Parkinson syndrome

Abstract

Genetic discoveries over the past 15 years indicate that distinct etiologic triggers can cause nigrostriatal degeneration. These discoveries indicate that Parkinson disease (PD) is actually a syndrome (Parkinson syndrome [PS]), a cluster of signs and symptoms associated with dysfunction of a specific organ or system. Differing etiologies can give rise to common syndromic features. Hepatic failure, for example, has genetic, toxic, and infectious causes. Similarly, the nigrostriatal degeneration associated with the defining motor features of PS—resting tremor, bradykinesia, and rigidity—can result from different genetic causes. There are also hints of heterogeneity in sporadic PS. Clinicians, for example, have long suspected that tremor-predominant PS has a more benign course than PS dominated by postural instability and gait disorder, the so-called PIGD variant. It is increasingly clear that several brain circuits degenerate in PS and there is evidence that subjects with PS may differ in the degree of involvement of nondopaminergic brain systems. For example, degeneration of corticopetal basal forebrain cholinergic projections is common in PS but imaging evidence from Shimada et al.1 shows relative sparing of this system in some subjects with longstanding sporadic PS.