Mild cognitive impairment: a clinically useful but currently ill-defined concept?

The term mild cognitive impairment (MCI) has gained wide currency among clinicians, and particularly dementia researchers, to denote patients with memory deficits who do not yet fulfil the criteria for dementia, but are at high risk of conversion. MCI is therefore regarded as the prodromic or pre-dementia stage of Alzheimer's disease. The accurate categorization of these subjects has far-reaching implications, both for research in this field and for those individuals who fall within this diagnostic group. Despite a wealth of studies examining the neuropsychological, neuroimaging and biological profiles of this population, the characterization of MCI remains controversial. This brief overview discusses a number of the issues related to this topic and questions the currently accepted criteria.