T H E I N C I D E N C E OF F O C A L A N D N O N - F O C A L EEG A B N O R M A L I T I E S I N C L I N I C A L EPILEPSY

JOHN KtaSHMaN, M.D., JuLlo VkSQUEZ, M.D. and SYDNrY GOLSTEIN 2

The most important contribution made by electroencephalography to clinical medicine has been to increase our understanding of the epilepsies. The initial impetus in this direction was the classical work of Gibbs, Gibbs and Lennox (1937, 1938), who demonstrated the characteristic brain wave patterns that occurred during certain types of clinical seizures.

In the clinical study of epileptic patients, it is exceptional to obtain an EEG record during a seizure; and m o r e and more, we have come to depend on the nature of the interseizure ab- normalities in the evaluation of each patient's problem.

The analysis of many thousands of inter- seizure records of epileptic patients has led us to the conclusion that it is seldom possible to predict accurately from the form of the EEG discharges alone what type of clinical attack will occur. On the other hand, what does seem to be important in such a correlation, is the cerebral localization of the pathological EEG activity (Jasper and Kershman 1941). This realization has brought increasing emphasis in attempts to localize the EEG disturbances. Initial efforts in this direction resulted in uncovering of a surprisingly high proportion of localized EEG foci in epileptic patients.

The present report is an analysis of the clinical data and EEG records of a series of patients with epilepsy from a number of dif- ferent medical centres across Canada. It con- firms the fact that nearly half of the patients have a detectable cortical focus in the EEG. Various other correlations have also been studied.

*Read at the Eastern EEG Association Meeting, March 4, 1950.

2 From the Queen Mary Veterans' Hospital, Depart- ment of Veterans" Affairs, Montreal, The Montreal Neurological Institute and the Department of Neurology and Neurosurgery, McGill University. Montreal.

MATERIAL AND METHODS

Immediately after World War II, the Can- adian Department of Veterans' Affairs, organ- ized the establishment of a series of EEG units in the larger population centres across Canada, namely Vancquver, Edmonton, Winnipeg, Lon- don, Toronto, Montreal and Halifax. Except for Toronto and Montreal, when these labora- tories started to function, they were the only EEG units in the area and because of this, through the generosity of the Department of Veterans' Affairs, the facilities were made avail- able to the general public. Since then, a large number of civilian patients have been exam- ined and we have accumulated the data on a group of unselected civilian patients with epilepsy referred for EEG by their family physicians or consultants. The findings will be reported below.

Veterans and patients from the armed serv- ices with epilepsy will also be described.

All the records in each of the sevcn units have been taken in the same way. A standard 4-channel Grass EEG machine was used in centres, a 6-channel machine in one and a 4- channel electrophysical apparatus in another centre. The method of examination was essen- tially the same as that used at the Montreal Neurological Institute (Jasper, Kershman and Elvidge 1940). If a focal EEG abnormality was revealed by the usual examination or suspected from the clinical data, extra electrode place- ments were used if necessary, and careful local- izing studies were done.

The techniques and criteria for localization (Jasper and Kershman 1941, Jaspe r 1941, Aird and Adams 1950) included a study of amplitude differences, hypersynchrony, wave form, rec- ordings from serially arranged electrodes, phase reversals, etc. Hyperventilation was carried out routinely for 3 min. and if a *'break" occurred in the record, the patient was usually given a glass of sweetened orange juice and hyper-

15

16 J O H N KERSHMAN, JULIO VASQUEZ and SYDNEY GOLDSTEIN

ventilation repeated in 30 min. In many in- stances, hydration (Penfield and Erickson 1941) or Metrazol (Cure, Rasmussen and Jasper 1948) was used to excite an inactive abnormality or to improve the localization, if it was obscure.

In every instance, the EEG record was first interpreted by the local physician in charge of the laboratory and then sent for consultation to the Queen Mary Veterans' Hospital in Montreal which was the supervisory centre. Any disagreement in interpretation was fully discussed and in many patients, the EEG exam- ination was repeated for confirmation or elabo- ration.

The diagnosis and classification of the type of EEG abnormality was based on the records taken between seizures. Seizure records were seldom obtained and are rarely necessary for diagnostic purposes.

The EEG abnormality was classified as "focal, clear", if there was a single area beneath or near one electrode from which spikes, sharp waves or high voltage rhythms and slow waves were recorded. If this was accompanied by some dysrhythmia elsewhere or there was a bilateral discharge (usually in the temporal regions) with one side predominant, the record was considered "focal, complicated". EEG dis- orders of the "bilaterally synchronous" and "diffuse" types are sufficiently clear to need no further elaboration (Jasper and Kershman 1941, Jasper 1941).

cluded al though in some patients with epilepsy who were included, a tumor may subsequently have been found.

