Odor identification as an early marker for Alzheimer's disease: Impact of lexical functioning and detection sensitivity

Abstract

The impact of lexical functioning and detection sensitivity on the deficit of odor identification in Alzheimer's disease (AD) was studied in persons diagnosed with probable and questionable AD. Tests consisted of lexical-based odor identification, lexical-based picture identification, picture-based odor identification, and odor-detection threshold. Results suggest (1) that odor identification is poorer than picture identification in probable and questionable AD, (2) that odor identification continues to be poor even when lexical demands are eliminated, (3) that odor detection does contribute to the odor-identification deficit, but does not account for it completely, and (4) that odor identification tests have a correct classification rate of 83-100%. Odor identification tests can be very useful tools in diagnosing AD and should be considered an important addition to existing diagnostic test batteries.

Left hippocampal volume loss in Alzheimer's disease is reflected in performance on odor identification: A structural MRI study

“…AD patients showed significantly impaired performance on the San Diego Odor Identification Test (M 5 27% correct) relative to controls (M 5 62%), replicating earlier work (Morgan et al, 1995). The patients also showed poorer performance on the Boston Naming Test (M 5 77%) relative to controls (M 5 96%).…”

“…This early vulnerability of the olfactory system to the neuropathology of AD has motivated our strategy to use olfactory functional testing to investigate Alzheimer's disease and to explore the potential for olfactory tests to contribute to detection of incipient dementia (Morgan et al, 1995;Murphy et al, 1990;Nordin & Murphy, 1996). Compared with young adults, normal older people show losses in odor sensitivity, odor intensity perception, odor identification, and odor memory (Murphy, 1983(Murphy, , 1993Murphy et al, 1991Murphy et al, , 1997Schiffman, 1997).…”

“…Even compared with these age-related losses in function, patients with Alzheimer's disease show dramatic impairment in olfactory function (Murphy, 1999). Patients with probable AD show very poor sensitivity to odor (Murphy et al, 1990), severe deficits in odor identification (Doty et al, 1987;Knupfer & Spiegel, 1986;Koss, 1986;Morgan et al, 1995;Murphy et al, 1998;Serby et al, 1985;Waldton, 1974), impaired odor fluency (Bacon et al, 1999), poor odor recall and recognition memory (Murphy et al, 1987;Niccoli-Waller et al, 1999;Nordin & Murphy, 1996), and slower processing of olfactory information reflected in event-related potentials (Morgan & Murphy, 2002). The results of this research strongly support the use of olfactory measures in the assessment of Alzheimer's disease.…”

“…The results of this research strongly support the use of olfactory measures in the assessment of Alzheimer's disease. Particularly high sensitivity and specificity for detecting Alzheimer's patients from controls has been demonstrated with odor identification or odor naming tests (Morgan et al, 1995;Morgan & Murphy, 2002;Murphy, 1999).…”

The human brain representation of odor identification

“…In the clinic OI tests have been shown to have high sensitivity and specificity for predicting Alzheimer's disease (AD) at an early stage. This OI deficit is considered a central phenomenon as olfactory threshold, detection, and discrimination abilities are preserved (Arnold et al 1998;Morgan et al 1995;Serby et al 1991;Wilson et al 2007Wilson et al , 2009. Since AD pathology is first observed in entorhinal cortex and subsequently in the hippocampus (Braak and Braak 1992), OI impairments may arise from medial temporal lobe (MTL) pathology.…”