Objective: The objective of this study was to investigate the association between glabellar tap findings with nigrostriatal dopamine function in patients with unclear parkinsonism.

Background: Striatal DAT deficiency is a hallmark of neurodegenerative parkinsonism syndromes. Diagnostics of these syndromes is currently mainly based on clinical characteristics. Brain presynaptic dopamine imaging can be used to differentiate unclear cases by evaluating striatal dopamine deficit. However, imaging is not always available, and it is associated with costs and ionizing radiation. Testing primitive reflexes, such as glabellar tap test, can be helpful in differential diagnostics but the value of these tests and their association with brain dopamine deficit are not well characterized. The purpose of this study was to investigate the association between glabellar tap findings with nigrostriatal dopamine function in patients with unclear parkinsonism.

Method: In this cross-sectional study, we performed glabellar tap on 327 patients with unclear parkinsonism immediately prior to diagnostic dopamine transporter (DAT) [I-123] FP-CIT SPECT imaging. Specific putamen DAT binding was used to measure presynaptic nigrostriatal dopamine function. Putamen binding was compared between patients with abnormal (>3 taps before habituation) and normal (max. 3 taps) glabellar tap reflex using the two-sample t-test. Furthermore, putamen binding was correlated with glabellar tap results using Pearson’s correlation coefficient.

Results: Putamen DAT binding was lower in the abnormal compared to normal glabellar tap group [mean (SD) 2.04 (0.81) vs. 2.54 (0.79), p<0.001]. The result remained highly significant when controlled for age and gender (p=0.001). In addition, there was a negative correlation between DAT binding and glabellar tap score (r=-0.30, p<0.001), which again remained significant after adjusting for age and gender (r=-0.30, p<0.001).

Conclusion: Abnormal glabellar tap reflex is associated with lower levels of presynaptic striatal DAT binding in patients with unclear parkinsonism. This finding suggests that glabellar tap could be a useful clinical test for differential diagnostics in this population and possibly reduce the need for molecular brain imaging.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/glabellar-tap-predicts-dopamine-transporter-deficiency-in-parkinsonism/