Differential diagnosis of Parkinson's disease and atypical parkinsonian disorders by magnetic resonance imaging.

Magnetic resonance imaging (MRI) is not usually considered helpful for establishing the diagnosis of Parkinson's disease, but it is much more important to support the clinical diagnosis in atypical parkinsonian disorders. In multiple system atrophy with predominant parkinsonian features (MSA-P), MRI demonstrates putaminal abnormalities due to loss of neurons and gliosis and accumulation of iron in the posterior lateral part of the nucleus. When cerebellar features are present (MSA-C), pontine and cerebellar atrophy is seen with signal abnormalities that correspond to the distribution of the degenerative changes. In progressive supranuclear palsy, the main abnormality is atrophy of the midbrain. Mild-to-moderate cerebral atrophy may be present, but more-marked asymmetrical atrophy in the posterior frontal and parietal regions contralateral to the side of the clinical manifestations is characteristic of corticobasal degeneration.