Somatosensory and acoustic brain stem reflex myoclonus.

A patient with brain stem reflex myoclonus due to a massive midbrain infarct was studied electrophysiologically. Myoclonic jerks were elicited at variable latencies by tapping anywhere on the body or by acoustic stimuli, and mainly involved flexor muscles of upper extremities. The existence of convergence of somatosensory and acoustic inputs in the brain stem was suggested. This myoclonus seemed to be mediated by a mechanism similar to the spino-bulbo-spinal reflex.     

A case of postanoxic encephalopathy with cortical action and brainstem reticular reflex myoclonus

A patient with postanoxic encephalopathy, with both action- and stimulus-sensitive reflex myoclonus, is described. The action myoclonus was multifocal and cortical in origin. In contrast, reflex myoclonus elicited by somaesthetic and auditory stimulation was generalised. The earliest reflex electromyograph activity was recorded in the sternocleidomastoid; myoclonic activity then spread up the brainstem and down the spinal cord, suggesting that this reflex myoclonus had its origin in the caudal brainstem. Stimulus sensitivity was greatest in the limbs. The bulbospinal motor pathways involved in the generalised reflex myoclonus were rapidly conducting, and this characteristic distinguishes this form of brainstem reflex myoclonus from that described in hyperekplexia.     

Cortical reflex myoclonus

Three patients with a type of myoclonus produced by intention and somatosensory stimulation were studied with electrophysiologic techniques. Each jerk typically affected only a few contiguous muscles; agonist and antagonist muscles were activated simultaneously with a simple electromyographic (EMG) burst lasting 10 to 30 msec. Cranial nerve muscles were activated in an order indicating that the signal to produce the myoclonus traveled down the brainstem. In action-induced jerks a negative transient in the electroencephalogram (EEG) from the contralateral sensorimotor cortex consistently preceded the jerk with a fixed latency. In reflex-induced jerks this negative transient could be recognized as a component of the sensory evoked potential. The types of myoclonus are reviewed and it is argued that this type of myoclonus is mediated in cerebral cortex and that the negative transient represents a paroxysmal depolarization shift (PDS). The myoclonus may result from hyperactivity of a component of the long-latency stretch reflex.     

Focal reflex myoclonus

In a patient with reflex myoclonus limited to the right side of the body, stimulation of the right median nerve in the index finger or wrist elicited a very large somatosensory evoked response (SER) and a long loop C reflex which represents an electrically evoked myoclonic response. It is suggested that the pathway for the C reflex is through peripheral nerve, dorsal funiculus of spinal cord, contralateral VP nucleus of thalamus, sensorimotor cortex, corticospinal tract, and anterior horn cell. The large SER, C reflex, and myoclonic jerks are presumed to result from a release effect causing increased excitability at central synapses along this pathway. The patient presented has a large atrophic vascular lesion involving the left frontotemporoparietal region and involvement of pathways through the right superior cerebellar peduncle to account for the neural dysfunction.     

Gaze-evoked brainstem myoclonus.

The clinical and electrophysiological aspects of a case where brainstem reticular reflex myoclonus was related to an enlarging pontine lesion are described. It had the unusual characteristic of being evoked by sustained up gaze and left gaze.     

Photic cortical reflex myoclonus

Three patients with flash-evoked myoclonus were studied electrophysiologically. Myoclonic jerks were elicited at a fixed latency after the application of photic stimuli and were always preceded at a fixed time interval by extremely enhanced cortical evoked potentials. The enhanced electroencephalographic (EEG) responses to flash were widely distributed over the scalp and were maximal at the central region; the occipital response preceded the frontocentral response by 3.4 to 5.1 msec. The interval from the frontocentral EEG response to the flash-evoked myoclonus was similar to that from the giant somatosensory evoked potential to the electrically evoked myoclonus. Investigation of recovery of evoked cortical responses and of myoclonic jerks showed a period of extremely enhanced excitability of both central and peripheral phenomena following stimulus. All of these findings suggest a cortical reflex mechanism. The role of the occipital cortex in the pathogenesis of photic cortical reflex myoclonus remains to be elucidated.     

