Health News

Three interlocking circles, the area of which is roughly proportional to the frequency of occurrence of various types of seizure. The central circle incorporates tonic-clonic (grand mal) seizures. The left-hand circle contains partial seizures, many of which become secondarily generalized, as indicated by the considerable overlap between the two circles. Most partial seizures arise from some focal area of structural abnormality within the brain. These seizures can be said to be symptomatic of some underlying problem—so-called symptomatic epilepsy.

The right-hand circle indicates typical absences (petit mal seizures). About 30 per cent of children with petit mal also have grand mal seizures, as is indicated by the overlap between right hand and centre circles. Such primary generalized epilepsy is not symptomatic of underlying structural brain disease, and may be said to be constitutional or idiopathic epilepsy.

The area of the centre circle that is not overlapped by the left and right hand circles contains those subjects who only have tonic-clonic (grand mal) seizures. Such cryptogenic epilepsy (epilepsy of hidden cause), less common since the advent of sophisticated investigations, should not be called idiopathic. Two possibilities exist—either the petit mal trait was not obvious in childhood, and grand mal seizures are the only manifestation of idiopathic epilepsy, or the seizure discharge from a small lesion becomes generalized so quickly that its initial partial phase is overlooked. It is often difficult to distinguish between the two possibilities even with prolonged EEG recording, unless a seizure actually occurs during the record.

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