Psychiatric Disorders in Parkinsonian Syndromes-Nuclear Medicine Contribution

Abstract

Parkinsonian disorders consist mostly of Parkinson’s disease (PD); other forms are relatively rare, although dementia with Lewy bodies (DLB) seems to be, after Alzheimer’s disease, one of the most common causes of dementia. Atypical parkinsonisms (other than idiopathic PD) include progressive supranuclear palsy (PSP), multiple system atrophy (MSA), corticobasal degeneration (CBD) and DLB. In addition to parkinsonism symptoms the most characteristic features of these disorders, sometimes called parkinsonism-plus syndromes, are cerebellar ataxia in MSA, apraxia in CBD, gaze palsy in PSP or early in the course of dementia in DLB, and minimal, sometimes moderate (in MSA or PSP) or complete lack (in CBD) of response to L-dopa therapy. When appraising the condition, it is vital to separate it from those conditions that mimic the appearance of PD, but that are caused by another underlying pathology. Because of the lack of biological markers, differential diagnosis has to be based mostly on clinical findings. Nevertheless, neuroimaging studies, utilizing MRI, SPECT and PET examinations, seem to be helpful in establishing diagnosis. Nuclear medicine uses different tracers, specific for the dopamine transporting system or dopamine receptor ligands, which makes it possible to differentiate presynaptic dopaminergic system involvement (seen in PD) from pre- and postsynaptic involvement in MSA or PSP. Highly asymmetric tracer uptake reflects the asymmetry of cortical-subcortical atrophy and is characteristic for CBD. All of these conditions are accompanied by different psychiatric problems. In PD, depression is the most common, followed by dementia and psychosis at late stages. In PSP, subcortical dementia is typical with frontal behavior. Dementia is less frequent and late in CBD, but usually is the first or early symptom in DLB, followed by parkinsonian features. Functional neuroimaging may be useful for assessment of the preclinical period of PD (with potential early neuroprotective therapy), the rate of progression (evaluation of the influence of drugs and stereotaxic surgery on disease progression), the role of different structures in late complications (dyskinesias, fluctuations), and differential diagnosis of PD with essential tremor and atypical parkinsonian disorders. These techniques may also be helpful for investigation of pathogenesis and pathology underlying the non-motor symptoms of PD and atypical parkinsonisms as depression, dementia and psychosis. This review summarizes recent applications of SPECT, PET, but also MRI in the study of parkinsonian disorders, in terms of differential diagnosis and understanding concomitant neuropsychiatric phenomena.