It should be noted that not all the cor- relating data was available in every patient studied. The totals shown in each table indicate the number of patients in whom the particular data under discussion was reliably and accurately obtained.

RESULTS

Before presenting the findings for these new groups of patients, it is of interest to summarize the previous results. Table I shows the distribution of various types of EEG abnormalities reported by Jasper and Kershman (1941) in their first classification study. Forty- seven per cent of a group of 494 patients had a focal EEG abnormality, 33 per cent had bi- laterally synchronous discharges, 15 per cent had diffuse abnormality and 5 per cent had a normal record. In a subsequent analysis of a different group of 1289 patients (Jasper and Kershman 1944) the results, as indicated in table I, were almost identical.

Table II, group 1, shows the incidence in the present study of the various types of EEG abnormality seen in 428 civilian patients with clinical epilepsy, ranging in age from less than one to over seventy years. No Montreal patients or veterans are included in these figures.

There were 38 per cent with focal abnormal- ities. This is about 8-9 per cent less than m

"['ABLE I

D I S T R I B U T I O N OF TYPES OF EEG ABNORMALITIES IN PREVIOt 'S GROUPS OF EPILEPTIC PATIENTS.

FOEa]

No. %

232 47

589 46

Bflaterall) Synchronou.~

No. 7~

163 33

422 32

D#iu , e

No. %

7~ 15

i89 14.5

NorIlla]

No. %

Total No. . f Patient L

26 5 4 9 4 '

89 7.0 1289

Jasper and Kershman ( 1941 ). 2 Jasper and Kershman (1944) .

It should be emphasized that the only criterion for the inclusion of any patient in this study was a clear diagnosis of clinical epilepsy. For example, patients with brain tumors known to exist at the time of examination were ex-

the previous reports and may be due to the exclusion of veterans and soldiers - - a group of young and middle aged men who are most likely to have post-traumatic and other types of focal lesions.

EEG ABNORMALITIES IN CLINICAL EPILEPSY 17

The cases f rom the Queen Mary Veterans ' Hospi ta l in Mont rea l consisted of veterans and service pat ients only. As shown in table II, g roup 2, of 262 pat ients studied, 55 per cent had a clear focal abnormal i ty and another 11.5 per cent had a focal complicated EEG abnormal- ity, mak ing a total of 66.5 per cent with focal EEG records. This indicates how high the propor t ion of focal abnormali t ies can be in a g roup conta in ing a large number of male pa- tients with war injuries. Many service cases and veterans with severe intracranial injuries and post- t raumatic epi lepsy were seen first in

them, the medical p roblem was less severe than those s tudied in Mont rea l and attacks were less frequent. The percentage dis t r ibut ion of the various types of EEG abnormali t ies was quite similar to the civilian group in table II and the patients shown in table I. There is one im- por tant difference h o w e v e r : the 16 per cent with normal EEG records is much h igher than in any of other groups. This is due to the fact that these pat ients with inf requent seizures had relatively inactive foci and less f requent EEG abnormali ty . At tempts to activate EEG ab- normali t ies with hydra t ion and Metrazol were

TABLE II

Type o/ Patient

Group 1. civilian

2. veterans Montreal

3. veterans non-Mtl.

" ' 4 . t o t a l veterans

Focal Clear

No. %

Focal Compl.

No. %

Normal

No. % Total

i ,

117 27.5 46 10.5 10 428

144 55 30 11.5 7.5 262

45 25.5 25 14 16 175

55 12.5

101 11.5

189 43.5

Total Focal Bilaterally Synchronous

No. % No. %

163 38 133 31

174 66.5 49 18.5

58 39.5 50 29

244 56.0 99 22.5

- - i 4O7 47 232 27

m various new groups of epileptic patients.

Di[]use

No. %

89 21 43

19 7.5 20

27 15.5 28

46 10.5 48

i i135 15.5 91 r

studied.

"' 5. grand total 306 35.5

11 437

10.5 I

J Distribution of types of EEG abnormality Group 4 is the total of groups 2 and 3. Group 5 is the grand total of all the new patients

865

the Mont rea l hospi tal after their re turn from overseas and usually many of the most severe problems were eventual ly sent to Mont rea l for study and decision on surgical and medical therapy. This group represents therefore an un- usually selected group of patients but by no means all of them were post- t raumatic epilepsy. There were among them many pat ients who developed seizures f rom other causes and vet- erans who had been discharged f rom the services because of many di f ferent kinds of epilepsy. These make up most of the cases with bi lateral ly synchronous EEG abnormali t ies (18.5 per cent) and diffuse abnormali t ies (7.5 per cent) .

Table II, g roup 3 shows a g roup of veterans and service patients with epilepsy all s tudied in centres other than Montreal . In most of

carried out much less commonly in other centres than in the Queen Mary Veterans ' Hospi ta l in Montreal .

