Characterization and Differences Between Possible and Probable Mild Cognitive Impairment in an Alzheimer’s Disease Center

BACKGROUND: Mild cognitive impairment (MCI) is considered an intermediate state between normal aging and dementia. A subjective cognitive complaint (SCC) is a key component in the diagnosis of MCI. However, some individuals with SCCs do not show objective impairment on neuropsychological measures and there has been debate about the role of SCCs for the characterization of MCI. This study aimed to examine the differences in neurocognitive function and other risk factors between MCI subtypes and better understand the role of the SCC when objective cognitive impairment is not present. SUBJECTS: This retrospective study includes 395 participants [age (M, SD) =67.5(7.2), education (M, SD)=15.10(2.7)], from the Alzheimer’s Disease Center (ADC) at the University of Texas Southwestern Medical Center who were English speaking and between the ages of 50-90. Participants received a comprehensive clinical assessment including neuropsychological testing and diagnosis, which was made via multidisciplinary group consensus. This study consisted of participants classified at their baseline ADC visit as individuals with SCC but normal cognitive performance (possible MCI, n=83), individuals with SCC and abnormal cognitive performance (probable MCI, n=121), and normal controls (n=191). METHOD: Differences in performance on neuropsychological measures among possible MCI, probable MCI, and normal control groups were examined using MANOVA. Differences in the frequency of selected cognitive and vascular risk factors, including APOE4, hypertension, high cholesterol, and diabetes mellitus, were examined using chi square test of independence. Demographic differences (age, education, gender, depression, and premorbid intelligence) across groups were compared using either ANOVA or chi square. RESULTS: Normal controls performed significantly better than the probable MCI group on the MMSE, TMT-A, TMT-B, Block Design, WCST, FAS, Animal Fluency, and BNT (p<.05). On the CVLT, normal controls demonstrated fewer intrusion errors, higher total learning scores, and better long delay free recall than both the possible and probable MCI groups, and similarly, the possible MCI group performed significantly better than the probable MCI group. The frequency of APOE4 did not differ significantly among groups (p>.05). The probable MCI and possible MCI group had significantly higher rates of hypertension (58%, 59%) compared to the normal control group (46%). The probable MCI group had significantly higher rates of high cholesterol (66%) than the possible MCI group (18%). The probable MCI group had significantly more males, lower education, and higher GDS scores compared to NC groups (p<.05). DISCUSSION: This study demonstrated that the probable MCI group differed from normal controls on measures of memory, executive function, and language, and had higher rates of hypertension and high cholesterol. Although statistically significant differences among all three groups on measures other than complex verbal memory were not seen; closer examination of the neurocognitive test scores showed that the possible MCI group performances were qualitatively more similar to that of the probable MCI group rather than the NC group. This may support the notion that individuals with a SCC but without overt impairment on testing do share commonalities with those with clear MCI, indicating that SCC do carry clinical significance and warrant evaluation and monitoring over time in older individuals.