Visual Dysfunction in Posterior Cortical Atrophy

Introduction A classification framework for posterior cortical atrophy (PCA) is proposed to improve the uniformity of definition of the syndrome in a variety of research settings. Methods Consensus statements about PCA were developed through a detailed literature review, the formation of an international multidisciplinary working party which convened on four occasions, and a Web-based quantitative survey regarding symptom frequency and the conceptualization of PCA. Results A three-level classification framework for PCA is described comprising both syndrome- and disease-level descriptions. Classification level 1 (PCA) defines the core clinical, cognitive, and neuroimaging features and exclusion criteria of the clinico-radiological syndrome. Classification level 2 (PCA-pure, PCA-plus) establishes whether, in addition to the core PCA syndrome, the core features of any other neurodegenerative syndromes are present. Classification level 3 (PCA attributable to AD [PCA-AD], Lewy body disease [PCA-LBD], corticobasal degeneration [PCA-CBD], prion disease [PCA-prion]) provides a more formal determination of the underlying cause of the PCA syndrome, based on available pathophysiological biomarker evidence. The issue of additional syndrome-level descriptors is discussed in relation to the challenges of defining stages of syndrome severity and characterizing phenotypic heterogeneity within the PCA spectrum. Discussion There was strong agreement regarding the definition of the core clinico-radiological syndrome, meaning that the current consensus statement should be regarded as a refinement, development, and extension of previous single-center PCA criteria rather than any wholesale alteration or redescription of the syndrome. The framework and terminology may facilitate the interpretation of research data across studies, be applicable across a broad range of research scenarios (e.g., behavioral interventions, pharmacological trials), and provide a foundation for future collaborative work.

Figures in which human observers perceive "illusory contours" were found to evoke responses in cells of area 18 in the visual cortex of alert monkeys. The cells responded as if the contours were formed by real lines or edges. Modifications that weakened the perception of contours also reduced the neuronal responses. In contrast, cells in area 17 were apparently unable to "see" these contours.

To determine the frequency of Alzheimer's disease (AD) pathology in patients presenting with progressive focal cortical syndromes, notably posterior cortical atrophy (PCA), corticobasal syndrome (CBS), behavioural variant frontotemporal dementia (bvFTD), progressive non-fluent aphasia (PNFA) (or a mixed aphasia) and semantic dementia (SD); and to compare the age of onset, evolution and prognosis in patients with focal cortical presentations of AD versus more typical AD and those with non AD pathology. From a total of 200 patients with comprehensive prospective clinical and pathological data we selected 120 : 100 consecutive cases with focal cortical syndromes and 20 with clinically typical AD. Clinical files were reviewed blind to pathological diagnosis. Of the 100 patients with focal syndromes, 34 had AD as the primary pathological diagnosis with the following distribution across clinical subtypes: all 7 of the PCA (100%); 6 of 12 with CBS (50%); 2 of 28 with bvFTD (7.1%); 12 of 26 with PNFA (44.1%); 5 of 7 with mixed aphasia (71.4%) and 2 of 20 with SD (10%). Of 20 with clinically typical AD, 19 had pathological AD. Age at both onset and death was greater in the atypical AD cases than those with non-AD pathology, although survival was equivalent. AD is a much commoner cause of focal cortical syndromes than previously recognised, particularly in PCA, PNFA and CBS, but rarely causes SD or bvFTD. The focal syndrome may remain pure for many years. Patients with atypical AD tend to be older than those with non-AD pathology.