Assessing mild cognitive impairment among older African Americans.

Researchers have focused on identifying the transitional period of normal cognition and dementia. Several terms have been used to describe this period, but the term Mild Cognitive Impairment (MCI) has often be used in the literature (Albert, 2008). Depending on the diagnostic guidelines used to measure MCI, the prevalence rates of MCI range from 3% to 53.8% (Panza, D’Introno, Colacicco, Capurso, Del Parigi, Caselli et al., 2005). Although previous research of racially mixed samples has suggested that African Americans are at a greater risk for the development of MCI than Caucasians (Manly, Tang, Schupf, Stern, Vonsattel, and Mayeux, 2008), there is still limited research exploring MCI among older African Americans. The purpose of this investigation was to examine the frequency of MCI among a sample of older African Americans and the specific cognitive domains of impairment for individuals meeting the criteria for MCI. The prevalence of dementia in older African Americans has shown to be significantly higher than in older Caucasians at baseline testing (33.7% vs. 20%) and at a one year follow-up (32.1% vs. 18.9%; Gurland et al., 1999). The incidence of dementia, specifically Alzheimer’s disease, is almost double among African Americans compared to Caucasians (Tang, Cross, Andrews, Jacobs, Small, Bell et al., 2001). Even though African Americans are disproportionately affected by dementia, this has not led to many studies on MCI in this understudied population. This is surprising, considering racial differences have been observed in clinical and genetic etiologies of dementia (Farrer, Cupples, Haines, Hyman, Kukull, Mayeux et al., 1997; Fillenbaum, Prosnitz, Raiford, Burchett, and Clark, 1991; Froehlich, Bogardus, and Inouye, 2001;). In fact, certain clinical types of dementia, such as vascular or multi-infarct dementia, are more common in African Americans than Caucasians (de la Monte, Hutchins, and Moore, 1989; Heyman et al., 1991). In contrast, the presence of apolipoprotein E(APOE)-e 4 allele is less of genetic risk for Alzheimer’s disease in African Americans than Caucasians (Farrer et al., 1997; Tang, Maestre, Tsai, Liu, Feng, Chung et al., 1996). Thus, specific cognitive domains of initial impairment among this population may differ from what previous studies of predominately Caucasian samples have reported, and there might be a unique onset and course of MCI among African Americans. Culturally relevant factors such as disparities in health could explain cognitive functioning within African Americans (Whitfield, Allaire, Belue, and Edwards, 2008). For example, the prevalence of cardiovascular disease is highly prevalent among African Americans (Cooper, Cutler, Desvigne-Nickens, Fortmann, Friedman, Havlik et al., 2000; Whitfield, Weidner, Clark, and Anderson, 2002), and cardiovascular disease or increased cardiovascular risk factors are associated with impairments in cognitive domains other than memory (Lezak, Howieson, and Loring, 2004), such as executive function and speed (Knopman, Boland, Mosely, Howard, Liao, Szklo et al., 2001). Research indicates that cognitively normal individuals with cardiovascular disease are at an increased risk for developing MCI (Tervo, Kivipelto, Hanninen, Vanhanen, Hallikainen, Mannermaa et al., 2004)and, subsequently, vascular dementia, which is highly prevalent among African Americans (Froehlich et al., 2001). Given this, early cognitive impairments may be observed in non-memory tasks and several health as well as demographic factors may explain these impairments, particularly among African Americans. The purpose of this investigation was to examine the frequency of MCI among African Americans and the specific cognitive domains of impairment for individuals meeting the criteria for MCI. The current study was guided by three specific aims. The first aim was to investigate the frequency of MCI in our sample. The second aim was to examine within the MCI group the number and types of cognitive domains in which individuals showed impairment. Finally, the third aim was to examine whether there are significant differences between MCI and cognitively normal individuals in demographic characteristics, health factors, and cognitive performance.