Inverse associations between cerebellar inhibition and motor impairment in spinocerebellar ataxia type 3

• Published in: Brain stimulation Vol. 14; no. 2; pp. 351 - 357
• Main Authors: Maas, Roderick P.P.W.M., van de Warrenburg, Bart P.C., Schutter, Dennis J.L.G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-03-2021; Elsevier
• Subjects: Cerebellar inhibition; Cerebellothalamocortical tract; Scale for the Assessment and Rating of Ataxia; Spinocerebellar ataxia type 3; TMS; Scale for the Assessment and Rating of Ataxia; Spinocerebellar ataxia type 3; TMS; Cerebellar inhibition; Cerebellothalamocortical tract
• ISSN: 1935-861X; 1876-4754
• DOI: 10.1016/j.brs.2021.01.020

Cerebellar ataxia generally results from a lesion disrupting the corticopontocerebellar or cerebellothalamocortical tract. The cerebellar inhibition (CBI) paradigm represents a dual-coil transcranial magnetic stimulation protocol that interrogates the integrity of the latter pathway. Whether CBI has clinical relevance in ataxia patients remains largely unknown because associations with pertinent disease severity measures in etiologically homogeneous cohorts have not been previously examined.
To investigate if CBI correlates with clinical and functional indices of disease severity in individuals with spinocerebellar ataxia type 3 (SCA3).
CBI was assessed in fourteen SCA3 patients by paired-pulse cerebellar-motor cortex (M1) stimulation using interstimulus intervals of 3, 5, and 10 ms. Correlation coefficients were determined between CBI and ataxia severity, manual dexterity, and walking speed.
Suppression of M1 excitability occurred 5 ms following a contralateral cerebellar conditioning stimulus in SCA3 patients, but, on average, CBI was significantly reduced as compared to a healthy control group from the literature (p < 0.001). A significant association was found between decreased CBI levels and higher Scale for the Assessment and Rating of Ataxia (SARA) scores (r = −0.62, p = 0.019). CBI was negatively correlated with axial, appendicular, and speech subscores, as well as with nine-hole peg test performance (r = −0.69, p = 0.006). No association was observed between CBI and walking speed. As expected, there were no significant clinical-neurophysiological correlations at 3 and 10 ms interstimulus intervals.
Our results provide the first neurophysiological evidence for an inverse association between cerebellothalamocortical tract integrity, as reflected by reduced levels of CBI, and ataxia severity in SCA3 patients. Longitudinal studies are required to evaluate if CBI could serve as a marker of disease progression.
•Decreased levels of cerebellar inhibition in SCA3 patients were associated with more severe ataxia.•Clinical-neurophysiological associations were specific to the 5 ms interstimulus interval.•The lack of correlation with cognitive performance underscores the motor specificity of CBI.