Objective: We developed a videographic tool to quantitatively assess the Glabellar Reflex (GR) in healthy patients for further analysis in Parkinson (PD) patients.

Background: The Glabellar Tap Sign is a clinical sign in Parkinson (PD) patients indicating a disinhibition of the pyramidal tracts. While healthy controls blink only once when taped on the forehead (glabellar reflex), PD patients do not habituate to this stimulus and blink repeatedly. While this clinical finding is widely accepted by neurologists in clinical practice, reliable tools to quantify this sign are not available.

Method: We assessed the GR of 12 healthy controls with two different methods. In the first setup, the tap stimulus was applied by a vibration device with fixed frequency and intensity. The blinking frequency was extracted by processing a recorded video. In the second setup, a hammer connected to the electrodiagnostic system (Natus Nicolet EDX) was used for stimulus application. Here, blinking frequency was determined via electromyography derived from small electrodes applied to the skin of the orbital muscle. We recorded the number of blinks and the time to habituation. To model pathologic habituation, our subjects blinked continuously.

Results: With our setup we could analyze the GR in a standardized manner by either a conventional electrodiagnostic system or our novel vibration-video-analysis system. Habituation as modeled by forced blinking could be detected and analyzed in an automated fashion using image processing.

Conclusion: We developed a quantitative tool to assess the GR in healthy volunteers. We plan a study in PD patients to establish cut-offs of the Glabellar Tap Sign and to evaluate the specificity of this sign in other neurodegenerative disorders.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-videographic-tool-for-quantitative-assessment-of-the-glabellar-reflex/