Loss of Smell in Parkinson’s Disease Increases Risk of Dementia

The loss of smell is a common symptom in LBD, Parkinson’s disease and even Alzheimer’s disease. New research suggests the loss of smell in Parkinson’s disease (PD) may help predict who will go on to develop Parkinson’s disease dementia (PDD), one form of Lewy body dementia.

Researchers in Sweden followed a group of 125 people newly diagnosed with PD for up to 10 years. Baseline assessments included motor, cognitive and mood symptoms, the ability to smell; DaTscans were performed as well. Neuropsychological assessments and smell tests were done at baseline, one, three, five and eight-year study visits. In this cohort, 91 people (73%) had some loss of smell at the start of the study.

Of those with smell loss, 42 progressed to dementia. A combination of mild cognitive impairment plus smell loss was found in 40 people, 65% of whom progressed to dementia. Researchers found that loss of smell at baseline increased the risk of developing dementia three times, regardless of baseline cognitive function.

Of importance, self-reported loss of smell did not predict progression to dementia. This is supported by another recent study that found people with Parkinson’s and mild cognitive impairment were more likely to rate their sense of smell as better than it actually is.

While this study highlights the important predictive value that loss of smell plays in those who developed dementia in Parkinson’s disease, there was good news as well. Only 5% of the 22 people who had neither MCI or smell loss developed dementia during the study. Having normal smell at baseline was a good predictor of maintaining stable cognitive function the first five years after diagnosis.

This study was published in February, 2017 in Parkinsonism and Related Disorders.