Central diabetes insipidus in hypoxic brain damage

We describe two children who after cardiopulmonary arrest developed hypernatremia at the terminal stage. Urinary antidiuretic hormone concentration was very low, indicating central diabetes insipidus. These cases illustrate the necessity of alertness to the development of central diabetes insipidus in patients with severe hypoxic brain damage.     

Uraemic myoclonus: an example of reticular reflex myoclonus?

Two patients are described who developed action, reflex myoclonus during acute renal failure. In both cases the myoclonus was abolished after the intravenous administration of clonazepam. We suggest that the characteristic action myoclonus, which occurs in both acute renal failure and postanoxic encephalopathy, is caused by a disturbance of function in the lower brainstem reticular formation.     

Focal reflex myoclonus in corticobasal degeneration

Focal reflex myoclonus was observed in a patient clinically diagnosed as affected by corticobasal degeneration. Myoclonus was not preceded by a cortical discharge and contralateral parietal components of the somatosensory evoked potentials were reduced in amplitude. No simple pathophysiological mechanism can account for all cases of focal reflex myoclonus seen in clinical practice.     

Receptors in focal reflex myoclonus.

The findings in a patient with focal reflex or action myoclonus suggest that the cortical somatosensory evoked response and the long loop reflex of the finger flexor muscles evoked by extension of the index finger at the volar surface of the distal phalanx occur largely through stimulation of touch or pressure receptors with evidence of a lesser contribution by joint receptors or muscle stretch receptors. Touch or pressure in the absence of movement is an adequate stimulus, whereas muscle stretch by itself is not.     

Cortical reflex myoclonus in rett syndrome

Rett syndrome (RS) is one of the most frequent causes of mental retardation in females. As there are no known biochemical, genetic, or morphological markers, diagnosis is based on clinical phenotype including severe dementia, autism, truncal ataxia/apraxia, loss of purposeful hand movements, breathing abnormalities, stereotypies, seizures, and extrapyramidal signs. Myoclonus, although reported in some series, has never been characterized. We studied 10 RS patients, age 3 to 20 years, and observed myoclonus in 9. Severity of myoclonus did not correlate with that of the other symptoms or with age. Multifocal, arrhythmic, and asynchronous jerks mainly involved distal limbs. Electromyographic bursts lasted 48 ± 12 msec. Burst-locked electroencephalographic averaging generated a contralateral centroparietal premyclonus transient preceding the burst by 34 ± 7.2 msec. Motor evoked potentials showed normal latencies, indicating integrity of the corticospinal pathway. Somatosensory evoked potentials were enlarged. The C-reflex was hyperexcitable and markedly prolonged (62 ± 4.3 msec), mainly due to increase in cortical relay time (28.4 ± 4.5 msec). We conclude that RS patients show a distinctive pattern of cortical reflex myoclonus with prolonged intracortical delay of the long-loop reflex.     

Reticular reflex myoclonus: a physiological type of human post-hypoxic myoclonus.

A patient with post-hypoxic myoclonus, sensitive to therapy with 5-hydroxytryptophan and clonazepam, was subjected to detailed electrophysiological investigation. Brief generalised jerks followed the critical stimulus of muscle stretch. The electroencephalogram showed generalised spikes that were associated with, but not time locked to, the myoclonus. The cranial nerve nuclei were activated upward. Analysis of the findings suggests that the mechanism of the myoclonus is hyperactivity of a reflex mediated in the reticular formation of the medulla oblongata.     

Central pathway of photic reflex myoclonus.

Direct, new evidence for the cortical origin of photic reflex myoclonus in a patient with "posterior cortical atrophy" is provided. Photic stimulation elicited myoclonic jerks in the right upper limb muscles. An H2(15)O-PET activation study with photic stimulation showed increased regional cerebral blood flow not only in both striate cortices but in the left premotor and primary motor areas as well. Transcranial magnetic stimulation over the area of the left occipital cortex elicited motor evoked potentials in the right upper limb muscles. It is concluded that in the central pathway of photic reflex myoclonus the contralateral occipital cortex is activated first, then the impulses propagate intrahemispherically to the primary motor cortex, to elicit myoclonic jerks.     

Dopamine agonists suppress visual-cortical reflex myoclonus.

