The heterogeneity of Parkinson's disease: clinical and prognostic implications.

In 334 patients with idiopathic Parkinson's disease, deterioration in mental status paralleled severity of bradykinesia, postural instability, and gait difficulty. Tremor was relatively independent of the other cardinal signs and was associated with relative preservation of mental status, earlier age at onset, family history of parkinsonism, and more favorable prognosis. There seem to be at least two Parkinson's subgroups: one with postural instability and gait difficulty and another with tremor as the dominant feature.