Neuropsychological Functions and SPECT Neuroimaging in Parkinson’s Disease

Abstract

Parkinson’s disease (PD) is a chronic progressive neurodegenerative disorder, characterized by motor and non-motor signs. It was Charcot, who first in 1875 pointed out that ‘psychic faculties are definitely impaired’ and that ‘the mind becomes clouded and the memory is lost’. Most patients with PD experience some degree of cognitive impairment, ranging from mild selective deficits to Parkinson’s disease dementia (Dubois & Pillon, 1997). PD patients may also spend several years in a transition state called Mild Cognitive Impairment (MCI), which is now recognized as one of the cardinal non-motor manifestations of PD. It is a major cause of disability, and has been shown to be an important predictor for quality of life (Karlsen et al., 1998). Recent studies have reported a 21% prevalence rate of MCI in a large PD population and consider MCI as a risk factor for developing Parkinson’s disease Dementia (PDD) (Caviness et al., 2007; Janvin et al., 2006; Levin et al., 1992). The neuropathophysiological basis of cognitive deficits in PD is complicated and includes degeneration of dopaminergic neurons mainly of the nigrostriatal pathway and to a lesser degree the mesocortical and mesolimbic pathways. The striatum is closely interrelated to cortical areas mainly to the frontal lobes. The neuropathophysiological puzzle is further complicated by multiple neurotransmitter deficits including noradrenalin, serotonin and acetylcholine pathway as well as Lewy bodytype degeneration in cortical and limbic structures (Mandir & Vaughan, 2000). The direct dopaminergic connections between the ventral tegmental area and the prefrontal cortex may also influence changes in cognition (Cools 2006; Mattay et al., 2002). The pattern of cognitive impairment seen even in early PD mainly resembles that produced by frontal lobe damage, as the basal ganglia and prefrontal cortex are closely interrelated through anatomofunctional circuits (Alexander et al., 1986; Bondi et al., 1993) and include deficits mainly in cognitive flexibility, planning, working memory and learning. Perfusion brain single photon emission computed tomography (SPECT) provides a wellestablished means of studying regional cerebral blood flow (rCBF) which is known to reflect cortical function. On the other hand Dopamine Transporter (DAT) SPECT imaging can be used as a marker for the degree of loss of dopaminergic nerve endings. It is well known that SPECT Neuroimaging can assist in the differential diagnosis of parkinsonian and dementia