People are living longer and along with this phenomenon emerges the concern about the quality of life as the person ages. While dementia is by no means a natural consequence of aging, both its incidence and prevalence increase dramatically with age, from 0.5 percent per year at the age of 65 years to nearly 8%/year after the age of 85 years (Evans et al. 1989). Alzheimer's disease (AD) is the most common cause of dementia. Although the goals of treatment in patients with AD have been to improve or, at least, to slow the deterioration of memory and cognition and to maintain independent function, research is moving from controlling symptoms to early identification and prevention of age-related cognitive disabilities.

Increasing evidence now suggests that the early pathogenic process of AD is protracted and may extend over decades. This preclinical stage includes a latent phase stretching from years to decades, where there may be no observable symptoms of the disease, followed by a shorter prodromal phase where mild symptoms are observed but preclude a clinical diagnosis. Unknown promoting factors somehow associated with aging convert this latent phase into a malignant cascade of molecular events that lead to degenerative neuronal process (Katzman, 1993, Petersen et al. 1999). This intermediate or transitional stage has been referred to by various names including, incipient dementia, prodormal AD, isolated memory impairment, and mild cognitive impairment (MCI). Currently, MCI refers to the clinical condition between normal aging and AD in which people experience memory loss to a greater extent than one would expect for their age, yet they do not meet currently accepted criteria for clinically probable AD (Petersen et al. 1999). These people progress to clinically probable AD at a considerably accelerated rate compared with healthy age-matched individuals. Consequently, this condition has been recognized as suitable for possible therapeutic intervention. As Selkoe (1997) points out, the most effective treatments for complex, chronic diseases like AD are usually those that interrupt an obligatory step occurring before a progressive cascade of cell damaging events. Therefore, the earlier the detection the better possibilities of modifying the course of the disease.

This volume is a broad and encompassing resource that provides research findings on the transitional condition between normal aging and very early AD, consisting of 12 chapters written by acknowledged experts currently engaged as active researchers in their respective topic areas. The chapters are stellar in their readability and informative nature. The initial chapter written by the editor, Ronald Petersen, outlines the conceptual nature of MCI as it currently exists. It addresses some of the controversial areas, including its clinical presentation (amnestic form, multiple-domain form, and single non-memory domain) and the etiological heterogeneity, seen in degenerative as well as non-AD degenerative conditions such as hippocampal sclerosis. This last one may progress to other forms of dementia such as vascular dementia, or may remain static, thus forming a group of false-positive: patients with MCI who do not progress.

The clinical chapters (2, 3, and 11) provide an historical perspective of the cognitive and functional characteristics (chapter 2) and of the noncognitive symptoms, such as changes in mood, personality and emotion as potential early markers of the presence of AD (chapter 3). Chapter 11 reviews the different types of examination necessary for making the diagnosis of MCI including clinical history, mental status examination, general neurologic and medical exam, and neuropsychological testing. The role of neuropsychological testing in establishing the diagnosis of MCI has been controversial. Some have advocated strict cognitive cut-offs to operationalize the diagnosis, while others have proposed less rigorous clinical criteria. The neuropsychology chapters (4 and 5) raise questions as to the appropriate standards for comparison, and present normative and clinical approaches to the cognitive characterization of normal subjects.

The structural and functional aspects of neuroimaging of individuals with MCI are treated in chapters 6 and 7. Chapter 6 points out that MRI-based volumetric measurements of hippocampus and/or entorhinal cortex are useful predictors of progression from MCI to AD. Functional neuroimaging studies, using single photon emission computed tomography, have reported areas of hypometabolism in posterior cingulate, and using positron emission computed tomography individuals with a genetic (familial) risk factor of AD show areas of hypometabolism in the temporal parietal regions while they are still asymptomatic. Chapters 8 and 9 review the neuropathology of AD and MCI. Data suggest that normal aging is distinct from the neuropathology of MCI or of AD, but that the latter two are remarkably similar in type and neuroanatomical distribution of lesions and are primarily differentiated by the quantity of lesions. Biomarkers such as CSF tau, CSF AB42, and APP isoforms in platelets, neural thread protein, and p97 are discussed as important adjuncts in making the clinical diagnosis of MCI. The final chapter reviews the current status of AD therapy and outlines trials that are underway for MCI.

In conclusion, this book is a collection of well-written reviews that offers the most recent advancements in the field. Its chapters are well written, well organized, and well referenced. This integrated information can help to clarify whether MCI is truly a diagnostic entity that can be characterized for treatment intervention. Thus the concept of MCI could be a very useful classification for increasing the opportunity of effective treatment. It is important to keep in mind that MCI appears to identify persons at significantly elevated risk to progress to an untreatable dementia but there is still a large proportion of subjects that fulfill the MCI criteria who do not progress to dementia, therefore, the book should have included recommendation concerning ethical issues in the diagnosis and treatment of individuals with MCI.