To assess the utility of the Mini Mental State Exam (MMSE) and Montreal Cognitive Assessment (MoCA) for tracking cognitive changes Huntington’s Disease.

Currently, the most frequently used brief assessment of global cognitive functioning is the MMSE. Although the MMSE is helpful for distinguishing individuals without significant cognitive impairment from those with dementia, it is not particularly sensitive to more subtle cognitive deficits. The MoCA is another brief cognitive screening tool that has been shown to be more sensitive to mild impairment and may have greater usefulness in subcortical dementias because of its more extensive assessment of executive function. Although the MoCA appears to have high sensitivity and specificity in a variety of neurological populations, there is currently little known about its efficacy in tracking cognitive decline in individuals with HD. We used a mixed effects model to analyze MMSE and MoCA scores collected prospectively during 5 years of follow-up for 163 patients with HD seen at one academic HDSA Center of Excellence. Baseline mean age for the HD cohort was 51.35 years, mean education 14.46 years, and a mean CAG repeat length 43.95. Mean follow-up time was 3.33 years.

Mean MMSE and MoCA scores at baseline were 25.13 (SD=1.66) and 22.76 (SD=3.70) respectively. At baseline, age and gender were not associated with MMSE and MoCA scores, while years of education were. Neither age nor gender predicted rate of decline for the MoCA while years of education predicted rate of decline for the MMSE. For the MMSE, each year of education predicted on average 0.51 points higher score at enrollment; for the MoCA, each year of education predicted on average 0.79 points higher score at enrollment. The mean rates of decline on the MMSE was 0.48 points per year (p<.001) while that on the MoCA was only 0.31 points annually (p<.001) in the first five years of observation.

The MMSE and MoCA decline significantly over time in an unselected HD population. The smaller rate of decline in the MoCA may be due, in part, to the greater variability in baseline, MoCA (SD=3.70) vs MMSE (SD=1.66) scores in our HD cohort. Unlike cortical dementias, such as Alzheimer’s disease (AD), where declines of 2-3 points per year have been described for the MMSE and MoCA, much lower annual rates of decline have been reported in subcortical dementias such as Parkinson’s disease. To our knowledge, this is the first report of rate of cognitive decline on the MMSE and MoCA in HD: such information is vital for adequately preparing patients and families for future needs, in addition to planning for interventional/treatment trials in HD.