Fiber-specific white matter reductions in Parkinson hallucinations and visual dysfunction

Area of Science:

• Neuroimaging
• Neuroscience
• Neurology

Background:

• Parkinson disease (PD) is associated with visual disturbances, including hallucinations and reduced visual performance.
• White matter integrity is crucial for visual processing and cognitive function.
• Understanding the neurobiological underpinnings of visual symptoms in PD is vital for developing targeted interventions.

Purpose of the Study:

• To investigate microstructural and macrostructural white matter changes associated with visual hallucinations and low visual performance in Parkinson disease.
• To identify specific white matter tracts affected in PD patients with visual disturbances.

Main Methods:

• Fixel-based analysis (FBA), a novel diffusion MRI technique, was employed to assess white matter integrity.
• FBA metrics including fiber density (FD), fiber bundle cross-section (FC), and combined FD and FC (FDC) were analyzed.
• Data were collected from 105 PD patients (34 low visual performers, 19 hallucinators) and 35 age-matched controls.

Main Results:

• Parkinson disease patients with hallucinations showed reduced FC in the splenium of the corpus callosum and left posterior thalamic radiation.
• Significant reductions in the combined FDC metric (>50%) were observed in the splenium of PD hallucinators.
• PD patients with low visual performance exhibited widespread microstructural and macrostructural changes in several white matter tracts, including the corpus callosum and posterior thalamic radiations.

Conclusions:

• Specific white matter tract degeneration, particularly in posterior thalamic tracts, is evident in Parkinson disease patients with hallucinations and low visual performance.
• These findings provide mechanistic support for attentional models of visual hallucinations in PD.
• The study highlights the utility of FBA in characterizing white matter alterations in neurodegenerative diseases.