Identifying the Pattern of Olfactory Deficits in Parkinson Disease Using the Brief Smell Identification Test

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Abstract
SEVENTY PERCENT to 90% of patients with Parkinson disease (PD) have olfactory deficits1 independent of disease severity and duration.2 Olfactory dyfunction is thus the second most common feature of this disorder, following rigidity and akinesia, and is equal to the occurrence of tremor.3 The identification of a common and early hyposmia in PD4 has led to an interest in olfactory testing as a diagnostic aid.1,5 Hyposmia in PD is generally bilateral, even in early hemiparkinsonism, and remains unaffected by parkinsonian medication.6 Tests of olfaction are commonly based on total olfactory performance after exposure to multiple odors. Although patients with PD perform significantly more poorly with the use of this criterion,1,2,5 more detailed analyses have shown that the olfactory deficit in PD is not general for all odors. Thus, the ability to detect some odors remains unchanged, while the ability to identify other odors is significantly impaired in patients with PD compared with control subjects. For example, the ability to identify the odors of orange and clove is reportedly preserved in PD1; in contrast, the ability to identify the odors of wintergreen, pizza,4 pineapple, anise seed, and licorice1 is highly compromised. The selectivity of odor detection demonstrated by different olfactory tests suggests a distinct and identifiable pattern of hyposmia in PD. Characterization of this pattern may allow the development of more accurate diagnostic olfactory tests, compared with the assessment of general olfactory function.

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