Value of the E.E.G. in Diagnosis of Epilepsy
Authors: D. Hill
Journal: BMJ (1958)

Focal or Partial Epilepsies The E.E.G. has taught us a great deal about these forms of epilepsy.Deductions on the site of origin based on clinical observation were confirmed and methods of spread over the cortex have been studied, but there are two ways in which we have gained original knowledge-the recognition of foci of discharge in the so-called silent areas of the frontal and temporal lobes, and the bilateral occurrence of so many focal discharges.We used to believe that major fits were of two kinds-those with a generalized onset and those with a focal onset.It is now evident that when a major fit begins with, say, twitching or tingling of a limb, what in fact has happened is that a focal fit has initiated a general- ized convulsion-there have been two attacks, the focal fit having initiated the major fit much as electrical stimulation might.This fact, which is so evident in electroencephalographic records, was really evident from observation of the attacks too, because a major fit always has the tonic phase first, the clonus being caused by interruption of tonus, while a clonic focal fit consists of much more rapid jerks of part of the body, and the march of events is clonus, tonus, and then clonus-obviously two different kinds of fit succeeding each other.Another fundamental fact that must be recognized to achieve a logical understanding of focal fits is this: that, however elaborate may be the movements or feelings in an epileptic attack in which consciousness is preserved, they are always due to focal disturbance of brain function.The only difference between an attack with a primitive muscle twitch and one with co-ordinated, apparently purposive dis- order of social behaviour, is that the first is caused by dis- turbance of function in the relatively primitive motor cortex, and the second in a more highly elaborated integrative part of the cortex.Those attacks we most readily think of as " focal "-the clonus of a limb, local tingling or numbness, flashing light, a smell, a buzzing sound, and so on-all happen in the first cell station of reception of sensations into the brain or the last cell station of emergence of move- ment.They are simple phenomena, which were therefore understood early in the study of epilepsy.The "psychic fits" or psychomotor attacks, the elaborate hallucinations, dreamy states, emotional experiences, or visceral disorders of epilepsy are all just as truly caused by focal discharge in the brain as the experimental surgery of Penfield and others has demonstrated.That being so, focal fits can be classified according to their clinical pattern-motor, sensory, psychic, and so on-or upon the basis of their known origin.The second is probably the more useful, because, as the list of epileptic events shown above indicates, there are too many forms of epileptic experience to make their division a profit- able one.A classification based on the part of the brain first affected, with a statement of the clinical events, is acceptable in all countries.Focal fits may be cortical or subcortical, but much of the cortex, like that of the island of Reil and the undersuirface of the temporal lobe, is buried.Cortical discharges may occur in primitive areas or as.so- ciation areas, or may spread from one to the other.They may, as so often in the temporal lobe, be bilateral and they may march over the cortex in a Jacksonian way.We now recognize that that Jacksonian march may include very complex experiences in which division into physical and psychological becomes meaningless.