**1. Introduction**

Muscular dystrophy (MD) is characterized by an absence or disruption of dystrophin and associated proteins with a severe pathology of the skeletal musculature with severe motor disabilities and even premature death of the individual. These proteins do not only have an important function within the skeletal musculature but also within the central nervous system. Thus, patients with muscular dystrophies often suffer from cognitive impairment, learning disability, and variable degrees of mental retardation in addition to progressive muscular weakness [1–3]. Patients with facioscapulohumeral muscular dystrophy (FSHD) are often affected by epilepsy [4, 5]. However, the pathogenetic role played by the absence or disruption of dystrophin on CNS function has not been clarified so far.

Transcranial magnetic stimulation (TMS) is a proper method to assess brain cortical excitability that is disturbed in muscular dystrophies. A TMS assessment of brain cortical function in DMD patients has yielded contradictory results [6]. While Yayla et al. reported no CNS abnormalities and similar motor threshold (MT) values in DMD patients and healthy controls, Di Lazzaro et al. reported a higher MT for magnetic than for electrical stimulation in four DMD patients [7]. Methodological reasons, as well as the small sample size of the latter study, may account for the discrepancies. Because repetitive TMS (rTMS) modulates cortical excitability, possibly by inducing a short-term increase in synaptic efficacy [8], rTMS can be used to investigate motor cortex excitability in humans. Changes in the size and threshold of motor evoked potentials (MEPs) and cortical silent period (CSP) duration evoked by rTMS delivered in 5 Hz trains of stimuli at suprathreshold intensity have been tested by Golaszewski et al. [9]. The main finding of this study was that 5 Hz-rTMS delivered in trains failed to elicit the normal MEP facilitation over the train in a group of Becker Muscular Dystrophy (BMD) patients with mental retardation or borderline mental retardation and BMD patients with normal intelligence and healthy controls did not show any abnormalities in 5 Hz-rTMS MEPs and CSPs. The lack of MEP facilitation in mentally retarded or borderline BMD patients during the 5 Hz-rTMS train of stimuli may thus reflect an altered short-term synaptic enhancement.

With the means of transcranial magnetic stimulation, important neurophysiologic and pathophysiologic aspects of cortical involvement in myopathies can be detected [10, 11]. So far, a few studies applying TMS have detected abnormalities in cortical reactivity and plasticity in MD patients.
