Computerized posturography analysis of progressive supranuclear palsy: A case-control comparison with Parkinson's disease and healthy controls

Background: Progressive supranuclear palsy (PSP) is a neurodegenerative disorder that is frequently mistaken for Parkinson's disease (PD) in its early stages. Objective: To compare balance measures using computerized posturography in patients with early PSP and early PD. Methods: We performed computerized posturography (SMART Balance Master; NeuroCom International, Inc, Clackamas, Ore) in 20 patients with clinically diagnosed mild to moderate PSP (ambulatory) and compared results with those from 20 patients with PD of similar age and disease duration who were not receiving medications, and from 20 healthy age- and sex-matched controls. Sensory organization testing (SOT), limits of stability (LOS), and toes-up perturbations (4°at 50°per second) were tested while receiving and not receiving a combination of oral carbidopa (25 mg) and levodopa (250 mg) in the PSP group. Clinical assessment included Unified Parkinson's Disease Rating Scale, Performance-oriented assessments, and functional reach. Results: When compared with the PD and control groups, total LOS time (P<.001) and path sway (P<.001) were significantly prolonged in PSP. Total SOT showed significantly worse scores in PSP compared with PD and control groups (F_2,57=29.6; P<.001). Univariate follow-up tests comparing PSP and PD showed differences in the following conditions: eyes open and visual sway (P=.003), eyes open and platform sway (P=.003), eyes closed and platform sway (P<.001), and eyes open and platform and visual sway (P<.001). Medium- and long-latency responses to perturbation were similar, but a larger number in the PSP group lacked short-latency responses (χ²= 11.3; P=.002). Levodopa administration did not significantly improve any aspect of posturography testing in PSP. In differentiating PSP from PD, LOS time and SOT condition of eyes open and platform and visual sway were nearly 100% sensitive and 100% specific (canonical correlation, 0.91). Conclusions: Computerized posturography testing reliably differentiated early PSP from early PD and age-matched controls. The PSP group demonstrated severely contracted limits of stability with probable deficits in motor programming. Results of SOT in PSP suggested a vestibular pattern and overreliance on visual cues, even when incorrect. The absence of short-latency responses (monosynaptic reflex arch) suggests an additional disturbance in the spinal cord or peripheral nervous system.