Basal Forebrain Volume and Concurrent Hallucinations and Mild Cognitive Impairment in Parkinson's Disease

Visual hallucinations (VH) and mild cognitive impairment (MCI) often co-occur in Parkinson's Disease (PD). Each symptom in isolation is associated with cholinergic basal forebrain (BF) atrophy. However, it is unclear whether BF integrity relates to one symptom preferentially or to their co-occurrence, and whether this relationship is specific to the nucleus basalis of Meynert (Ch4 & Ch4p) or extends to other BF nuclei (Ch1-2 & Ch3).

To bridge the literature on MCI, VH, and the BF by examining associations between total and subregional BF volumes with VH, MCI, and concurrent symptomology.

We used clinical and structural MRI data in PD patients (n = 296), evaluated prior to deep brain stimulation. PD-MCI was identified in 61% of patients, VH in 25%, and symptoms co-occurred in 21% of the sample. We conducted logistic regressions to examine the relationships between BF volumes (total BF, Ch1-2, Ch3, Ch4, and Ch4p) with MCI, VH, and their combination, accounting for potential confounders (age, sex, LEDD, dopamine agonist, and anticholinergic medications).

Total BF, Ch1-2, and Ch4 volumes are negatively associated with the likelihood of PD-MCI, but not VH when the other symptom type is not considered. When both symptoms are considered, Total BF and Ch4 volumes are negatively related to the co-occurrence of MCI and VH relative to neither symptom.

Our data support the "cholinergic phenotype" in that BF atrophy, including Ch4, is associated with concomitant MCI and VH. Ch1-2 volume is further associated with MCI, which is interesting given its temporal lobe projections.