Chronic muscle stimulation improves muscle function and reverts the abnormal surface EMG pattern in Myotonic Dystrophy: a pilot study

Carmelo Chisari,Federica Bertolucci,Stefania Dalise,Bruno Rossi

doi:10.1186/1743-0003-10-94

Abstract

BackgroundTo date, in Myotonic Dystrophy type 1 (DM1) the rehabilitative interventions have always been aimed at muscle strengthening, increasing of fatigue resistance and improving of aerobic metabolism efficiency whereas the electrical membrane fault has always been addressed pharmacologically. Neuromuscular electrical stimulation (NMES) is a useful therapeutic tool in sport medicine and in the rehabilitation of many clinical conditions characterized by motor impairment such as stroke, cerebral palsy and spinal cord injury.The aim of our pilot study was to evaluate the effects of chronic electrical stimulation both on functional and electrical properties of muscle in a small group of DM1 patients.MethodsFive DM1 patients and one patient with Congenital Myotonia (CM) performed a home electrical stimulation of the tibialis anterior muscle lasting 15 days with a frequency of two daily sessions of 60 minutes each. Muscle strength was assessed according to the MRC scale (Medical Research Council) and functional tests (10 Meter Walking Test, 6 Minutes Walking Test and Timed Up and Go Test) were performed. We analyzed the average rectified value of sEMG signal amplitude (ARV) to characterize the sarcolemmal excitability.ResultsAfter the treatment an increase of muscle strength in those DM1 patients with a mild strength deficit was observed. In all subjects an improvement of 10MWT was recorded. Five patients improved their performance in the 6MWT. In TUG test 4 out of 6 patients showed a slight reduction in execution time. All patients reported a subjective improvement when walking. A complete recovery of the normal increasing ARV curve was observed in 4 out of 5 DM1 patients; the CM patient didn’t show modification of the ARV pattern.ConclusionsNMES determined a clear-cut improvement of both the muscular weakness and the sarcolemmal excitability alteration in our small group of DM1 patients. Therefore this rehabilitative approach, if confirmed by further extensive studies, could be considered early in the management of muscular impairment in these patients. An attractive hypothesis to explain our encouraging result could be represented by a functional inhibition of SK3 channels expressed in muscle of DM1 subjects.

Highlights

To date, in Myotonic Dystrophy type 1 (DM1) the rehabilitative interventions have always been aimed at muscle strengthening, increasing of fatigue resistance and improving of aerobic metabolism efficiency whereas the electrical membrane fault has always been addressed pharmacologically
The abnormal repeated triplet is situated in a non-coding region of the gene, so it was suggested a loss of function of Myotonic Dystrophy protein kinase (DMPK) protein, caused by either a transcriptional repression or a gain of function mediated by the mutant RNA transcripts
The results of this pilot study show that neuromuscular electrical stimulation (NMES) in patients affected by Myotonic Dystrophy type 1 and Congenital Myotonia determines a clear improvement of muscular impairment

Summary

Introduction

In Myotonic Dystrophy type 1 (DM1) the rehabilitative interventions have always been aimed at muscle strengthening, increasing of fatigue resistance and improving of aerobic metabolism efficiency whereas the electrical membrane fault has always been addressed pharmacologically. Myotonia refers to impaired muscle relaxation following a voluntary forceful contraction. It is found in several clinical disorders with different etiologies. Myotonic dystrophy type 1 (DM1) is the most common form of muscular dystrophy in adults affecting approximately 1 in 8000. It is an autosomal dominant inherited disorder with a peculiar and rare pattern of multisystemic clinical features, affecting skeletal muscles, heart, eyes, endocrine and central nervous systems [1]. The genetic basis consist of an expansion of an unstable (CTG)n triplet repetition on chromosome 19 in the 3’ un-translated region (3’-UTR) of the gene encoding for myotonic dystrophy protein kinase (DMPK). The best theory explaining the pathogenesis focuses on RNA transcripts: in DM1 cells were found multiple nuclear foci of mutant DMPK-RNA, containing pathogenic CUG repeats, which could produce defects in alternative splicing of multiple RNAs, providing a basis for the multisystemic features of DM1 [2]

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