Paranoia and unusual sensory experiences in Parkinson's disease.

Objectives: There has been limited exploration into the nature and development of psychotic experiences (PEs) in Parkinson's disease (PD). We aimed to comprehensively assess the frequency, severity, and associated distress of paranoia and unusual sensory experiences (USEs) in PD, and to assess what variables are significantly associated with these experiences, focussing on psychological processes central to understanding PEs in non-PD groups.

Method: A questionnaire battery was completed by 369 individuals with PD with a mean age of 66 years and mean time since diagnosis of 5 years. Recruitment was via Parkinson's UK, social media, and local community groups. For a subset of measures, comparisons were made to age-matched controls using pre-existing data.

Results: 182 (49%) participants reported USEs, including almost half of those not taking dopaminergic medication. For 83 (23%), the experience was distressing. Paranoia across the sample was significantly lower than in age-matched controls. However, specific paranoid concerns around abandonment (16%) and spousal betrayal (10%) were reported by some. Depression, anxiety, loneliness, and stigma and desire for support with PEs were high across the sample. Almost all psychological variables were significantly associated with PEs in structural equation models.

Conclusion: PEs in PD are common, even in those not taking dopaminergic medication. For a small subset, these experiences are distressing and not resolved by existing treatment. Cognitive-affective variables like depression and anxiety could play a maintaining role in PEs in PD thus providing easy avenues for trialling intervention.