INVESTIGATIONS ON A PATIENT SUBJECT TO MYOCLONIC SEIZURES AFTER SENSORY STIMULATION

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Abstract
A detailed case is reported of a patient who suffered from myoclonic seizures which could be elicted by sensory stimulation. The patient exhibited major convulsions and during the last 5 months of his 2 1/2 yr. observation developed a spastic paresis of the left arm and hand with contracture. The etiology of the condition remains obscure. The EEG between seizures showed an 8 to 10 per sec. rhythm in the parieto-occipital region and some low voltage 4 to 7 per sec. bilaterally. There was no significant change in overbreathing for 3 min. During the myoclonic seizures multiple spikes of 30 to 50 mil. sec. duration and 50 to 150 microvolt amplitude were seen. They were always larger on the left than on the right side. Simultaneous electromyograms showed muscle activity larger on the right than on the left and beginning in the thigh 80 to 120 m. sec. after the beginning of the cerebral disturbance. When the myoclonic seizure was produced by a peripheral stimulus, either a tendon tap or electrical stimulation of a peripheral nerve, the electrical response recorded from the scalp consists of 2 parts. The early response consists of 2 deflections positive in sign at the electrode near the central sulcus compared to a frontal electrode, followed by negative deflectives of approx. 100 m. sec. duration on which are superimposed rhythmic spikes of 30 m. sec. duration. If the stimuli were repeated at intervals of 1 sec. or less, all portions of the cerebral response and the myoclonic burst were absent except the initial double positive deflection which was unaffected. Following the demonstration of these facts, the remainder of the paper consists of an analysis of this initial constant deflection following stimulation of various nerves of both upper and lower extremities at varying strength of stimuli and at varying intervals between shocks. The following conclusions were drawn from these expts. The first part of the potential change is largest on the side of the head opposite to the site of the stimulous and 3 cm. in front of the surface marking of the central sulcus. It is maximal near to the midline when stimulating the leg, and 6-8 cm. lateral to it when stimulating the arm. The latency of the response on the scalp becomes greater when the stimulus is applied nearer to the periphery; it varies from 19 m. sec. stimulating at the elbow to 43 m. sec. when the stimulus is applied at the ankle. The response to the second of 2 stimuli is depressed if the 2d stimulus is applied within 30 m. sec. of the 1st. The response is facilitated if the interval between the stimuli is from 60 to 100 m. sec, and has recovered almost completely at 300-350 m. sec. The findings are compared with those in healthy subjects. The responses to stimulation in the subject with myoclonus have a similar latency, form and time course to those in healthy subjects but they are between 5 and 10 times as large. The significance of the findings is discussed.
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