Olfactory dysfunction in Parkinson’s disease: Benefits of quantitative odorant examination

Olfactory involvement is well recognized in patients with Parkinson's disease (PD). The purpose of this study was to examine smell function quantitatively, using different types and concentrations of odorants in PD patients. We aimed to elucidate whether a specific odor can affect the severity and duration of PD patients. A total of 89 nondemented PD patients and 20 age-matched controls participated in the study. Quantitative evaluation of smell function was performed using the T and T olfactometer test. This test contains five kinds of odorants at different concentrations. Recognition threshold (RT) scores for all five odorants and for each individual odorant were measured in five groups of PD patients with Hoehn and Yale (HY) stages I (n = 12), II (n = 24), III (n = 43), and IV (n = 10), as well as in control subjects (n = 20). One-way analysis of variance and Ryan's method were used for statistical comparison between the five groups. Compared with controls and HY I patients, total RT scores were significantly higher in HY II, III, and IV patients. There were no statistically significant differences in RT scores between HY I patients and controls. However, total RT scores for three HY I patients (25%) were higher than the mean + two standard deviations of controls. On single odorant testing, significant higher RT scores for methylcyclopentenolone and skatol were found in HY II, III, and IV patients, in comparison with controls and HY I patients. The remaining three odorants did not differ statistically between PD patients and control subjects. The present study indicated that hyposmia in PD patients increased from HY II onwards. A single odorant of methyl cyclopentenolone or skatol had benefits for olfactory evaluation in PD patients. Our data also clarified that olfactory deficits occurred in a subset of HY I patients. Further prospective study is needed to elucidate whether a distinct profile of PD exists between HY I patients with and without hyposmia.