Accuracy in the clinical diagnosis of parkinsonian syndromes.

This review of Parkinson's disease and related disorders emphasizes the difficulties of distinguishing between variants of the parkinsonian syndrome. Characteristic clinical features may remain absent for many months, but accuracy of diagnosis may be improved by considering certain presenting symptoms and signs. The main characteristics of various parkinsonian syndromes are reviewed and their major distinguishing features are emphasized. Future improvement in the precision of clinical diagnosis, especially early in the course of parkinsonian syndromes, will depend on selecting out patients with Parkinson's disease using positive diagnostic criteria.