Somatosensory evoked potential recovery in myotonic dystrophy

Objective: To evaluate recovery functions of the sensory cortex using somatosensory evoked potentials (SEPs) elicited by paired stimuli of the median nerve in patients with myotonic dystrophy (MD). Subjects/methods: Twelve MD patients were enrolled in the present investigation. Five patients with facioscapulohumeral muscular dystrophy (FSH) and 12 healthy volunteers were studied as control groups. SEP was recorded from the hand sensory area contralateral to the median nerve stimulated at the wrist. Single pulse or paired-pulse stimuli at various interstimulus intervals (ISIs) (10, 20, 40, 60, 80, 100, 150, 200 and 300 ms) were given. Recovery functions of N9, N20onset-N20peak, N20–P25 and P25–N33 components were studied. Results: Conventional SEPs to a single stimulus were normal in the latency and amplitude in all the patients. Recovery functions of both N9 and N20o–N20p components were normal in the patients. In contrast, in MD patients, disinhibited or hyperexcitable recovery pattern was observed in recovery curves of the N20–P25 or P25–N33 components, whereas those were normal in FSH patients. Conclusions: Disinhibited cortical excitability (or hyperexcitability) is present in the sensory cortex in patients with myotonic dystrophy. This may reflect cortical pathology or functional alteration of the sensory cortex in MD.