Parkinson’s disease progression and fronto-temporal disconnection relate to identity of minor hallucinations

Presence hallucinations (PH), a non-veridical perceptions of someone appearing around you, are frequent symptoms in Parkinson’s disease (PD). They belong to the group of minor hallucinations, predicting later appearance of structured visual hallucinations and PD psychosis. Despite their elevated frequency and negative clinical outcomes, differences in PH subtypes have not been examined. Investigating PD patients with identified versus unidentified PH, this study aims to determine differences in disease progression, motor and cognitive performance, and brain mechanisms. From 77 PD patients, 27 reporting PH were grouped into those with identified PH versus unidentified PH (iPH-PD, n = 12; uPH-PD, n = 15). Disease progression (UPDRS, Hoehn Yahr), cognitive functions (PD-CRS) (with exploratory analysis of all clinical variables, uncorrected for multiple comparisons), sensitivity to robot-induced PH and resting-state functional connectivity were analysed. iPH reports mostly consisted of first-degree close others (e.g., partner). iPH-PD patients had a more advanced PD stage, reported more daily-life motor impairments and simple visual illusions than uPH-PD patients. Both groups showed similar sensitivity to robot-induced PH. Resting-state functional connectivity showed that iPH-PD vs. uPH-PD patients had right IFG-pMTG functional disconnection within a previously defined PH network and the degree of this disconnection correlated with posterior cognitive impairment. Distinguishing iPH-PD from uPH-PD patients, we show that the former display worse daily motor functioning, more frequent visual illusions and stronger fronto-temporal disconnection, related to cognitive dysfunction. Although the present findings need to be confirmed in larger samples, they suggest that iPH-PD have a more advanced form of PD, possibly representing an intermediate disease stage, between uPH-PD and PD patients with structured visual hallucinations.