Olfactory detection and identification performance are dissociated in early Alzheimer's disease

Ten carefully screened men with very mild symptoms of Alzheimer's disease (AD) and ten healthy controls of similar age were compared on multiple chemosensory tasks: odor detection and identification, and taste detection. The patients scored significantly worse than controls on identification of odors and of a subset of airborne stimuli providing trigeminal stimulation. In contrast, the patients' olfactory detection thresholds as well as taste detection thresholds were not impaired relative to those of controls. The patients' scores on neuropsychological tests and the results 18F-2 deoxy-D-glucose PET studies did not correlate with any of the chemosensory measures. The isolated odor identification deficit suggests that the initial chemosensory impairment in AD is central rather than peripheral.