Sign Up for a Free Account
  • Updated 03.01.2023
  • Released 11.16.2004
  • Expires For CME 03.01.2026

Reflex anoxic seizures



Reflex anoxic seizures are a common type of nonepileptic seizure mainly encountered in infants and younger children but occasionally persisting into adulthood. They are dramatic and frightening to witness but in nearly all cases benign and without sequelae. They are often confused with other forms of syncope. Exceptionally, they may trigger epileptic seizures. This phenomenon has been reported in adults as well as in children. In this article, the author reviews their clinical manifestations, discusses their differential diagnosis (concentrating on the need to consider rare but potentially fatal conditions that may mimic reflex anoxic seizures, such as long QT syndromes), and considers the latest approaches to management.

Key points

• Reflex anoxic seizures are a form of syncope usually starting in infancy or early childhood.

• They are precipitated by noxious stimuli, which can be physical or emotional.

• For reasons yet unknown, the noxious stimulus causes a vagally mediated brief asystole, which is responsible for the syncope.

• The clinical manifestations are dominated by the child losing awareness and falling to the ground, appearing a deathly white color. Convulsive features are common.

• Reflex anoxic seizures are benign in the sense that sufferers always recover from them. If they are very frequent, cardiac pacing can be helpful.

• Reflex anoxic epileptic seizures may occur with pathogenic variants, such as SCN1B or SCN8, but the neurodevelopment is abnormal in these cases.

Historical note and terminology

Reflex anoxic seizures are a form of syncope encountered mainly, but not exclusively, in young children. A seizure is, in the broadest sense of the word, any clinical event caused by a transient (but not necessarily short-lived) alteration of cerebral function. When the seizure is epileptic, it is caused by an epileptic mechanism, ie, as a consequence of excessive or hypersynchronous discharge of cortical neurons. By definition, “syncope” is from the Greek, “a cutting off,” implying an abrupt interruption in the supply of energy to the cerebral cortex. This is usually a consequence of a reduction in cerebral perfusion by oxygenated blood. It can be a result of either a sudden reduction in the blood flow to the brain, a drop in the oxygen content of the blood supplying the brain, or a combination of the two. It follows that syncope can be a consequence of numerous different pathophysiological mechanisms but that they are nonepileptic because they do not arise as a consequence of excessive or hypersynchronous discharge of cortical neurons. Moreover, syncope can have different clinical manifestations, ranging from transient loss of consciousness, usually accompanied by a decrease or loss in postural tone (the principal manifestations of “simple faints”), to tonic and myoclonic events and nonepileptic spasms.

To avoid confusion, it is perhaps best to consider the terms “anoxic seizure” and “syncope” as being synonymous and meaning clinical events caused by transient alterations in cerebral function arising as a consequence of sudden reductions in cerebral perfusion of oxygenated blood. Numerous types of anoxic seizure or syncope have been described. The best known, if not necessarily the best understood, is the “simple faint” or vasovagal syncope. At least in infants and children, breath-holding attacks and reflex anoxic seizures are also widely recognized and common causes of anoxic seizures or syncope. Other types include vagovagal syncope, cardiac syncope (including long QT disorders, other cardiac arrhythmias, and structural cardiac disease), syncope due to orthostasis, hyperventilation, compulsive Valsalva maneuvers, gastroesophageal reflux, and imposed upper airway obstruction (suffocation). In addition, anoxic seizures or syncope are a feature of both hyperekplexia and familial rectal pain syndrome. Finally, there are likely to be other types of anoxic seizure or syncope not yet characterized.

Reflex anoxic seizures are a particular type of anoxic seizure or syncope, most commonly seen in young children in whom an anoxic seizure or syncope is provoked or precipitated by a noxious stimulus (hence, “reflex”). Various precipitants have been identified, but the most common is an unexpected bump to the head. Breath-holding attacks have been recognized for centuries. However, it is only relatively recently that their pathophysiology has begun to be understood, and in consequence, their separation from reflex anoxic seizures has been recognized. Indeed, the distinction between the two may not be complete.

Stephenson reviewed the historical development of the concept of breath-holding attacks and reflex anoxic seizures and the separation of the two (37). Key developments were:

(1) Clear description by Bridge and colleagues of the typical features of mild breath-holding spells (03).

(2) Description of the clinical and EEG features of anoxic convulsions in children by Gastaut and Gastaut (09).

(3) Anoxic anoxia proposed as the mechanism of breath-holding spells by Gauk and colleagues (10).

(4) Description by Maulsby and Kellaway of the clinical features during more severe attacks, including the occurrence of a convulsive phase (20).

(5) Separation by Maulsby and Kellaway of anoxic seizures into two types: Type I, corresponding to (blue) breath-holding spells, and type II (hypoxic crises) (20).

(6) Confirmation by Lombroso and Lerman that two distinct types of breath-holding spells could be distinguished (18). These authors preferred the terms cyanotic breath-holding and pallid infantile syncope. However, they also demonstrated that both types of attack could occur in the same child.

(7) The term “reflex anoxic seizure” proposed by Stephenson for the type II spells of Maulsby and Kellaway and the pallid infantile syncope of Lombroso and Lerman (33). This term has now been widely adopted.

(8) Recognition that true epileptic seizures can exceptionally follow reflex anoxic seizures in children (anoxic-epileptic seizures) and in adults (36; 37; 13).

(9) Reflex anoxic seizures may occur with de novo pathogenic SCN8A variants, but the neurodevelopment is abnormal in these cases (26).

It is now generally recognized that breath-holding attacks and reflex anoxic seizures represent distinct pathophysiological phenomena, which, nevertheless, can occur in the same subject. It has become clear that prolonged respiratory apnea is a principle, if not the only, mechanism responsible for breath-holding spells in which cyanosis is a major feature and that brief cardiac asystole as a consequence of excess activity of the vagus nerve is the cause of reflex anoxic seizures. This may also be the case with de novo pathogenic SCN8A variants (26).

This is an article preview.
Start a Free Account
to access the full version.

  • Nearly 3,000 illustrations, including video clips of neurologic disorders.

  • Every article is reviewed by our esteemed Editorial Board for accuracy and currency.

  • Full spectrum of neurology in 1,200 comprehensive articles.

  • Listen to MedLink on the go with Audio versions of each article.

Questions or Comment?

MedLink®, LLC

3525 Del Mar Heights Rd, Ste 304
San Diego, CA 92130-2122

Toll Free (U.S. + Canada): 800-452-2400

US Number: +1-619-640-4660



ISSN: 2831-9125