Oculomotor abnormalities in posterior cortical atrophy: are they different from those in Alzheimer's disease after all?

摘要

Posterior cortical atrophy (PCA) is a progressive degenerative condition characterized by a gradual loss of visual skills and other posterior cortical functions due to atrophy of parietal, occipital and occipito-temporal brain regions (Lehmann et al., 2011). It is associated with a relative preservation of memory, language skills and judgement until late in the clinical course. Core features of PCA include partial or complete Balint's syndrome (simultanagnosia, optic ataxia and ocular apraxia) and Gerstmann's syndrome (acalculia, agraphia, finger agnosia), along with various combinations of visuo-spatial and visuo-perceptual impairments (Crutch et al., 2012), apparent despite an otherwise normal ophthalmo-logical examination. In this issue of Brain, Shakespeare et al. (2015) compare and contrast eye movement abnormalities revealed by basic oculomotor tests in patients with PCA, typical Alzheimer's disease and healthy controls, in order to determine the extent to which abnormalities in basic (lower-order) oculomotor function contribute to visuo-perceptual disturbances in PCA (Shakespeare et al., 2015). Patients with PCA typically present when they are between 50 and 65 years of age (Crutch et al., 2012). One of the most important manifestations of PCA is simultanagnosia, an inability to synthesize the overall meaning of a visual scene despite being able to identify its individual elements; this should be suspected when a patient presents with an inability to read pseudo-isochromatic plates, despite intact colour vision (Beh et al., 2015). The relative rarity of PCA makes it difficult to recruit large cohorts, but recently the number of studies of this disorder, often referred to as the cardinal visual dementia and the most common atypical Alzheimer's disease phenotype, has been increasing.