[Pseudo-myasthenic syndromes. Clinical and electromyographic review of 4 cases, one with an unusual reaction to lidocaine (author's transl)].

The authors report 4 cases of pseudo-myasthenic syndrome followed with EMG for a period varying from a few months to 4 years. They go over the electrophysiological points which led to the diagnosis: small amplitude of the muscle potential evoked by simple shock and, in particular, the phenomenon of potentiation which may reach 2000 p. 100 during repetitive stimulation at high frequencies. Study of the behaviour of the muscle potential during ischaemia, which was carried out twice, showed an absence of fatigue of the potential which may be considered a sign of disturbance at the muscle level of the motor-end plate. On the other hand, EMG signs of peripheral neuropathy, which were found 3 times, rather suggests a motor neuropathy responsible for the presynaptic block. In 3 patients guanidine had a beneficial effect and no signs of paraneoplastic aetiology had occurred yet. The fourth case, with a bronchial neoplasm discovered at autopsy, was clearly improved by injectable lidocaine, for which no explanation can be supplied.