QUALITATIVE COMPARISON OF SEMANTIC MEMORY DEFICIT IN AMNESTIC MILD COGNITIVE IMPAIRMENT PATIENTS BASED ON AMYLOID STATUS

Semantic memory deficit is encountered in the clinic as commonly as episodic memory loss. However, due to its stability and gradualness in declining process, it is difficult to recognize semantic dysfunction in the early stage of disease. Therefore, it is necessary to evaluate qualitative aspects of semantic function including patterns of deficits as well as quantitative aspects of performance. In this study, we assessed the pattern of semantic memory deficits, especially focusing on lexical semantic memory, in patients with amnestic MCI (aMCI) who have a high probability of progressing into Alzheimer's dementia (AD). We hypothesized that β-amyloid (Aβ) positive aMCI may show semantic memory deficits qualitatively reminiscent of AD than Aβ(-) aMCI. From February 2015 to August 2016, patients who visited the Memory Clinic of Asan Medical Center underwent structural brain MRI, detailed neuropsychological test and [18F]-Florbetaben amyloid PET. Qualitative analysis of Korean-Boston naming test (K-BNT) and verbal fluency tasks including was conducted. A total of 217 participants were classified into four groups based on a visual scoring of amyloid PET scan and neurocognitive status: Aβ(-) normal cognition (normal control, n=53), Aβ(-) aMCI (n=66), Aβ(+) aMCI (n=56) and Aβ(+) AD(disease control, n=42). The frequency of the APOEε4 allele was significantly greater in Aβ(+) aMCI (53.5%) than Aβ(-) aMCI (22.2%)(p=0.002) and similar to that of AD (p=0.585). Other demographic factors did not show significant difference between the two aMCI groups. Global scale scores were not different between the two groups either. In terms of confrontational naming errors, Aβ(+) aMCI was more similar to AD than Aβ(-) aMCI, although there was no significant difference in the total K-BNT performance. Semantically related errors showed a decreasing proportion in the order of NC, Aβ(-) aMCI, Aβ(+) aMCI and AD, while semantically unrelated errors and visuo-perceptual errors showed an inverse pattern. This study suggests that dysfunction of semantic memory in the Aβ(+) aMCI are more similar to AD compared to Aβ(-) aMCI qualitatively. Early detection of semantic memory deficit similar to that of AD may be able to provide opportunities for early intervention using innovative cognitive training programs strengthening semantic system in the brain.