Olfaction in Parkinson's Disease and Aging

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Olfactory dysfunction is common in patients with Parkinson's disease (PD) and has been reported to be caused by early pathological deposition of Lewy bodies and Lewy neuritis in the olfactory areas. However, olfactory function in PD does not have a linear relationship with PD duration and with the level of other symptoms. For predicting disease onset and commencing treatment before classic signs of the disease appear, it is important to know the relationship between the degree of olfactory impairment and the duration of the disease, and between olfactory deficit and aging. In the present study, we tested odor detection acuity and odor recognition acuity in PD patients and age-matched controls to determine the relationship between olfactory test scores and aging in PD. All PD patients were able to detect odors similar to normal subjects, but had difficulty recognizing odor. However, odor recognition was better in younger PD patients. We found a positive correlation between recognition scores and age in PD patients, indicating that odor recognition in PD patients declined with age even if the patients' severity of symptoms remained the same. We have not investigated the relationship between levels of brain activation in the memory-related areas such as the entorhinal cortex and the hippocampus and age during odor recognition in PD patients; however, there might be additional pathological changes, such as olfactory dopaminergic status in the hippocampus, involved in age-related olfactory deficit in PD patients.