Gastaut (10) used the term reflex anoxic cerebral seizures to describe all the various syncopes, sobbing spasms, and breath-holding spells that followed noxious stimuli in young children. Since 1978, reflex anoxic seizure has been used more specifically to describe a particular type of nonepileptic convulsive event, most commonly induced in young children by an unexpected bump to the head (11). Although other terminology, such as pallid breath-holding and pallid infantile syncope, have been applied to such episodes (12), the term reflex anoxic seizure is now widely recognized (13,14).
Until the advent of cardiac loop recorders, direct evidence with respect to the pathophysiology of natural attacks had been very limited. Since prolonged cardiac recording has become feasible in children, many recordings of prolonged reflex asystole have been recorded and several examples published (15-18).
An extract from a letter written to a pediatrician by a consultant neurologist may give the reader some idea of the diagnostic difficulties that were commonly experienced before the phenomenon of reflex asystole was well known. He wrote:
Case study #1. Thank you for asking me to see this 7-year-old young man. As a toddler he began to have attacks of loss of awareness, rigidity, and eye rolling which would be induced by minor knocks. This has continued and recently an episode occurred in which he had an undoubted tonic-clonic seizure with incontinence of urine. Curiously, as far as I can tell from mother's account, every attack has been triggered by a minor bump on the head, and he has never had an attack out of the blue. He had difficulties at birth. The family history is clear except for a convulsion in the mother when she was tiny, about which there is no further information. It seems to me that this boy is having a form of reflex epileptic seizure, and my inclination would have been to start treatment with sodium valproate. In fact mother told me ... that he was started on Epilim just a couple of weeks ago. Even though two EEGs have been normal, I do not doubt that he has an epileptic tendency, and I am sure that he should be on treatment for at least a couple of years free from attacks.
When this boy was seen in a further consultation he was "an epileptic," his school knew about his "epilepsy," his mother was in touch with an epilepsy association, and invalidity benefit had been applied for on the basis of epilepsy. Presumably, the difficulty here was that neither the pediatrician nor the neurologist knew that this was precisely the story of nonepileptic reflex anoxic seizures of vagally mediated cardioinhibitory type, otherwise known as reflex asystolic syncope. It is probable that the diagnosis of breath-holding spells had been entertained earlier, but quite rightly discarded, if only because the boy was by now over the age of 7 years. The alternative diagnosis of a primary cardiac syncope, such as is seen in the long QT syndrome (see Long QT Disorders below)— LQT—was not considered, perhaps because syncopes in LQT had not at that time been described exclusively as a sequel to minor bumps to the head. Since then, there has been a report of one case of LQT in which four or five syncopes, the last fatal, were precipitated by a blow to the head (19: page 94).
As children grow older, reflex anoxic seizures may cease altogether or change to more obvious convulsive or nonconvulsive vasovagal syncope in childhood and adolescence. It is possible, although proper long-term studies have not been done, that syncopes may reappear in old age.
Beyond the toddler stage, children may report sensory disturbances along with the syncopes. Most dramatic are out-of-body experiences with a dreamlike quality (17), which may include the child feeling as if he or she has floated up to the ceiling and is watching his or her body lying on the floor in a seizure (20). Night terrors (see Parasomnias below) as a sequel to the syn-copal episodes have also been reported by parents.
It is often said that breath-holding spells (see Breath-holding Attacks below) or syncope caused by prolonged expiratory apnea may also occur in children who have reflex anoxic seizures. It is certainly true that in some children some episodes may be more blue or cyan-otic and some more pale and blanched looking, but there are no good recordings that confirm this proposition.
It is best to try to make a precise diagnosis as to whether a convulsive syncope in a young child is cardio-genic or respiratory in origin. If it is cardiogenic, then the main differential diagnosis is a reflex anoxic seizure (reflex asystolic syncope) versus a convulsive syncope from long QT syndrome or other cardiac cause. If it appears to be a respiratory (i.e. apneic) syncope, then the differential diagnosis is breath-holding spells (prolonged end-expiratory apnea) or suffocation (in particular, from imposed upper-airway obstruction as part of Meadow's syndrome (see Suffocation below).
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