Effect of olfactory impairment and white matter hyperintensities on cognition in Parkinson's disease.

Introduction: Although white matter hyperintensities (WMH) and olfactory dysfunction are independently associated with the cognitive impairments in Parkinson's disease (PD), the effects of simultaneous presence of these abnormalities remain unknown. Thus, we investigated the different effects of deep WMH and periventricular WMH on olfactory and cognitive performance and evaluated the additive effects of the concurrent presence of WMH and olfactory dysfunction on cognitive performance in PD.

Methods: We enrolled 171 patients with non-demented PD whose WMH scores were assessed using a semi-quantitative visual rating system. The olfactory and cognitive performance was assessed using the Cross-Cultural Smell Identification (CCSI) test and the Seoul Neuropsychological Screening Battery. Additionally, the additive effects of concurrent WMH and olfactory dysfunction on cognitive performance were investigated using binary logistic regression.

Results: The deep WMH score exhibited a significant negative correlation with the CCSI score (p = 0.026) but the total WMH and periventricular WMH did not. A multiple regression analysis revealed that the total WMH (β = -0.109, p = 0.011) and deep WMH (β = -0.153, p = 0.020) severities had significant negative correlations with semantic fluency. A logistic regression analysis revealed that the simultaneous presence of severe olfactory dysfunction and deep WMH was associated with a greater risk for the semantic fluency impairments (odds ratio = 15.909, p = 0.0005) compared to patients with mild deep WMH or high CCSI scores.

Conclusions: These data indicate that deep WMH was closely coupled with olfactory impairments and cognitive decline in PD. Moreover, the concurrent presence of severe deep WMH and olfactory impairments has a greater influence on semantic fluency.