|Beitragstitel||Evaluation of Motor Fatigability in a Facioscapulohumeral Muscular Dystrophy Patient|
INTRODUCTION: In facioscapulohumeral muscular dystrophy (FSHD), the third most common muscular dystrophy, fatigue is a critical and early symptom flag of the pathological processes leading to muscle wasting and to the incurable decline of the subjects' quality of life. Notwithstanding the clinical importance of fatigue in FSHD, the relative contribution of central and peripheral mechanisms to perceived fatigue is currently unknown, neither if it may temporally precede the appearance of detectable alterations in skeletal muscles.
AIM: Aims of the present study were: 1) to examine the myoelectric manifestations of central (FD, fractal dimension) and peripheral (CV, conduction velocity) fatigue of a FSHD patient (Score 1, according to Lamperti et al. 2010); 2) To assess whether myoelectric manifestations of fatigue precede or follow detectable muscle alterations by magnetic resonance imaging (MRI).
METHODS: Surface EMG signals were recorded with linear adhesive arrays in biceps brachii short head during isometric contractions at 20% and 60% of the maximum voluntary contraction (MVC) for 1 min and 20 s respectively at 90 degrees knee joint angle. Initial values and rate of change (slope) of mean frequency of the power spectrum (MNF), CV and FD of the EMG signal were calculated. Total body muscle MRI was also obtained.
RESULTS: MRI revealed, among others, abnormalities on T1-weighted sequences corresponding to marked atrophy and fatty fibrous replacement in trapezius muscle bilaterally. No abnormalities in biceps brachii bilaterally were found. A modification of CV slope was observed at 20% MVC in the right biceps brachii (0.0014 vs 0.0021 %/s) compared to the left, thus suggesting the presence of peripheral fatigability at low force output. This alteration was associated with a higher initial value and positive MNF slope, and equal initial value and unchanged FD slope, suggesting higher muscle fibers recruitment and unchanged central fatigue at low force development. On the contrary, all estimated parameters displayed a significant slope variation at 60% MVC in the right biceps only. No slope changes were observed in the contralateral biceps.
CONCLUSION: These results seem to highlight the arising of central and peripheral myoelectric manifestations of fatigue and a progressive reduction of fibers recruitment at higher force output only in the right muscle. Importantly these changes seem to precede phenotypical alterations detectable by muscle MRI.