Unmasking the heterogeneity of Alzheimer's disease: case studies of individuals from distinct neuropsychological subgroups.

Case descriptions of patients with probable Alzheimer's disease (AD) who were reliably classified into three neuropsychological subgroups (global [GAD], right-hemisphere [RAD], and left-hemisphere [LAD]) in an earlier cluster analytic study (Fisher et al., 1996) are presented. Concordance between the neuropsychological patterns and clinical histories of randomly selected and hand-selected cases from within each subgroup was high. Longitudinal analysis revealed stable subgroup-specific neuropsychological progression patterns. Results are discussed in terms of future research avenues worth pursuing, in addition to the conceptual shift in research design necessary to uncover both quantitative and qualitative subgroup-specific ability differences.