Evolution of cognitive deficits and conversion to dementia in patients with mild cognitive impairment: a very-long-term follow-up study.

Ten patients with mild cognitive impairment (MCI) underwent extensive neuropsychological evaluation at 12-monthly intervals for a minimum of 6 years. All 10 patients declined and 5 have now died. The onset of dementia, as defined by a fall in global cognitive function (MMSE <24) or activities of daily living (Clinical Dementia Rating Scale; CDR) ranged from 1 to 8 years with generally good concordance between these measures. The rate of decline on the MMSE was highly variable ranging from 0.86 to 2.83 points per year. Other than a consistent impairment on tests of episodic memory and category fluency (8 out of 10), other early cognitive deficits were difficult to define and tended to be unstable in the early stages. Impairment of semantic memory, visuo-spatial and attentional abilities eventually developed but the sequence of deficit acquisition was heterogeneous. These findings are discussed in the light of current views of MCI. Amnestic MCI may not be an accurate concept unless semantic memory impairment is also considered as an integral core deficit. Full-blown dementia may take many years to develop in patients with MCI but was a universal feature in this study.