In an earlier book “See but not seen”, there is a passage that shows that the world is not the same as it was in the mind when the mirror suddenly becomes unfamiliar to the self. This book describes a medical image from a popular science perspective: visual agnosia, a loss of contact between visually perceived objects and previously remembered material and becoming unrecognizable, is an acquired cognitive disorder caused by localized damage to the brain. In the past, we used to talk about this problem in stroke or tumor patients, but in fact, in a subtype of Alzheimer’s disease, posterior cortical atrophy, visual symptoms can be the only early manifestation.
Let’s look at a specific example: a 62-year-old female patient presented to the clinic complaining of a persistent loss of vision and spatial awareness for four years. Initially, she noticed that she could not distinguish directions when driving at night and always cut off when parking; the right side of her body often hit the door when walking. He sometimes could not find things at home when they were right in front of him. The patient usually loves to read, but over the past few years, he found that he could not concentrate on reading and often serially. When watching television, it seemed as if the images on the screen were slowing down. The patient first went to an ophthalmology examination and was referred to neurology after ophthalmology was ruled out. The patient’s initial cognitive function screen, the Brief Mental State Inventory, had a score of 26, which was basically in the normal range. However, the patient performed very poorly on one of the copying graphs (see Figure 1). A detailed neuropsychological assessment revealed severe impairment in visual-related tests such as drawing, reading, and naming, while other cognitive functions such as language, memory, attention, and executive functions were normal. Subsequent brain magnetic resonance imaging revealed significant brain atrophy in the posterior cerebral cortex, mainly in the parietal and occipital regions, and a clinical diagnosis of posterior cortical atrophy (PCA) was considered.
PCA is a class of neurodegenerative syndromes, which prominently manifests as visual-spatial impairment (poor orientation, disorientation, afraid to go out at night, etc.), diminished visual perception (difficulty seeing, no concept of spatial distance), and normal ophthalmological examination. In the same period, higher cortical dysfunction such as loss of reading, writing, recognition, and use may occur. The lesions mainly involve the parietal, occipital, and occipitotemporal cortices, and limited atrophy in the corresponding areas is seen on CT or MRI images, and PET or SPECT imaging reveals reduced blood flow in the corresponding areas. Because of the relative rarity and the fact that many patients are first diagnosed in ophthalmology rather than neurology, there is a certain amount of missed misdiagnosis. It was not until 1988 when it was systematically described by Benson, a Western scholar, that it received attention, and it has only been around 20 years since then, much shorter than Parkinson’s disease and Alzheimer’s disease (AD), which have a history of more than 100 years.
In terms of pathological features, 80% of PCA patients show beta amyloid deposition and neuronal fiber tangles, which is consistent with Alzheimer’s disease and can be considered as a subtype of AD, also known as the visual variant of AD. The treatment can refer to AD by choosing drugs such as cholinesterase inhibitors. In addition, another 20% of PCA may have a pathological basis in less common diseases such as corticobasal ganglion degeneration and Lewy body dementia. Unlike typical AD, patients with early stage PCA usually have intact situational memory, normal language, attention and executive functions, self-awareness of the disease and a strong desire for treatment.