Presbyosmia, Parkinson's and Pharmaceutically-induced loss of olfactory function

Abstract

Olfactory function is impaired in the majority of persons with Parkinson's disease (PD). Olfactory dysfunction occurs early in the disease and is a proposed means of premorbid disease detection. However, the level of olfactory impairment is not universal in PD patients. This variability may be attributed to differences in the Parkinson's disease process or other idiopathic variability resulting from unidentified age-associated health and medication effects, as seen in normative populations. We assessed olfactory function from patients with PD using the 'Sniffin' sticks' tests and compared these data to results collected from the healthy Australian population. We found little evidence of presbyosmia (age-associated idiopathic loss of smell) in the general population, when controlling for other factors such as history of medication and upper respiratory disease, and showed that many people with clinically diagnosed PD retain significant olfactory function, even compared with healthy age and sex-matched controls. We also found relatively little change in longitudinal olfactory function in PD patients, across an 18 month period, irrespective of the prior disease duration. Curiously, patients receiving different medications performed significantly differently, suggesting that medication status may exacerbate olfactory dysfunction in this patient group. This is particularly significant given the high rate of prescription of these drugs; more than 300,000 scripts (>$23 million) were issued in 2003 in Australia alone (PBS, Australia). These findings will be discussed in the context of non-neurological factors impacting on smell in an aging population.