Reed Tanea T., Sultana Rukhsana, Butterfield D. Allan
Mild cognitive impairment (MCI) is generally referred to as the transitional zone between normal cognitive aging and early dementia or clinically probable Alzheimer’s disease (AD) (1), although not all AD patients pass through an MCI stage. The term was first coined by Petersen (2). Most individuals with MCI eventually develop AD, which suggests MCI may be the earliest phase of the AD (–6). MCI can be divided into two broad subtypes: amnestic (memory-affecting) MCI or non-amnestic MCI (2,7). Other functions, such as language, attention, and visuospatial skills, may be impaired in either type. Amnestic mild MCI patients characteristically have subtle but measurable memory disorder not associated with dementia. Individuals with MCI are at an increased risk of developing AD, or another form of dementia with a rate of progression between 10% and 15% per year (8,9), although there have been cases where patients have reverted to normal (1,10,11). Criteria for MCI include (a) a memory complaint corroborated by an informant; (b) objective memory test impairment (age and education adjusted); (c) general normal global intellectual function; (d) activities of daily living not disturbed; (e) clinical dementia rating (CDR) score of 0.0 to 0.5; (f) no dementia; and (g) a clinical evaluation that revealed no other cause for memory decline (12). Moreover, neuroim-aging studies by magnetic resonance imaging (MRI) demonstrate the atrophy of the hippocampus or entorhinal cortex in MCI patients, indicating the relationships with transition of normal aging to MCI, then later to clinical AD (13). Pathologically, MCI brain shows mild degradation of the hippocampus, entorhinal cortex, sulci, and gyri using MRI (14,15). These aforementioned areas undergo considerable degradation in AD (–20). Since the hippocampus is the region of the brain primarily responsible for processing memory, it is clearly understandable why those persons with AD and MCI have memory loss.
轻度认知障碍（MCI）通常被认为是正常认知衰老与早期痴呆或临床可能的阿尔茨海默病（AD）之间的过渡阶段（1），尽管并非所有AD患者都会经历MCI阶段。该术语最早由彼得森提出（2）。大多数MCI个体最终会发展为AD，这表明MCI可能是AD的最早阶段（-6）。MCI可分为两种主要亚型：遗忘型（影响记忆）MCI或非遗忘型MCI（2,7）。两种类型的患者在语言、注意力和视觉空间技能等其他功能方面可能都会受损。遗忘型轻度MCI患者的特征是存在细微但可测量的记忆障碍，且与痴呆无关。MCI个体患AD或其他形式痴呆的风险增加，每年的进展率在10%至15%之间（8,9），不过也有患者恢复正常的病例（1,10,11）。MCI的诊断标准包括：（a）有知情者证实的记忆主诉；（b）客观记忆测试受损（根据年龄和教育程度进行调整）；（c）整体智力功能基本正常；（d）日常生活活动未受干扰；（e）临床痴呆评定量表（CDR）评分为0.0至0.5；（f）无痴呆；（g）临床评估未发现其他导致记忆衰退的原因（12）。此外，通过磁共振成像（MRI）进行的神经影像学研究表明，MCI患者的海马体或内嗅皮质萎缩，这表明了从正常衰老到MCI，再到临床AD转变之间的关系（13）。在病理上，使用MRI观察到MCI大脑的海马体、内嗅皮质、脑沟和脑回有轻度退化（14,15）。在AD中，上述区域会发生相当程度的退化（-20）。由于海马体是大脑中主要负责处理记忆的区域，所以AD和MCI患者出现记忆丧失的原因也就显而易见了。
