title: An olfactory 'stress test' may detect preclinical Alzheimer's disease.
abstract: BACKGROUND
  The olfactory bulb (OB) receives extensive cholinergic input from the basal forebrain and is affected very early in Alzheimer's disease (AD). We speculated that an olfactory 'stress test' (OST), targeting the OB, might be used to unmask incipient AD. We investigated if change in olfactory performance following intranasal atropine was associated with several known antecedents or biomarkers of AD.
  
  
  METHODS
  We measured change in performance on the University of Pennsylvania Smell Identification Test (UPSIT) in the left nostril before (20-items) and after (remaining 20-items) intranasal administration of 1 mg of atropine. We administered cognitive tests, measured hippocampal volume from MRI scans and recorded Apolipoprotein E genotype as indices relevant to underlying AD.
  
  
  RESULTS
  In a convenience sample of 56 elderly individuals (14 probable AD, 13 cognitive impairment no dementia, 29 cognitively intact) the change in UPSIT score after atropine ('atropine effect' = AE) correlated significantly with demographically scaled episodic memory score (r = 0.57, p < 0.001) and left hippocampal volume (LHCV) (r = 0.53, p < 0.001). Among non-demented individuals (n = 42), AE correlated with episodic memory (r = 0.52, p < 0.001) and LHCV (r = 0.49, p < 0.001) and hierarchical linear regression models adjusted for age, gender, education, and baseline UPSIT showed that the AE explained more variance in memory performance (24%) than did LHCV (15%). The presence of any APOE ϵ4 allele was associated with a more negative AE (p = 0.014).
  
  
  CONCLUSIONS
  The OST using atropine as an olfactory probe holds promise as a simple, inexpensive screen for early and preclinical AD and further work, including longitudinal studies, is needed to explore this possibility.
authors.affiliation: Neuropsychiatry service, Hunter New England Area Health, Newcastle, Australia. peter.schofield@hnehealth.nsw.gov.au
authors.forename: Peter W
authors.initials: PW
authors.lastname: Schofield
authors.forename: Houman
authors.initials: H
authors.lastname: Ebrahimi
authors.forename: Alison L
authors.initials: AL
authors.lastname: Jones
authors.forename: Grant A
authors.initials: GA
authors.lastname: Bateman
authors.forename: Sonya R
authors.initials: SR
authors.lastname: Murray
mesh_terms: D000281:Administration, Intranasal; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000175:diagnosis* / Q000503:physiopathology*; D001285:Atropine / Q000008:administration & dosage*; D042241:Early Diagnosis; D005260:Female; D006801:Humans; D008297:Male; D009830:Olfactory Bulb / Q000187:drug effects* / Q000503:physiopathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012903:Smell / Q000187:drug effects*
chemical_list: D001285:Atropine