Continuous motor unit activity syndromes: a video-polysomnographic study

Objective To ascertain the presence of abnormalities of sleep in patients with continuous motor unit activity with and without symptoms of central nervous system involvement. Methods Five patients with isolated neuromyotonia (Isaacs' syndrome) and 1 patient with Morvan syndrome underwent 24-h videopolysomnographic recording to investigate sleep structure, motor activities and autonomic variables during sleep. Results Macro- and microstructural organization of sleep and of the attending autonomic variables were substantially normal in patients with Isaacs' syndrome. On the contrary, sleep structure was severely disrupted with subcontinuous dream enactment and hallucinations in the patient with Morvan syndrome. The pattern of the neuromyotonic discharges, however, was not different between the patients with Isaacs' syndrome compared to Morvan syndrome, the EMG discharges persisting throughout the 24 h of recording and affecting wakefulness and sleep equally. Conclusions Neuromyotonia is compatible with normal organization of sleep. The severe sleep abnormalities observed in Morvan syndrome cannot be simply attributed to the effects of neuromyotonia of peripheral origin. Significance Even though neuromyotonia is common to both Isaacs' and Morvan syndromes, the two conditions differ significantly in regard to CNS involvement with sleep abnormalities and lumping the two conditions together is not justified on clinical and neurophysiological grounds.