Two patients with a diagnosis of olivo-ponto-cerebellar atrophy developed cortical reflex myoclonus to visual (flash) and somaesthetic stimuli. Oral treatment with levodopacarbidopa (1000/100 mg) or subcutaneous administration of apomorphine (1 mg) abolished the visually-triggered myoclonus, without modifying reflex myoclonus to electrical or tactile stimulation. Intravenous administration of lisuride (0.1 mg) produced a marked reduction in both types of reflex myoclonus. These results indicate a selective inhibitory effect of dopamine agonist drugs on visual reflex myoclonus of cortical origin.     

Neuropathology in non-human immunodeficiency virus-infected drug addicts: hypoxic brain damage after chronic intravenous drug abuse

Neuropathological studies were carried out on 180 human immunodeficiency virus-seronegative intravenous drug addicts. The findings in victims of acute heroin intoxication (n = 116) were congestion (99.1%), capillary engorgement (68.1%), and/or perivascular bleeding (68.1%) – hemodynamic processes attributable to toxic primary respiratory failure. In a high percentage of these cases (88%), cerebral edema was also present. In 18 cases of acute heroin intoxication who survived for periods of hours or days, the sole postmortem finding was ischemic nerve cell damage, resembling that typically seen in systemic hypoxia. Semiquantitative analysis revealed nerve cell loss in the hippocampal formation and/ or Purkinje cell layer in 26% of the 162 chronic drug abusers. By contrast, in nearly 80% of these cases, the hippocampus showed enhanced expression of glial fibrillary acid protein by astrocytes and/or a proliferation of microglia, demonstrated by CD68 expression. Since such reactive processes are produced by primary neuronal damage, it can be assumed that chronic intravenous drug abuse results in obviously ischemic nerve cell loss. This could be demonstrated in the hippocampus, but it must also occur throughout the whole brain. The demonstration of ischemic nerve cell damage and neuronal loss or secondary reactive alterations has not been described previously. Received: 31 March 1995 / Revised, accepted: 27 November 1995     

Localized brainstem ischemic damage and Ondine's curse after near-drowning

A 19-year-old man was a victim of near-drowning in fresh water. After he was resuscitated, examination showed nystagmus, absent gag reflex, diminished facial sensation, dysmetria of all limbs, and failure of automatic respiration. His intellect was perfectly preserved. Eight months later, he died suddenly, and the essential neuropathologic findings were limited to the lower brainstem. There was marked neuronal depletion bilaterally in the nucleus gracilis, nucleus cuneatus, nucleus of the tractus solitarius, nucleus ambiguus, and nucleus retroambiguus; several other lower-brainstem nuclei showed evidence of damage, but to lesser extent. The neuropathologic findings seem to have been an unusual consequence of anoxia-ischemia and support previous concepts of the anatomical localization of the human respiratory centers.     

Electrophysiological monitoring of the brainstem function in impending brain death--serial changes of blink reflex and brainstem auditory evoked potential

Serial changes of EEG, BR and BAEP recordings were obtained over a period of two days on two patients who had suffered massive cerebral hemorrhage while their clinical condition evolved from coma with evidence of preserved cerebral and brainstem functions to a state meeting the criteria of brain death. As clinical evidence of deteriorating brainstem function became apparent in case 1, first wave IV and V components of BAEP disappeared while waves I to III were normal. Finally, when clinical criteria of brain death were fulfilled, the BAEP response was restricted to wave I with small amplitude to stimulation of left ear only. These serial changes were likely consistent with gradual dissolution of brainstem function in a rostrocaudal direction. By contrast, in case 2, the BAEP response was restricted to waves I and II and was stationary in the whole process of impending brain death in no association with some preservation of cerebral and brainstem function. The changes of BAEP was not parallel to the progressive deterioration of EEG and BR. After meeting clinical criteria of brain death, complete abolition of waves II and I was sequential in that order, and then Babinski sign besides withdrawal and deep tendon reflexes may revive in the extremities. Monitoring of serial electrophysiological changes is helpful in the course of impending brain death to determine whether revival of Babinski sign is due to recovery of cerebral-brainstem dysfunction or due to establishment of spinal autonomy.