False recognition helps to distinguish patients with Alzheimer's disease and amnestic MCI from patients with other kinds of dementia.

Two recent reviews on neuropsychological assessment argue that Alzheimer's disease (AD) is characterized by deficits in delayed recall and that this allows differentiating AD from other types of dementia. We attempted to differentiate patients with AD and amnestic mild cognitive impairment (MCI) from patients with fronto-subcortical dementia, normal pressure hydrocephalus and vascular dementia using a simple picture recognition task. We examined 130 patients, 89 with dementia and 41 with MCI. The combination of the CERAD-NP savings score and the number of false recognitions yielded a sensitivity of 100% for identifying AD patients. Moreover, adding the score for false recognitions to that of delayed recall improved the specificity of the diagnosis from 50% to 90%. After matching the groups on memory performance, the AD group still produced more false recognitions. The results suggest that delayed recall impairment and recognition errors stem from different sources. We also found that the number of false recognitions differs between amnestic and non-amnestic MCI patients. The quality of the differential diagnosis may therefore be enhanced significantly by taking into account both delayed recall and false recognitions provoked by a picture recognition task.