If all the veteran and service patients are added together ( table II, g roup 4) a total of 56 per cent had a focal EEG abnormali ty .

Combin ing all the civilians and veterans gives a total of 865 patients with clinical epilep- sy from across Canada. As shown in table II, g roup 5, the total incidence of focal EEG ab- normal i ty was 47 per cent, a f igure pract ical ly identical with the groups repor ted in table I. Bilaterally synchronous EEG abnormali t ies were sl ightly fewer (27 per cent as against 33 per cent) and diffuse abnormali t ies (15.5 per cent) were the same. The percentage of normal rec- ords (10.5 per cent) was s l ight ly h igher d i i e f ly

18 J O H N KERSHMAN, JULIO VASQUEZ and S Y D N E Y G O L D S T E I N

because in the patients studied in Montreal, more persistent efforts were made with activat- ing agents and repeated examinations to pre- cipitate EEG disturbances. Other factors will be discussed later.

TABLE III

26,18 PATIENTS W I T H EPILEPSY

Total of all Groups

EEG Abnormality No. %

Focal ............................................... 1228 46.5

Bilaterally Synchronous ............... 817 31

Ditfuse ........................................... 397 15.0

Normal ........................................... 206 7.5

Total ............................................ 2648 100

One of us (J. K.) has been associated with both the earlier reports and the present studies. This comprises a grand total of 2648 patients with clinical epilepsy whose EEG records have been carefully reviewed and interpreted by at least two and often more co-workers. In most of them, a detailed analysis of the seizure pat- terns and the case history was correlated with the EEG.

The distribution of the various types of EEG abnormality in these 2648 patients is shown in table III. It indicates that 46.5 per cent had a

focal EEG abnormality, 31 per cent had bilater- ally synchronous discharges and 15 per cent had diffuse EEG changes, while 7.5 per cent had a normal record.

Relation between Clinical Seizure and Type of EEG Abnormality

A personal interview was possible or suffi- ciently detailed accounts of the clinical seizure were available in 1668 patients out of the ,total 2648 shown in table III so that there was ade- quate information to classify correctly the clinical type of seizure.

The seizure patterns were divided into three main groups :

(a) Grand real (non-focal, major attacks be- ginning with loss of consciousness and generalized movements).

(b) Petit mal or petit mal with grand real.

(c) Focal seizures (minor, major or both).

Patients with psychomotor attacks or ictal automatisms were considered to have focal seizures (from the temporal regions and vicin- ity) as is consistent with most of the available evidence (Jasper and Kershman 1941, Gibbs, Gibbs and Fuster 1948, MacLean and Arellano 1950).

The gross percentage distribution of the various types of clinical seizures and their cor- relation with EEG abnormalities is shown in table IV.

There were 712 patients with focal seizures and 81 per cent had a focal EEG abnormality.

TABLE IV

RELATION BETWEEN EEG A N D TYPE OF CLINICAL SEIZURE

EEG Abnormality

Fo ca 1

Bilaterally Synchronous

Diffuse

Total

I Petit Mal Grand Mal [P.M. °&rG.M.

No. % No. % t

208 28

307 44

194 28

709 100

I

Focal

No. %

i 37 15 576 8t i

196 80 82 11

I 14 5 ] 54 8

Total

821

585

262

1668 247 100 712 100 i

EEG ABNORMALITIES IN CLINICAL EPILEPSY 19

This figure is only slightly less than the 87 per cent correlation reported by Gibbs, Merritt and Gibbs (1943) and 90.7 per cent by O'Leary and Fields (1949) and a little higher than the 75 per cent reported by Echlin (1943) and all these other reports were based on a much smaller series of cases.

There were 1! per cent of the patients with focal seizures who had bilaterally synchronous EEG abnormalities. Most of them had 4-6/sec. waves in the temporal regions and it was im- possible to decide which was the predominantly abnormal side. This is not an unusual phenom- enon even in proven unilateral temporal lobe lesions especially if deepseated or subcortical. Only 8 per cent had diffuse EEG abnormality. Whether this was primary or secondary to re- peated attacks is not known and it is possible that in some instances, the focal character of the clinical seizure may have been a misinterpreta- tion.

Of the 247 patients who had petit mal, either alone or combined with grand mal, 80 per cent had bilaterally synchronous EEG abnormalities. This type of EEG disturbance is therefore just as characteristic for patients with petit real as is the focal EEG abnormality for those with focal seizures.

However, it is important to note that not all patients with bilaterally synchronous EEG abnormality had petit real attacks. Of the 585 patients with bilaterally synchronous EEG changes (table IV) only 33 per cent had petit real as shown in table V, while 53 per cent had grand mal seizures without petit real (table V).

