Parkinson’s disease is the second most prevalent neurodegenerative disorder affecting 1% of the population above the age of 60. Mild cognitive impairment is frequent in Parkinson’s disease and is often associated with an increased risk of subsequent dementia. However, it is difficult to predict if a patient with Parkinson’s disease and mild cognitive impairment will progress to Parkinson’s disease with dementia at the individual level because the mechanisms of mild cognitive impairment are heterogeneous in Parkinson’s disease. Furthermore, atypical parkinsonism, especially tau parkinsonism, may accompany cognitive impairment. Therefore, clinical diagnosis of a patient presenting with parkinsonism and cognitive impairment is not straightforward.

Only symptomatic relief is available via drugs that were originally developed to target dementia associated with Alzheimer’s; no disease-modifying treatment targeting Parkinson’s cognitive deficit is yet available. A lack of validated biomarkers and incomplete understanding of underlying mechanisms have hindered therapy discovery.

In some patients, cognitive decline will be rapid, while others can remain cognitively stable even over extended disease durations. Importantly, future disease-modifying interventions for cognitive deterioration are likely to be most effective if applied at very early disease stages, before cognitive symptoms develop. Yet, we do not have an accurate method to predict future dementia in individuals. As such, the search for a biomarker to predict future cognitive deterioration is an area of highly active research, with recent reports suggesting that a combinatorial algorithm—incorporating cognitive and motor clinical profiles, neuroimaging, and molecular and genetic markers—will be more successful than any one biomarker alone.

In this special issue, we welcome research studies and/or reviews on this topic. Studies about biomarkers that predict the development of dementia or mild cognitive impairment in Parkinson’s disease are especially welcome. Studies that compare different types of dementia with Parkinson’s disease dementia, e.g., dementia with Lewy Bodies, Alzheimer’s disease, and other atypical parkinsonian syndromes, are also encouraged.

Potential topics include but are not limited to the following:

• Cognitive profiles in early Parkinson’s disease that are associated with future dementia
• Neuroimaging studies revealing the neurodegenerative changes that accompany increasing cognitive deterioration
• Animal models of cognitive impairment in Parkinson’s disease
• Biomarkers that predict dementia development in Parkinson’s disease
• Comparative studies investigating similarities and differences between Parkinson’s vs. other types of dementia (e.g., Alzheimer’s)
• Neuroimaging and/or neuropsychological studies investigating the subtypes of cognitive deficits in Parkinson’s disease