Chronic delusional hallucinatory psychosis in early-onset Parkinson's disease: drug-induced complication or sign of an idiopathic psychiatric illness?

Chronic delusional psychosis with hallucinations (CDHP) is commonly assumed to complicate the later stages of Parkinson's disease, as a side effect of antiparkinsonian medication. We studied 7 patients with early onset PD, who had developed psychiatric manifestations consisting in CDHP after a few years of antiparkinsonian therapy. All patients underwent a neurological, psychiatric and brain imaging (CT or MRI) evaluation. Detailed clinical history was recorded in order to reveal prior psychiatric illness and to analyse the relationship between neurological disease, cognitive impairment and psychosis. Our findings suggest that CDHP occurring in patients with early onset PD, normal or slightly impaired cognitive functions and normal CT/MRI scans is invariably the expression of a coexisting psychiatric illness which prior to onset of the neurologic disease had not been correctly diagnosed and which has been disclosed by dopaminergic therapy.