Prolonged cortical silent period is related to poor fitness and fatigue, but not tumor necrosis factor, in Multiple Sclerosis

Publication date: Available online 4 February 2019

Source: Clinical Neurophysiology

Author(s): Arthur R. Chaves, Liam P. Kelly, Craig S. Moore, Mark Stefanelli, Michelle Ploughman

Abstract

Objective

Poor fitness among people with multiple sclerosis (MS) aggravates disease symptoms. Whether low fitness levels accompany brain functioning changes is unknown.

Methods

MS patients (n=82) completed a graded maximal exercise test, blood was drawn, and transcranial magnetic stimulation determined resting and active motor thresholds, motor evoked potential latency, and cortical silent period (CSP).

Results

Sixty-two percent of participants had fitness levels ranked below 10^th percentile. Fitness was not associated with disability measured using the Expanded Disability Status Scale (EDSS). Regression analyses revealed that, cardiorespiratory fitness, when controlling for disease demographics, contributed 23.7% (p < 0.001) to the model explaining variance in CSP. Regression analysis using cardiorespiratory fitness and CSP as predictors showed that CSP alone explained 19.9% of variance in subjective fatigue (p = 0.002). Tumor necrosis factor was not associated with any variable.

Conclusion

Low fitness was associated with longer CSP in MS. Longer CSP was, in turn, related to greater MS fatigue.

Significance

MS patients had extremely low levels of cardiorespiratory fitness. Poor fitness predicted longer CSP, a marker of greater intracortical inhibition, which was linked to MS fatigue. Future research should examine whether aerobic training could shorten CSP and potentially lessen inhibition of cortical networks.

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