[Myoclonia. From the myoclonia of Papio papio to various human myoclonias]

Abstract

The baboon Papio papio is naturally predisposed to present several types of myoclonus, the study of which can help in understanding the various human myoclonic symptomatologies. The three types of myoclonus which are studied have been called A, B and C. Myoclonus A, which is induced by intermittent photic stimulation in photosensitive animals, is of epileptic nature: It is always preceded by spikes-waves predominating in the fronto-rolandic cortex (areas 4 and 6) and can be followed by secondarily generalized tonic-clonic seizures. Myoclonus B, which occurs when the animal is agitated, is facilitated by somatic stimulations. Since it is never preceded or accompanied by spikes-waves and since it is never associated with epileptic seizures, myoclonus B is considered as non-epileptic. Myoclonus C occurs during wave-sleep. They are associated with spikes-waves during the slow but not during paradoxical sleep. Myoclonus A, B and C can co-exist in the same animal when it is photosensitive. Myoclonus B and C can co-exist in the same animal when it is non-photosensitive. Clinically, the three types of myoclonus have different symptomatologies. Myoclonus A is bilateral and synchronous. It always involves initially the eyelids and face. It can secondarily become generalized to the whole body. Myoclonus B, which is also bilateral and synchronous, is limited to the truncular musculature and to the proximal part of limbs. It never involves the eyelids and face. It never becomes generalized. Myoclonus C has a variable symptomatology and can be parcellar. The nervous structures originating the three types of myoclonus in the baboon are not identical. Myoclonus A is originated in the fronto-rolandic cortex, where a neuronal generator is triggered by visual inputs induced by photic stimulation. It appears mainly due to a dysfunction of the GABA system, because it is suppressed by GABA agonists and by benzodiazepines. On the contrary, it is facilitated by GABA antagonists. Myoclonus B has probably its origin in the lower brain stem (ponto-bulbar reticular formation) and is favored by cerebellar lesions. It appears mainly due to a dysfunction of the cholinergic system and is considerably facilitated by atropine. Myoclonus C can also have its origin in the lower brain stem but, contrary to myoclonus B, it can involve the cortex and thus can be accompanied by spikes-waves. The 3 types of myoclonus which are distinguished in the baboon have different relationships with epilepsy.(ABSTRACT TRUNCATED AT 250 WORDS)