Diagnostic potential of saccadometry in progressive supranuclear palsy

Background: Progressive supranuclear palsy (PSP), an atypical parkinsonian syndrome characterized by extrapyramidal features, imbalance, supranuclear gaze paresis and dementia, can be difficult to diagnose, especially in the early stages. From the clinician's point of view, the main difficulty with this disorder is the inability to provide an accurate diagnosis, at least for the initial stages of the disease, where symptoms are often confused with other parkinsonian disorders. This inability complicates the recruitment of patients with early-stage parkinsonism to trials of disease-modifying therapy. Objectives: To determine whether quantitative, objective examination of saccadic latency distributions can help to distinguish PSP patients from other groups of parkinsonian patients. Materials & methods: We used a newly developed portable saccadometer to compare saccadic latency distributions of a group of PSP patients with two other groups in whom the initial differential diagnosis included PSP: one of these groups had Parkinson's disease and the other had developed a range of parkinsonian conditions (multiple system atrophy, dementia with Lewy bodies and corticobasal degeneration). Results: The use of a combination of saccadic parameters provided a greater discriminative power than the use of only one parameter, such as median latency. Statistical analysis and parameterization of the distributions robustly distinguished the three groups. Conclusions: This approach appears to have considerable diagnostic potential in allowing a more accurate diagnosis of PSP, and may help particularly to eliminate misdiagnosis with other parkinsonian conditions.