Ophthalmological and cognitive data in t-AD and PCA

Alzheimer's disease (AD) manifests commonly as an amnestic syndrome (tAD), but also as a rarer focal type, such as Posterior Cortical Atrophy (PCA-AD), which primarily impairs visuospatial functions. In addition to the brain atrophy, retinal degeneration has been demonstrated, associated with the accumulation of Ab and Tau protein in this tissue, which shares a common origin with the brain. Additionally, retrograde trans-synaptic degeneration from the brain could affect the retina. We hypothesized that such dying-back phenomenon would be more important in PCA-AD than in tAD and that this would be reflected on specific optical coherence tomography (OCT) measures.Twenty-nine AD patients were categorized into 15 typical and 14 PCA forms. Complaints and symptoms were evaluated using a specific screening battery developed to detect PCA (Q-ACP questionnaire, neuropsychological parietal and non-parietal scales). Neuroimaging was performed to determine brain atrophy and its lateralization. OCT imaging allowed to measure the volumes of the macular ganglion cell layer (GCL) and of the retinal nerve fiber layer (RNFL) of the optic nerve.While the global RNFL thickness and GCL volume were not statistically different, PCA-AD patients showed more thinning than tAD in the inferior temporal (IT) sector on both eyes. Moreover, the amount of thinning in this sector was correlated with the score at the Q-ACP questionnaire and at the neuropsychological parietal scales.We propose that the thinning in the IT sector reflects the retrograde damage to the magnocellular pathway which constitutes a major feed of the dorsal visual stream primarily damaged in PCA. <br>

阿尔茨海默病（Alzheimer's disease, AD）通常表现为遗忘综合征（tAD），但也可表现为罕见的局灶亚型，如后部皮层萎缩型阿尔茨海默病（Posterior Cortical Atrophy, PCA-AD），该亚型主要损害患者的视空间功能。除脑萎缩外，已有研究证实视网膜变性与该组织内Ab蛋白与Tau蛋白的沉积相关，而视网膜与脑具有共同的发育起源。此外，脑内的逆行跨突触变性亦可累及视网膜。我们提出假说：这种溃变现象（dying-back phenomenon）在PCA-AD患者中较tAD患者更为显著，且可通过特定的光学相干断层扫描（optical coherence tomography, OCT）指标体现。本研究共纳入29例AD患者，分为15例典型遗忘型AD与14例PCA-AD亚型。采用专为筛查PCA开发的标准化评估组合（Q-ACP问卷、神经心理学顶叶量表与非顶叶量表）对患者的主诉与症状进行评估。通过神经影像学检查明确患者的脑萎缩情况及其偏侧化特征。利用OCT成像测量了视神经的黄斑神经节细胞层（macular ganglion cell layer, GCL）体积与视网膜神经纤维层（retinal nerve fiber layer, RNFL）体积。尽管全视网膜神经纤维层厚度与黄斑GCL体积在两组间未呈现统计学差异，但PCA-AD患者双眼颞下（inferior temporal, IT）象限的视网膜变薄程度均显著高于tAD患者。此外，该象限的视网膜变薄程度与Q-ACP问卷得分及神经心理学顶叶量表得分呈显著正相关。我们认为，颞下（IT）象限的视网膜变薄可反映大细胞通路的逆行性损伤——该通路是背侧视觉通路的主要输入来源，而背侧视觉通路正是PCA-AD患者的主要受损靶点。<br>