Neuropsychological measures predict decline to Alzheimer's dementia from mild cognitive impairment.

Abstract

Studies of Mild Cognitive Impairment (MCI) show elevated rates of conversion to dementia at the group level. However, previous studies of the trajectory of MCI identify great heterogeneity of outcomes, with a significant proportion of individuals with MCI remaining stable over time, changing MCI subtype classification, or reverting to a normal cognitive state at long-term follow-up. The present study examined individual outcomes at 20 months in a group of older adults classified according to MCI subtypes. A total of 106 participants, 81 with different subtypes of MCI and 25 healthy controls, undertook longitudinal neuropsychological assessment of visual and verbal memory, attentional processing, executive functions, working memory capacity, and semantic memory. At 20 months 12.3% of the MCI group progressed to dementia, 62.9% continued to meet MCI criteria, and 24.7% reverted to unimpaired levels of function. A discriminant function analysis predicted outcome at 20 months on the basis of baseline neuropsychological test performance with 86.3% accuracy. The analysis indicated that a pattern of impairments on visual episodic memory, verbal episodic memory, short-term memory, working memory, and attentional processing differentiated between participants who developed dementia, recovered from MCI, or remained in stable MCI. The results of the present study raise questions regarding the specificity of existing criteria for the subtypes of MCI, with these results indicating a high degree of instability in classification over time. In addition, the results suggest that multidomain MCI is the most reliable precursor stage to the development of AD.