Dec
09
2009

THE FIRST SEIZURE AND THE DIAGNOSIS OF EPILEPSY: OTHER CAUSES OF IMPAIRED OXYGEN SUPPLY TO THE BRAIN-LOCALIZED REDUCTION IN CEREBRAL BLOOD FLOW

The changes in blood flow that we have considered so far affect all parts of the brain equally. In older people, arteriosclerotic changes take place in the arteries in the neck and head. There may be a temporary blockage of an artery to one part of the brain by a fragment of chalky deposit or thrombus swept downstream from a larger artery by the flow of blood. Neurologists call these blockages ‘transient ischaemic attacks’. In some of these short episodes, muscle weakness or tingling in one or other limb may slightly resemble partial motor or sensory seizures. However, although focal motor seizures may arise in the scarred brain in the territory of a permanently blocked artery after a stroke, transient ischaemic attacks are associated with transient paralysis rather than convulsions.

In younger people, localized (focal) neurological phenomena occur in migraine. In the first stage of a classical migraine attack, arterial spasm occurs, reducing cerebral blood flow focally. It is unclear whether this is primary or secondary to some depression of nerve cell activity. The occipital area is the region most often affected. This results in a hallucination of distorted vision or flashing lights, rather than the formed visual hallucination which may be part of a partial seizure arising in a temporal lob. Occassionally spasm affects the motor or sensory areas of the brain, producing short-lived paralysis or disturbance of sensation, without convulsions, on the opposite side of the body.

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