Outcomes of Mild Cognitive Impairment by Definition

Abstract

Mild cognitive impairment (MCI), the cognitive state intermediate between normal cognition and dementia, is interesting because of the potential for MCI to eventually develop into full-blown dementia. The original Mayo Clinic criteria for amnestic MCI¹ focused on deficits in and complaints about memory. The revised International Working Group (IWG) on Mild Cognitive Impairment criteria² expanded the concept to include objective and subjective impairments in any of several cognitive domains. The Clinical Dementia Rating (CDR)³ approach focuses on decline in cognitively driven everyday function rather than on objective cognitive deficits. Other approaches have used purely neuropsychological definitions of MCI based on objective deficits relative to norms.^4-7 Regardless of the definition used, individuals with MCI progress to dementia in higher proportions than do cognitively normal people; however, the actual proportions vary across definitions^4,5,8-10 and across operational versions of the same definitions.^11-13 Rates of progression from MCI to dementia are consistently lower in community settings than in specialty clinical and research programs where individuals with MCI seek services^11,12 despite using the same criteria.¹⁴ All population-based studies^4,8,10-12 find substantial proportions of individuals with variously defined MCI remaining stable or even reverting to normal during follow-up.