Vol 6 n° 4 - Mild Cognitive Impairment
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pidemiology involves the observation of health states within a general population context. In the case of mild cognitive impairment (MCI), this is important in that we are dealing with what is essentially a subclinical state, ie, a health problem that is likely to remain unre- ported to a health professional for an extended period of time, and for which the most common first point of con- tact will be the general practitioner. It is also a heteroge- neous entity: subclinical cognitive disorder has multiple interacting causes, as illustrated in Figure 1. While the concept of MCI has progressively been narrowed down to a subgroup of persons in the first stages of a probable neurodegenerative process, this group will nonetheless be  subject  to  many  of  the  other  causes  of  cognitive decline, which will interact with the disease process and complicate the definition and screening of MCI. General population studies of a disorder allow us to see the full range of cases within a naturalistic setting, which includes 4 0 1 C l i n i c a l   r e s e a r c h E Copyright © 2004 LLS SAS.  All rights reserved www.dialogues-cns.org Mild cognitive impairment: an epidemiological perspective Karen Ritchie, PhD Keywords:  cognition; relevance; incidence; risk; etiology Author affiliations: Institut National de la Santé et de la Recherche Médicale (INSERM), E361 Epidemiology of Nervous System Pathologies, La Colombière Hospital, Montpellier, France Address for correspondence:  Institut National de la Santé et de la Recherche Médicale (INSERM), E 361 Pathologies of the Nervous System: Epidemiological and Clinical Research, Hôpital La Colombière, 34093 Montpellier Cedex 5, France
(e-mail: ritchie@montp.inserm.fr) Mild cognitive impairment (MCI) refers to cognitive impairment that is assumed to be due to pathological central ner- vous system processes, but which interacts with normal aging-related changes. Epidemiological studies conducted in the general population have been able to examine more heterogeneous forms of this disorder than clinical studies, and have also been able to provide early estimations of population incidence and prevalence. Large differences in case identification procedures and sampling methods have led to considerable divergence in the rates of prevalence reported, which ranged from 1% to 29%. Suggested improvements in the definition of MCI have led to an upward adjustment of prevalence rates in most studies, giving between 5% and 29%. Incidence is estimated as 8 to 58 new cases per thousand persons per year, and the probability of conversion from MCI to dementia is estimated at around 15%. The principal risk factors that have been identified so far for MCI using regression models applied to general population data are age, education, race, medicated hypertension, infarcts, white matter lesions, depression, and apolipoprotein E4 (APOE-4) allele. An etiological model derived from these studies indicates possible intervention points for future therapeutic strategies at the level of both clinical intervention and environmental exposure. There is, however, a clear need for epidemiological studies that take into account a broader range of risk factors than those studied to date, which have focused principally on known risk factors for dementia.   © 2004, LLS SAS Dialogues Clin Neurosci. 2004;6:401-408.