[Severe olfactory dysfunction is a predictor of dementia with Parkinson's disease]

Recently, we identified that hyposmia, one of the most typical non-motor features in Parkinson's disease (PD), was a predictive feature of PDD (Parkinson's disease dementia). The multivariate logistic analysis identified severe hyposmia and visuoperceptual impairment as independent risk factors for subsequent dementia within 3 years. The patients with severe hyposmia had an 18.7-fold increase in their risk of dementia for each 1 SD (2.8) decrease in the score of odor stick identification test for Japanese (OSIT-J). We also found an association between severe hyposmia and a characteristic distribution of cerebral metabolic decline, which was identical to the findings observed in PDD. Furthermore, volumetric magnetic resonance imaging analyses demonstrated close relationships between olfactory dysfunction and the atrophy of focal brain structures, including the amygdala and other limbic structures. Dementia is one of the most debilitating symptoms of PD. Despite its clinical importance, the development of dementia is still difficult to predict at early stages. As cognitive impairments are known to be associated with poor prognoses in PD, olfactory tests may be a useful tool for the management of PD cases especially in advanced stages.