large ceiling effect, 22% of participants obtained a raw score in the range of 21-25 indicating mild cognitive impairment. No meaningful differential item functioning was detected.

Results suggest that in the context of early stage Parkinson's disease, the Montreal Cognitive Assessment is a unidimensional measure of global cognitive function. Implications for the use of the Montreal Cognitive Assessment in early stage Parkinson's disease and potential improvements to the assessment are discussed.