Delusional infestation in Parkinson disease: a case report of medication-induced psychosis

Delusional infestation (DI) is an uncommon manifestation of psychosis in Parkinson disease (PD), and is often associated with dopaminergic therapy. We describe a 66-year-old woman with PD who developed visual and tactile delusions of a parasitic infestation while receiving dopaminergic medications. Comprehensive neuropsychological testing revealed largely preserved cognitive functioning, with only mild relative weaknesses in processing speed and problem-solving. The patient's symptoms resolved following discontinuation of amantadine, supporting an iatrogenic etiology. Previous case reports have consistently described a link between DI and dopaminergic overstimulation, although DI has been observed across a broad range of cognitive functioning. This case highlights the diagnostic utility of formal neuropsychological assessment and underscores the importance of recognizing DI as a potentially reversible, iatrogenic phenomenon within the spectrum of PD psychosis.