Origins, controversies and recent developments of the MCI construct.

The MCI construct aims to investigate the grey area existing between normal aging and dementia, in order to identify it in the preclinical stage patients at risk of developing dementia. The construct of the MCI has been proposed by taking the neuropathological staging of the Alzheimer's disease (AD) as reference and providing an explicit set of identifying criteria, but it has raised two main problems: (a) the variability of estimates concerning the actual rate of conversion from MCI to dementia, and (b) the number of subjects who return to normality. These problems stem in part from the operational difficulties met by the MCI identifying criteria concerned with: the memory tests used, the cut-off adopted to identify patients with an 'objective' memory disorder, the assessment of subjective memory disorders, and the integrity of daily living activities. After a short discussion of these operational difficulties, I will pass to shortly survey the laboratory data providing additional predictive value for the conversion of MCI to dementia (ApoE4, CSF biomarkers, Neuroimaging data, and Vascular risk factors) and some recent attempts to identify pre-MCI patients, with a purely subjective cognitive impairment. I will conclude my review by asking if we have a single MCI or a family of MCI constructs, each of whom could play a preferential role in specific clinical contexts.