Homonymous Hemianopia in Posterior Cortical Atrophy: right-left Asymmetry, Progression over Time and Relationship to the Classical Neuropsychological Deficits

Abstract

Following Benson's seminal paper published in 1988 visual field loss in Posterior Cortical Atrophy (PCA) has been largely denied or ignored. This is despite an earlier description by Cogan of a similar case of pathologically verified Alzheimer disease featuring homonymous hemianopia (HH). Although HH is now recognised as a core feature of PCA its characteristics and relationship to other PCA features are unexplored. This study aimed to characterise the perimetric abnormalities in PCA patients presenting with HH, focusing on the response to static and kinetic stimuli; progression of the deficit over time; and the relationship to co-existing cognitive deficits. 24 patients were recruited for the cross-sectional study, of whom 19 participated in the longitudinal study. Each assessment consisted of kinetic and static perimetry and a comprehensive neuropsychological evaluation. The latter included tests to all basic cognitive domains plus tests of posterior cortical function. Thirteen patients underwent additional kinetic perimetry using three target velocities. Left HH was predominant and a deficit in object perception universal. Neglect was uncommon and did not correlate with the laterality of the HH. Stato-kinetic dissociation (SKD) was observed in all patients, greater in the more affected hemifield. Longitudinally, static perimetric deficits declined at a greater rate in the initially more affected hemifield. The rate of decline to kinetic testing was lower and varied with target size and velocity. Deterioration to the smallest and lowest velocity target mirrored that of static loss. A longitudinal mixed-model analysis showed that right HH was associated with greater deficits in predominantly left hemisphere cognitive functions and bilateral HH with greater bilateral occipital deficits. However, no association was found between the laterality of the HH and right hemisphere cognitive deficits. The characteristic SKD (also known as the Riddoch phenomenon) does not represent a complete dissociation as kinetic detection deteriorates over time in all cases. The correlation of the HH with lateralised parietal deficits challenges the concept that HH is restricted to an extreme posterior variant of PCA and highlights the need for routine (static and kinetic) perimetry in the diagnosis, characterisation and monitoring of PCA.