Diagnosis and differential diagnosis of Parkinson's disease and parkinsonism.

In the clinic setting, most cases represent either Parkinson's disease (PD) or one of the other neurodegenerative disorders that make up the parkinsonism-plus syndromes. The major parkinsonism-plus syndromes include progressive supranuclear palsy, multiple system atrophy, corticobasal degeneration, as well as parkinsonism occurring in the context of Alzheimer's disease or one of the other primary dementing disorders. There are a variety of other conditions, however, that occasionally come into the differential diagnosis. These fall into the categories of secondary parkinsonism (due to drugs, toxins, structural lesions, etc.), another tremor syndrome such as essential tremor, or a hereditary disorder with parkinsonism. This broad differential diagnosis is reviewed.