Association Between Olfactory Impairment and Disease Severity and Duration in Parkinson's Disease.

Abstract

The association between olfactory dysfunction and disease duration and severity in Parkinson's disease (PD) remains controversial. The objective of this study was to examine the relationship between olfactory dysfunction and disease severity and duration in patients with recently diagnosed parkinsonism and patients with PD with a previous diagnosis. Olfactory function was evaluated in 79 patients with recently diagnosed parkinsonism, 71 patients with PD with a previous diagnosis-with patients in both groups free of cognitive impairment-and 128 age-matched controls. The Odor-Stick Identification Test for Japanese score was counted as the numbers of correct answers, responses of indistinguishable, and responses of odorless. Parkinsonism was evaluated using the Movement Disorder Society Criteria, the Unified Parkinson Disease Rating Scale (UPDRS) Part III, and 123iodine-labeled N-(3-fluoropropyl)-2β-carbomethoxy-3β-(4-iodophenyl) nortropane single photon emission computed tomography (DaTscan). In the patients with recently diagnosed parkinsonism having the UPDRS Part III score ≥5 (mean [standard deviation: SD] score: 6.3 [1.9]) and with a positive DaTscan, the mean (SD) numbers of correct answers, responses of indistinguishable and responses of odorless were 4.3 (2.2), 1.6 (2.0), and 1.2 (2.2), respectively. In patients with PD with a previous diagnosis (mean [SD] UPDRS Part III score: 10.9 [3.2]), these numbers were 2.5 (2.2), 2.2 (2.5), and 3.8 (4.6), respectively. The patients with PD with a previous diagnosis showed more significant deterioration than the patients with recently diagnosed parkinsonism in the numbers of correct answers and responses of odorless (P < 0.0001). Olfaction in the combined patient group was significantly impaired compared with age-matched controls in each category (P < 0.0001). These findings imply a close association between olfactory dysfunction and disease severity and duration in PD.