Odor identification deficits are associated with increased risk of neuropsychiatric complications in patients with Parkinson's disease.

Olfactory deficits appear early in the course of Parkinson's disease (PD) but their prognostic significance is not known. The goal of this study was to determine whether the severity of olfactory impairment is associated with subsequent risk of developing complications of PD. One hundred patients with PD self-administered the University of Pennsylvania Smell Identification Test (UPSIT). Testing was done, on average, 3.6 years from the time of initial diagnosis. The incidence of neuropsychiatric features of PD, including cognitive decline and visual hallucinations, was ascertained through chart review after an average of 6.8 years of follow-up. Incidence of motor outcomes including falls and dyskinesias was also obtained. There was a significant trend for increased risk of neuropsychiatric complications across declining quartiles of olfactory test scores. In addition, subjects in the lowest quartile of olfactory performance had a significantly higher adjusted risk of hallucinations (HR = 4.70, 95% CI 1.64, 13.42) and cognitive decline (HR = 3.10, 95% CI 1.05, 9.21) than those in the reference quartile. There was no association between olfactory dysfunction and dyskinesias, and a very modest association with risk of falls. These findings suggest that severity of olfactory impairment early in the disease course may be a useful marker for the risk of neuropsychiatric complications of PD.