Periodic synchronous and stereotyped myoclonus with postanoxic coma.

5 patients with cerebral anoxia of various etiology had postanoxic coma with the syndrome of periodic synchronous and sterotyped myoclonus first mentioned by Lance and Adams. These authors observed action myoclonus as a sequel to this syndrome which is rarely survived. Most reports have dealt mainly with its bad prognostic significance. Although the localization of action myoclonus has much been discussed, and is still controversial, little attention has been paid to the possible localizing significance of its acute precursor syndrome. Most patients with this type of myoclonus (all in our series) present a lower pontine/upper oblongata syndrome. The distribution patterns of the jerks are constant, do not represent topographic but functional relationships showing innervation patterns which are presumably integrated in the vestibular system and upper oblongata reticular formation. Interval histograms show that the jerks, unlike those in subacute sclerosing panencephalitis, are not repeated at regular intervals. Several rhythms might be intermingled, or a rhythmic (physiological?) pacemaker could be modified by proprioception of the jerks. The latter possibility is supported by the observation that EEG discharges in one patient became rhythmic when the jerks ceased. The only other instance of rhythmicity was in a very special observation of continuous seesaw alternations of slow jerks of m. levator palpebrae sup., and tonic contractions of m. corrugator glabellae. Rhythmicity in this case had a 1:2 relation to heart rate indicating the nucleus tractus solitarii region as a possible site of origin of the impulses. Our observations indicate an upper oblongata origin for this type of myoclonus. Autopsies in 3 of our cases revealed widespread severe anoxic damage but nothing to add to the pathological localization.