Awareness of Olfactory Dysfunction in Parkinson's Disease

Objective: Olfactory impairment is a very common symptom in Parkinson's disease (PD). However, individuals often overestimate their ability to smell. Hyposmia and metacognitive errors are also related to aging, depression, male gender and cognitive impairment. The current study investigated the awareness of olfactory functioning in PD and the influence of additional factors. Method: A sample of 124 nondemented PD patients and 154 elderly controls was assessed with the Sniffin' Sticks Odor Identification Test (OIT) and the Subjective Olfactory Capability (SOC) domain of the Assessment of Self-Reported Olfactory Functioning and Olfaction-Related Quality of Life, additional to measures of depressive symptoms, verbal memory and executive functioning. Olfactory awareness groups were formed by means of the cut-offs of the OIT and the SOC. Results: Significant correlations between the OIT and the SOC were moderate in participants with PD and small in controls. Of all PD patients, 52% overrated their sense of smell while 27% correctly identified themselves as being hyposmic. as opposed to corresponding 6% and 1% of healthy elderly. Overrating and aware of being hyposmic participants with PD showed worse executive functions than PD patients who were objectively and subjectively normosmic. Conclusions: The findings imply that, although people with PD are aware of hyposmia to some extent, the majority is affected by overestimation of the ability to smell, making self-reported functioning an unreliable source of information. Moreover, reduced odor identification and impaired executive functioning might underlie the same pathological changes within the brain and could serve as a marker for cognitive impairment in PD.