[Concept and clinical presentation of mild cognitive impairment]

Mild cognitive impairment (MCI) is considered to be a transition state between normal cognition and dementia. The subtype of MCI are highly heterogeneous in terms of etiology, presentation, and prognosis. Patients with the amnestic subtype of MCI are at a high risk of progression to Alzheimer disease (AD); this subtype may represent the prodromal stage of AD. In contrast, patients with the non-amnestic subtype may be at a high risk of progression to a non-AD dementia, including dementia with Lewy bodies, frontotemporal dementia, and vascular dementia. Most patients with amnestic MCI exhibit pathologic abnormalities in the mesial temporal lobe structures; several other concomitant pathologic abnormalities, including argyrophilic grain disease, neurofibrillary tangles, hippocampal sclerosis, and vascular lesions are also observed. Patients with MCI often exhibit neuropsychiatric symptoms, such as depression and apathy, and instrumental ADL are minimally restricted. Moreover, patients with MCI who are not aware of their memory deficits and in whom practice effects are not observed exhibit parietotemporal hypoperfusion on single photon emission CT, indicating that these findings are predictors of progression to AD. In this review, I have discussed the most current aspects related to the concept and clinical presentation of MCI, with emphasis possible risk factors for conversion to dementia.