Idiopathic Parkinson's disease (PD) is the most common cause of parkinsonism, accounting for about 75% of all cases. Other causes of parkinsonism include multiple system atrophy (MSA), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and a variety of other neurodegenerative disorders in which rest tremor, bradykinesia, rigidity, and other parkinsonian features are present. Since these disorders are often associated with other neurological deficits, such as dysautonomia (in MSA), vertical ophthalmoparesis (in PSP), and apraxia (in CBD), they are referred to as "parkinsonism plus syndromes." Whereas the above disorders are degenerative in nature, there are other forms of parkinsonism, which are secondary to a variety of etiologic factors including vascular parkinsonism (VP), hemiatrophy hemiparkinsonism, and toxic and metabolic causes.
It is important to review the cardinal features of PD that form the basis for diagnosis of parkinsonism. Cardinal motor features of PD are tremor, rigidity, bradykinesia, and postural instability. While these may occur in idiopathic PD, the atypical parkinsonian sydromes have a combination of these features in addition to the clinical features typical for each specific disorder. Proposed diagnostic criteria for PD include definite, probable, and possible PD and all of these require sustained response to levodopa (1). Although it is difficult to apply uniform diagnostic criteria to all the atypical parkinsonian syndromes, most of them share a common feature of poor or no response to levodopa. In this review we will discuss VP, and a variety of nondegenerative atypical parkinsonian syndromes (Table 1).
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