Parkinson's disease (PD), PD dementia (PDD) and dementia with Lewy body (DLB), collectively termed Lewy body disease (LBD), characterize an array of emotional, neurobehavioral and cognitive symptoms. Pure psychiatric presentation (PPP) of LBD is the fourth subtype of LBD in which psychiatric symptoms lasted for many years in the absence of neurological disturbance.

The aim of this study is to localize the PPP and its clinical characteristics in subjects with low uptake of myocardial metaiodobenzylguanidine (MIBG) study.

Sixty MIBG-verified patients (28 women and 32 men) were grouped into three psychiatric pictures; depression (group D: 27 patients), isolated visual hallucinations (group V: 16 patients) and psychotic picture (group P: 17 patients). Fifty six cases were examined with cerebral single photon emission tomography study. Thirty-seven cases had hypoperfusion regions and 19 cases showed no abnormality. Final diagnoses of PD, PDD, DLB and PPP were evaluated with an aid of DSM-IV-TR, UPDRS part III, the Hoehn and Yahr Scale, MMSE and the movement disorder society task force diagnostic criteria.

Three clusters, PDD and Group P, DLB and Group V, and Group D and PPP-PD were found significantly with correspondence analysis. UPDRS average score showed negative correlation with average MMSE scores. All patients with PPP and majority of patients with PD featured depression.

PPP subjects are considered to be incidental LBD or depression of pre-motor PD. Psychotic parkinsonian features contributed highly to dementia of LBD, and visual hallucination was closely associated with DLB.