Differential diagnosis of PSP.

The clinical diagnosis of PSP depends primarily on the history and the physical findings. Clinicians should be alerted to the possibility of this condition in assessing patients presenting with atypical parkinsonism and other complex extrapyramidal syndromes in late middle age or later. The differential diagnosis includes MSA (both OPCA and SND), PD, CBD and cerebrovascular disease. PD is probably the most common erroneous diagnosis. Unfortunately, pathognomonic signs do not usually appear until several years, after symptom onset. No specific laboratory test is yet available. Neuroimaging studies show characteristic anatomic alterations only late in the course of the illness and must be correlated with the clinical findings.