Seeing why they cannot see: Understanding the syndrome and causes of posterior cortical atrophy

Abstract

Posterior cortical atrophy (PCA) is a syndrome defined by focal neurodegeneration of the parietal, occipital, and occipito‐temporal cortices and associated with progressive dysfunction of visual processing, praxis, numeracy and reading. The condition is most commonly caused by (and viewed as an atypical presentation of) Alzheimer's disease, although can also be caused by other degenerative diseases. The current paper examines the relationship of PCA to other degenerative syndromes, and considers what comparisons of these syndromes and disease phenotypes can tell us about underlying disease mechanisms. The focus then turns to neuropsychological investigations of the cognitive basis of symptoms which, although unusual in the broader context of a dementia clinic, are particularly characteristic of the PCA syndrome, before exploring implications for clinical management and patient and carer support.

Navigational cue effects in Alzheimer's disease and posterior cortical atrophy

“…However, there was an unexpected lack of evidence of a benefit of CCue + motion over CCue on primary and secondary outcomes, the only exception being weak evidence in the tAD group that the addition of motion patterns increased the number of trials where patients fixated on the target door. A greater benefit of CCue + motion had been anticipated following previous case reports of intact motion recognition in PCA . This study's findings may indicate that the frequency of the motion pattern was too low; while motion perception may be relatively preserved in tAD, this may only be at certain frequencies .…”

“…Previous studies suggest contrast‐ and color‐based cues assist bathroom‐finding and reduce wandering for people with dementia, although evidence is limited . Motion‐based cues are promising, given how aspects of visual motion detection may be relatively preserved in tAD and PCA . The current investigation intends to maximize the translational potential of findings through assessing cue effects across different patient phenotypes and environmental conditions within a controlled real‐world setting.…”

(Con)text-specific effects of visual dysfunction on reading in posterior cortical atrophy

“…The second perceptual attribute of particular interest in the current study is font size. Many PCA patients describe greater difficulty perceiving large than small objects (perhaps most strikingly by a patient who was unable to read the headlines of his newspaper but could read those of another passenger reading the same paper further down the train carriage on which he was travelling; see Crutch, 2013 ). Such ‘reverse size effects’ have been documented formally in a small number of patients with progressive visual disturbance who exhibited more impaired identification for large relative to small pictures, words and letters presented in isolation ( Coslett, Stark, Rajaram, & Saffran, 1995; Saffran, Fitzpatrick-DeSalme, & Coslett, 1990; Stark, Grafman, & Fertig, 1997 ).…”

Facilitating text reading in posterior cortical atrophy

“… 18 , 19 This motion was intended to act as a cue to assist disorientated readers, following reports of patients with PCA being able to better localize moving stimuli. 20 , 21 The double-word condition in addition presented the subsequent word in each passage to the right of the fixation box in order to assess whether participants' reading would benefit from the presence of words to the right of fixation. 22 , 23 Words remained stationary within the fixation box until read; subsequently, consecutive words were moved into the box by the experimenter ( figure 3A ).…”