Corticospinal output during muscular fatigue differs in multiple sclerosis patients compared to healthy controls

In multiple sclerosis (MS), fatigue is a common and often disabling symptom. It has multiple causes with central motor fatigue playing an important role.

The objective of this study was to analyse the central motor conduction changes in relation to muscle contraction force during muscle fatigue and recovery in MS patients compared to healthy controls.

A total of 23 MS patients with fatigue and 13 healthy subjects were assessed during 2 minutes of fatiguing exercise of the abductor digiti minimi muscle of the hand and the subsequent 7 minutes of recovery. Central motor conduction was quantified by transcranial magnetic stimulation using the triple stimulation protocol and calculating a central conduction index (CCI).

Force declined to 36% of the pre-exercise level (SD 16%; p < 0.01) in MS patients and to 44% (SD 9%, p < 0.01) in healthy subjects (group differences, not statistically significant). The decline of the CCI was significantly less marked in patients (-20%, SD 26%, p < 0.05) than in healthy subjects (-57%, SD 15%, p < 0.05; group differences, p < 0.05). The decline of force and CCI were not correlated in either group.

During a fatiguing exercise, the decline in central motor conduction is significantly less pronounced in MS patients than healthy subjects, although the reduction of force is similar.