Traykov L, Rigaud A-S, Cesaro P, Boller F
CHU Henri-Mondor, Université Paris XII, 51, avenue du Maréchal de Tassigny, 94010 Créteil.
Encephale. 2007 May-Jun;33(3 Pt 1):310-6. doi: 10.1016/s0013-7006(07)92044-8.
This analysis is centered on the study of cognitive disorders in Alzheimer's disease (AD), mainly for major neuro-psychological functions. We insist on the heterogeneity of the clinical picture peculiarly in the early stages of the illness, even if the deficits of episodic memory and of attentional/executive capacities are the first to deteriorate, preceding impairment in perceptual and language function and potentially having a substantial impact on the patient's capacity to cope independently. An episodic memory deficit is the hallmark of AD, but it must be stressed that this deficit may take different forms and its origin may be traced back to different cognitive mechanisms. One of the most striking aspects of episodic memory impairment in AD is the rapidity of forgetfulness on which screening and diagnostic tests of AD are based. There is some evidence that the episodic memory deficit in AD is one of learning (encoding and storage) of information rather than to a deficit of retrieval. Furthermore, episodic memory performance in AD depends on the integrity of semantic memory abilities, so giving support to a hierarchical model of organization of human memory. Finally, recent results show that an impairment of conscious recollection is responsible for the poor performance of AD patients in recognition memory. Executive deficits appear predominantly in tasks requiring cognitive flexibility and self-monitoring. With the progression of the disease, additional deficits are observed in the verbal concept formation abilities. These findings might be also very useful in the differential diagnosis between AD and the other cortical and subcortical dementias, as well as in the differentiation between AD and fronto-temporal dementia. We consider that studying early stages of the illness is necessary to delineate the diagnostic signs, to validate the new therapeutic experiments, to predict stages of decline. Recent research suggested that onset of AD is commonly preceded by an interim phase known as mild cognitive impairment (MCI). MCI refers to the clinical condition in which persons experience memory loss to a greater extent than one would expect for age, yet they do not meet currently accepted criteria for clinically probable AD. Persons who experience this condition are at increased risk for the development of AD. In MCI, despite the comparable global cognitive functioning, the findings show more impaired retrieval from long-term storage than in NC. The cued recall improves slightly the total recall but the recognition is significantly impaired. Moreover, the data indicate that MCI patients had additional problems with response inhibition, switching and cognitive flexibility. This suggests, that MCI may be identified by using a more detailed procedure for the assessment of cognitive decline than the evaluation of memory alone. As preventive strategies are developed and new cognitive enhancing therapies emerge, these results may also help us to define which domains are expected to improve in MCI populations.
本分析聚焦于阿尔茨海默病（AD）认知障碍的研究，主要针对主要的神经心理功能。我们强调临床表现的异质性，尤其是在疾病早期，即便情景记忆以及注意力/执行能力的缺陷最先恶化，早于感知和语言功能的损害，并且可能对患者的独立应对能力产生重大影响。情景记忆缺陷是AD的标志，但必须强调的是，这种缺陷可能有不同形式，其根源可追溯到不同的认知机制。AD情景记忆损害最显著的方面之一是遗忘的迅速性，而这正是AD筛查和诊断测试所依据的。有证据表明，AD中的情景记忆缺陷是信息学习（编码和存储）方面的缺陷，而非检索缺陷。此外，AD中的情景记忆表现取决于语义记忆能力的完整性，从而支持了人类记忆组织的层次模型。最后，近期结果表明，意识回忆受损是AD患者在再认记忆中表现不佳的原因。执行功能缺陷主要出现在需要认知灵活性和自我监控的任务中。随着疾病进展，在言语概念形成能力方面会出现更多缺陷。这些发现对于AD与其他皮质性和皮质下痴呆的鉴别诊断，以及AD与额颞叶痴呆的区分也可能非常有用。我们认为，研究疾病早期对于明确诊断体征、验证新的治疗实验以及预测衰退阶段是必要的。近期研究表明，AD发病前通常会有一个被称为轻度认知障碍（MCI）的中间阶段。MCI指的是这样一种临床状况，即人们经历的记忆丧失程度超过了根据年龄所预期的程度，但他们不符合目前临床上可能患有AD的公认标准。经历这种状况的人患AD的风险增加。在MCI中，尽管整体认知功能相当，但研究结果显示，与正常对照组相比，从长期存储中检索信息的能力受损更严重。线索回忆略微改善了总回忆，但再认显著受损。此外，数据表明MCI患者在反应抑制、转换和认知灵活性方面还有其他问题。这表明，可能需要使用比单纯评估记忆更详细的程序来评估认知衰退，以此来识别MCI。随着预防策略的制定和新的认知增强疗法的出现，这些结果也可能帮助我们确定MCI人群中哪些领域有望得到改善。
