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

Presence hallucinations (PH), non-veridical perceptions of someone appearing around you, are frequently occurring symptoms, in Parkinson’s disease (PD). They belong to the group of minor hallucinations and are predictors of the 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. Objectives Investigating PD patients with identified versus unidentified PH, this study determines differences in disease progression, motor and cognitive performance, and brain mechanisms. Methods Based on detailed interviews of 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), sensitivity to robot-induced PH and resting-state functional connectivity were analysed. Results 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 more simple visual illusions than uPH-PD patients. Both groups showed similar sensitivity to robot-induced PH. Resting-state functional connectivity showed that iPH-PD patients vs. uPH-PD patients had right IFG-pMTG functional disconnection within a previously defined PH-network and the degree of this disconnection was correlated with posterior cognitive impairment. Conclusion 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. These data 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.