Mild Cognitive Impairment: International Perspectives. Holly A. Tuokko and David F. Hultsch (Eds.). 2006. New York: Taylor & Francis, 319 pp., $99.00 (HB).

As neuropsychologists, it is our job to differentiate normal from abnormal. We act as arbiters of behavior, defining “impairments” and using normative data and estimates of premorbid functioning to delineate post-injury or post-disease decline. Although one is obviously inclined to steer the diagnostic process in such a way as to comply with the prevailing taxonomy, because of the categorical nature of our classification system, this task is most difficult at the border zones, those areas that lie somewhere between “normal” and “abnormal.” The categories applicable to “abnormal ageing” have varied greatly over the years and are still evolving. Mild cognitive impairment or MCI is one such border zone category, which is believed to be a precursor to dementia in some patients. As with most border zone diagnostic entities, those patients at the cusp of the border will always be most difficult to classify. There will be certain low functioning “normal” people who score marginally low on our tests. Likewise, there will be certain high functioning “abnormal” people who score similarly. Even when the line is drawn with confidence and the MCI diagnosis is rendered, what does one impart to the patient about prognosis given the lack of clear relationship between the diagnosis and conversion to dementia, as well as the lack of clear relationship between the diagnosis and underlying brain pathology? It is a difficult and uncomfortable label because we know that a certain percentage we assign this moniker will “get better” (or is it regression to the mean?), become demented (or do they have less cognitive reserve?), or stay the same (or do they have more cognitive reserve?). The research literature behind abnormal ageing is incredibly diverse with regard to populations studied, methods of assessment, cut-offs utilized, nature and number of cognitive domains considered, and the extent to which subjective patient complaints are considered. As the heterogeneity in this construct becomes more apparent, there is need to increase the number of available labels as evidenced by evolving concepts like “amnestic MCI.” Thus, from a historical and clinical perspective, applying the term “MCI” is a bit like throwing a rock at a moving target.