THE CAUSES OF EPILEPSY: ANOXIA

Anoxia means lack of sufficient oxygen, an essential component of the normal ongoing chemistry of the cell. Cerebral nerve cells are amongst the highest consumers of oxygen in the body, as reflected in the fact that a quarter of all arterial blood goes to the brain. If the oxygen supply is cut off, then damage to nerve cells occurs after a few minutes. Some die, but others are damaged in such a way that they may paroxysm ally discharge in subsequent life.

Anoxia may occur at birth. During each uterine contraction in a prolonged labour the fetal heart rate slows, and the supply of oxygenated blood to the brain is reduced. The umbilical cord may become tightly wound around the baby’s neck. The placenta may separate prematurely. After birth, for a variety of reasons, the child may not breathe for a few minutes. These are four examples of how anoxic brain damage can occur at birth. If severe, the brain damage results in severe learning difficulties, cerebral palsy, or epilepsy. However, as has already been mentioned, the cause of these three is often due to antenatal factors rather than problems with the birth itself.

Anoxia also occurs in febrile convulsions, as has already been discussed. During a seizure the oxygen requirements of brain nerve cells are enormously increased, and yet the resulting convulsion interferes with normal respiration, so that the blood leaving the lungs picks up insufficient oxygen. The combination of excessive demand and inadequate supply may on rare occasions result in anoxic damage to cerebral nerve cells. The nerve cells which seem most susceptible to damage, at the age at which febrile convulsions occur, are in the temporal lobe.

A stroke is usually due to an obstruction to an arterial vessel to one particular part of the brain, so nerve cells in the territory supplied by the blocked vessel either die as a result of lack of oxygen, or become damaged in such a way that they may form a focus for paroxysmal discharges later. Most strokes occur in late adult life, and cerebrovascular disease accounts for much of the epilepsy beginning in old age. Occasionally, however, a stroke may occur in a young adult or even in a child.

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