Olfactory function in mild cognitive impairment and Alzheimer's disease: an investigation using psychophysical and electrophysiological techniques.
OBJECTIVE
To clarify the olfactory deficit hypothesis regarding Alzheimer's disease, the authors compared olfactory function in patients with Alzheimer's disease, subjects with mild cognitive impairment, and healthy comparison subjects.


METHODS
Olfactory function of 14 patients with mild Alzheimer's disease, eight subjects with mild cognitive impairment, and eight healthy age-matched comparison subjects was assessed with both psychophysical tests and olfactory event-related potentials.


RESULTS
Group comparison of the psychophysical test results showed a significant main effect of diagnosis for odor detection threshold, odor discrimination, and odor identification. These results correlated only partially with those obtained from olfactory event-related potentials. Seven Alzheimer's disease patients and four with mild cognitive impairment showed no olfactory event-related potentials, suggesting hyposmia, while all comparison subjects had clearly discernible responses. Patients with Alzheimer's disease were significantly more likely to be nonresponders. In the four Alzheimer's disease patients and four subjects with mild cognitive impairment who had clear electrophysiological responses, amplitudes and latencies of the various event-related potential components were normal, i.e., similar to those of the comparison subjects, although 12 of the 14 Alzheimer's disease patients and seven of the eight mildly impaired subjects were classified as functionally anosmic with psychophysical methods.


CONCLUSIONS
The electrophysiological results confirm prior findings of olfactory dysfunction in patients with Alzheimer's disease and preclinical Alzheimer's disease. Investigations of larger study groups with detailed cognitive examination and postmortem diagnosis may resolve the intriguing possibility of early diagnosis and discrimination of Alzheimer's disease subtypes through chemosensory event-related potentials in addition to existing biomarkers.
Department of Psychiatry and Psychotherapy I, University Hospital, Johann Wolfgang Goethe-University of Frankfurt am Main, Heinrich-Hoffmann-Strasse 10, 60528 Frankfurt am Main, Germany. juergen.peters@em.uni-frankfurt.de
Jürgen M
JM
Peters
Thomas
T
Hummel
Tilman
T
Kratzsch
Jörn
J
Lötsch
Carsten
C
Skarke
Lutz
L
Frölich
D000368:Aged; D000375:Aging / Q000502:physiology; D000544:Alzheimer Disease / Q000175:diagnosis* / Q000503:physiopathology / Q000523:psychology; D015415:Biomarkers; D002245:Carbon Dioxide / Q000494:pharmacology; D003072:Cognition Disorders / Q000175:diagnosis* / Q000503:physiopathology / Q000523:psychology; D004594:Electrophysiology / Q000379:methods; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D006862:Hydrogen Sulfide / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D000857:Olfaction Disorders / Q000175:diagnosis* / Q000503:physiopathology; D009833:Olfactory Pathways / Q000503:physiopathology; D011569:Psychiatric Status Rating Scales; D011601:Psychophysics / Q000379:methods; D012684:Sensory Thresholds / Q000502:physiology; D012720:Severity of Illness Index; D012903:Smell / Q000187:drug effects / Q000502:physiology*
D015415:Biomarkers; D002245:Carbon Dioxide; D006862:Hydrogen Sulfide