Abstract
Olfactory dysfunction (OD) is a prominent nonmotor symptom in Parkinson's disease (PD), and OD is a supportive diagnostic criterion for PD. Physicians often ask their patients if they have noticed a smell disorder. This study evaluates the diagnostic validity of OD self-assessment in PD. To this end, 64 PD patients and 33 age-matched healthy controls were enrolled in a study assessing subjective and objective olfactory functioning. To examine subjective olfactory abilities, first, patients and controls had to classify their olfactory sense as “impaired” or “unimpaired,” comparable to a realistic situation in an outpatient setting. Second, to evaluate subjective olfactory acuity, a visual analogue scale (VAS) was used. Third, the Sniffin' Sticks test battery was used as an objective instrument to diagnose OD. Categorical olfactory self-assessment predicts the classification normosmic versus hyposmic based on the global Sniffin' Sticks score (TDI) with a sensitivity of 0.79 and a specificity of 0.45. TDI correlated significantly with the VAS (r = 0.297, p = 0.017). The ROC curve analysis, using the VAS rating as a predictor for objective olfaction, revealed 42 as the best possible cutoff score with an area under the curve of 0.63. These results demonstrate that olfactory self-assessments show a low accuracy and are not suitable for the diagnosis of a smell disorder in PD. Objective measures are necessary to evaluate olfactory sense in clinical and research settings.
Highlights
Olfactory dysfunction (OD) is a common nonmotor symptom in idiopathic Parkinson’s disease (PD)
We found low to moderate predictive values of self-reported OD in PD patients. ere were significant correlations between a subjective visual analogue scale (VAS) rating of olfactory abilities and an objective olfactory test battery
The relationship between the two measures was not strong enough to predict objective olfactory abilities by means of subjective evaluation. e insufficient quality of prediction rate is expressed by an area under curve that was barely above that of performance by chance. erefore, the information obtained from the question about subjectively experienced OD is not valid and uninformative
Summary
Olfactory dysfunction (OD) is a common nonmotor symptom in idiopathic Parkinson’s disease (PD). OD is a supportive criterion for PD according to the Movement Disorder Society clinical diagnostic criteria for Parkinson’s disease [1] and a relevant risk marker for prodromal PD with a positive likelihood ratio of 6.4 [2]. It plays a relevant role in the differential diagnosis of Parkinsonian syndromes [3]. Objective olfactory tests are timeconsuming, and many clinicians ask the patients for olfactory impairments and may trust in their subjective evaluation [4]. Is applies to some studies, when subjective olfaction rating was used instead of objective olfactory measures. Objective olfactory tests are timeconsuming, and many clinicians ask the patients for olfactory impairments and may trust in their subjective evaluation [4]. is applies to some studies, when subjective olfaction rating was used instead of objective olfactory measures. is approach seems questionable as it could be shown that self-reports of OD do not reflect objective OD in healthy controls [5,6,7,8,9]
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