Patterns of Atrophy Differ Among Specific Subtypes of Mild Cognitive Impairment

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Abstract
Mild cognitive impairment (MCI) is considered a transitional stage between normal aging and a diagnosis of clinically probable Alzheimer disease (AD). The original description of amnestic MCI (aMCI) noted but did not explicitly differentiate 2 variants, one in which only memory was impaired and a second in which impairments in nonmemory domains could be present but memory was the predominant domain impaired. The critical distinction between MCI and AD in subjects with predominant memory impairment plus less pronounced impairment in nonmemory domains was preservation of normal activities of daily living. At a consensus conference in Stockholm in 2003,1 the classification of MCI was expanded to formally recognize that, in patients with predominantly memory impairment, other nonmemory cognitive domains can be affected, including language, attention/executive, and visuospatial skills. It was also recognized that the various clinical subtypes of MCI should be defined on the basis of the specific cognitive domain affected.2,3 In this article, amnestic single-domain MCI (aMCI-SD) refers to the subtype in which memory is the only impairment; amnestic multiple-domain MCI (aMCI-MD), the subtype that demonstrates impairment in memory and at least 1 other neuropsychological domain; nonamnestic single-domain MCI (naMCI-SD), the subtype associated with impairment in 1 nonmemory domain; and nonamnestic multiple-domain MCI (naMCI-MD), the subtype associated with impairment in 2 or more nonmemory domains. This 4-group classification scheme proposed in 20031 has been adopted by the National Institute on Aging Alzheimer's Disease Centers Program for the Uniform Data Set. It is also being used to classify subjects for the Alzheimer's Disease Neuroimaging Initiative. Although this Initiative uses the 4-group scheme for MCI classification,4 only subjects with aMCI are enrolled in the study. In all previous imaging studies published from the Mayo Clinic, only subjects with aMCI were included in the study analysis. In the current study, however, we analyzed patterns of gray matter atrophy in subjects in all 4 possible MCI groups.