Motor excitability in myopathy

Objective: To explore whether patients with myopathy present changes in motoneuronal excitability. Methods: Patients with well-defined myopathies were studied with single and paired pulse transcranial magnetic stimulations and electrical nerve stimulations to explore neuronal motor excitability. Motor-evoked potentials were recorded from the clinically unaffected first dorsal interosseous muscle (n=10) and the paretic deltoid muscle (n=8). Results: Compared to an age-matched healthy control group, myopathic patients showed a reduction of intracortical inhibition, enhancements of α-motoneuron excitability and increased amplitudes of motor-evoked potentials during target muscle contraction. These alterations were present in clinically affected and clinically unaffected muscles. Conclusion: In myopathy, nervous system excitability may be altered, presenting as a motor disinhibition on cortical and subcortical levels.