Posterior cortical atrophy: evidence for discrete syndromes of early-onset Alzheimer's disease.

Background: Posterior cortical atrophy (PCA) may represent a discrete syndrome of Alzheimer's disease (AD) rather than amnestic AD with visual deficits.
Methods: We separated 30 patients with PCA based on ventral and dorsal visual symptoms using cluster analysis and analyzed the demographic, cognitive, and functional imaging features.
Results: This analysis revealed subgroups of 26 dorsal and 4 ventral patients. The ventral subgroup had greater confrontational naming impairment, and the dorsal subgroup had greater hypofunction in the parietal regions. The PCA cohort had memory retrieval rather than encoding deficits, and clinical follow-up showed relative isolation of dorsal and ventral visual manifestations.
Conclusion: These results support 2, mostly nonoverlapping syndromes in patients with PCA, with the commonest affecting the dorsal visual pathway; moreover, the memory retrieval difficulty in the patients with PCA was dissimilar to the amnestic pattern in typical AD. These results suggest that, in most cases, PCA syndromes are discrete clinical variants of AD.