Objective: We assessed R2 Blink Reflex Recovery Cycle (R2 BRRC) in drug-naive Parkinson’s disease (PD) patients with unilateral tremor and/or rigidity, diagnosed as hemiparkinson syndrome, to evaluate differences in brainstem excitability between affected and unaffected sides.

Background: R2 BRRC is a neurophysiological tool, used to measure brainstem excitability and it is known to be enhanced in PD [1]. Previous studies were conducted on Blink Reflex (BR) in early hemiparkinson patients [2]. However, to our knowledge, there are no studies on R2BRRC in drug-naive patients with hemiparkinson syndrome.

Method: We prospectively enrolled 18 drug-naive PD patients: 7 patients with right hemiparkinson syndrome and 11 patient with left hemiparkinson syndrome. We investigated BR and R2BRRC at interstimulus intervals (ISIs) of 100, 150, 200, 300, 400, 500 and 750 ms bilaterally.

Results: All PD patients showed an early recruitment of R2BRRC. Right hemiparkinson patients showed a significant enhanced recruitment in left R2BRRC at ISI of 150 ms (p<0.05), whereas left hemiparkinson patients showed a significant early recruitment in right R2BRRC at ISIs of 100, 150 and 200 ms (p<0.027; p<0.006; p<0.007). Our findings showed a contralateral increase of brainstem excitability to the clinically affected side in drug-naive PD patients.

Conclusion: R2BRRC is a helpful neurophysiological tool to understand pathophysiological mechanisms underneath PD. We hypothesized that an increased state of neurons excitability probably due to a predominant contralateral dysfunction of basal ganglia structures could explain the asymmetric brainstem disinhibition observed in hemiparkinson patients.

References: 1. Kimura J. Disorder of interneurons in Parkinsonism. The orbicularis oculi reflex to paired stimuli. Brain 1973; 96: 87-96. 2. Dengler R, Kossev A, Struppler A. Unilateral reduction of the early and late blink reflex component in hemiparkinson syndrome. Electroencephalogr Clin Neurophysiol 1982; 54: 689-98.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/unilateral-increase-of-blink-reflex-recovery-cycle-in-drug-naive-hemiparkinson-syndrome/