A clinical approach towards smell loss in Parkinson's disease

Impairment of olfaction is a characteristic feature of Parkinson's disease (PD). Recent data indicate that >90% of patients with PD are diagnosed with significant olfactory loss. The olfactory loss in PD has a bilateral and general character and all olfactory domains are involved. By clinical measurements, the olfactory deficit in PD is independent of disease severity and duration. Imaging studies however, point out that the olfactory impairment may be progressive in the early motor stages. Deficits in the sense of smell may precede clinical motor symptoms by years and can be used to assess the risk for developing PD in otherwise asymptomatic individuals. Numerous studies suggest that olfactory disturbances in PD may have diagnostic utility for the differentiation of PD from other movement disorders. This review summarizes the available information about the character of olfactory function in PD and possible therapeutic strategies. It indicates the advantageous use of olfactory probes as a contribution to early and differential diagnosis.