title: Diagnostic value of the impairment of olfaction in Parkinson's disease.
abstract: BACKGROUND
  Olfactory impairment is increasingly recognized as an early symptom in the development of Parkinson's disease. Testing olfactory function is a non-invasive method but can be time-consuming which restricts its application in clinical settings and epidemiological studies. Here, we investigate odor identification as a supportive diagnostic tool for Parkinson's disease and estimate the performance of odor subsets to allow a more rapid testing of olfactory impairment.
  
  
  RESULTS
  Odor identification was assessed with 16 Sniffin' sticks in 148 Parkinson patients and 148 healthy controls. Risks of olfactory impairment were estimated with proportional odds models. Random forests were applied to classify Parkinson and non-Parkinson patients. Parkinson patients were rarely normosmic (identification of more than 12 odors; 16.8%) and identified on average seven odors whereas the reference group identified 12 odors and showed a higher prevalence of normosmy (31.1%). Parkinson patients with rigidity dominance had a twofold greater prevalence of olfactory impairment. Disease severity was associated with impairment of odor identification (per score point of the Hoehn and Yahr rating OR 1.87, 95% CI 1.26-2.77). Age-related impairment of olfaction showed a steeper gradient in Parkinson patients. Coffee, peppermint, and anise showed the largest difference in odor identification between Parkinson patients and controls. Random forests estimated a misclassification rate of 22.4% when comparing Parkinson patients with healthy controls using all 16 odors. A similar rate (23.8%) was observed when only the three aforementioned odors were applied.
  
  
  CONCLUSIONS
  Our findings indicate that testing odor identification can be a supportive diagnostic tool for Parkinson's disease. The application of only three odors performed well in discriminating Parkinson patients from controls, which can facilitate a wider application of this method as a point-of-care test.
authors.affiliation: German Social Accident Insurance, Institute of the Ruhr-Universität Bochum (IPA), Bochum, Germany.
authors.forename: Swaantje
authors.initials: S
authors.lastname: Casjens
authors.forename: Angelika
authors.initials: A
authors.lastname: Eckert
authors.forename: Dirk
authors.initials: D
authors.lastname: Woitalla
authors.forename: Gisa
authors.initials: G
authors.lastname: Ellrichmann
authors.forename: Michael
authors.initials: M
authors.lastname: Turewicz
authors.forename: Christian
authors.initials: C
authors.lastname: Stephan
authors.forename: Martin
authors.initials: M
authors.lastname: Eisenacher
authors.forename: Caroline
authors.initials: C
authors.lastname: May
authors.forename: Helmut E
authors.initials: HE
authors.lastname: Meyer
authors.forename: Thomas
authors.initials: T
authors.lastname: Brüning
authors.forename: Beate
authors.initials: B
authors.lastname: Pesch
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009812:Odorants / Q000032:analysis*; D000857:Olfaction Disorders / Q000175:diagnosis*; D010300:Parkinson Disease / Q000503:physiopathology*