The type of EEG disturbance in patients who had grand real seizures alone was much less characteristic than it was in patients with focal epilepsy or petit mal; 44 per cent had bilaterally synchr9nous EEG abnormality (table IV) while 28 per cent were focal and 28 per cent diffuse. It may be that among the 28 per cent with focal EEG abnormality, there were instances in which the focal nature of the seizure had not been clinically recognized, in some perhaps because the attack began with loss of consciousness. Penfield and Kristiansen (1948) have shown that initial unconsciousness may occur in focal epilepsy, but it is an uncer- tain localizing sign.

TABLE V RELATION BETWEEN TYPE OF EEG

ABNORMALITY AND CLINICAL SEIZURE (Per cent of - - 1668 Patients)

Petit Mal EEG Grand or

Abnormality Mal P.M. & G.M. Focal Total

Focal 25 5 70 100

Bilaterally Synchronous 53 33 14 100

Diffuse 74 5 21 100

It is of interest that if all the 262 patients with diffuse EEG abnormality are considered as a group, by far the greatest number of them (74 per cent) had grand real seizures only. This is shown in table V.

N o r m a l Records in Epi lept ic Patients

There has been considerable interest in this problem. The most recent and detailed study is that made by Abbott and Schwab (1948) who pointed out that in patients with a normal rec- ord there was later onset, fewer different kinds of spells, less frequent spells, greater response to medicine, etc. Our own statistics indicate that the percentage of normal records varies from

TABLE VI THE iNCIDENCE OF NORMAL EEG'S IN VARIOUS

TYPES OF CLINICAL SEIZURES ( 1289 Patients)

Petit Mal Grand or

Mal P.M. & G.M. Focal Total % % % %

Abnormal EEG 89.5 97.5 96.0 93.0

Borderline Normal 2.0 0.5 1.0 1.5

Normal EEG 8.5 2.0 3.0 5.5

No. of Patients 602 195 492 1289

5 to 16 per cent in various groups (table II) the overall average for 2648 patients being 7.5 per cent (table I I I ) . In Montreal, where at-

20 JOHN KERSHMAN, JULIO VASQUEZ and SYDNEY GOLDSTEIN

tempts were made more often to activate ab- normal i ty and more careful surveys were done in the focal cases, the percentage of normal records was consistently lower than in other EEG centres. Table VI shows that the type of seizures is also impor tant . Pat ients with grand mal had the highest percentage (10.5 per cent) of border l ine and normal records; the lowest occurred in patients with peti t mal where only 2.5 per cent had border l ine or normal records. In 492 pat ients with focal seizures, only 4.0 per cent had border i ine or normal EEGs and 96 per cent were abnormal.

There is also a relat ion to the age of the patient at the t ime of the examinat ion and to the age of onset of seizures as will be discussed below.

below the age of 25 years and decline very rapidly after 56 years. Diffuse EEG disturbances are more evenly dis t r ibuted but are commonest in ch i ldhood and fewest after 56 years.

The lowest incidence of normal records oc- curs dur ing chi ldhood and adolescence (5 - - 6.5 per cent). Af ter the age of 56, it is about four times higher (20.5 per cent).

If the age at the time of onset of seizures is s tudied in relation to the EEG abnormali t ies, certain characteristics stand out quite clearly as is shown in table VIII .

Focal EEG abnormal i ty increases sharply from 36 to 54 per cent if the attacks begin after the age of 25 years and is 75 per cent if attacks begin after the age of 56 years. The incidence of post- traumatic, degenerat ive and

TABLE VII RELATION BETWEEN EEG ABNORMALITY AND AGE AT TIME OF EXAMINATION

(2176 Patients)

EEG Abnormality Age : 0-8 9-16 17-24 25-40 41-55 56 on Total

% % % % go go go

Focal ...................................................... 32 40 35,5 51 50.5

Bilaterally Synchronous ........................ 41 34.5 38,5 26 17

Diffuse .................................................. 22 19 14 13 17

Normal .................................................. 5 6.5 12 10 15.5

Total .................................................. 100 100 100 100 100

No. of Patients .................................... 235 387 502 692 259

60.5 44

7 30

12 16

20.5 I0

100 I oo

101 2176

Relation between Age and EEG Abnormalily

Table VII shows the relation between the age at the t ime of examinat ion and the various types of EEG abnormal i ty and the occurrence of normal records. Borderl ine abnormali t ies are included here in the normal group.

It is apparent from table VII that the per- centage of focal EEG abnormali t ies increases sharply in patients over 25 years of age and is 60 per cent in those over 56 years. This is most likely due to the occurrence of traumatic lesions and par t icular ly of degenerat ive lesions in older patients. On the other hand, bi lateral ly synchronous EEG abnormali t ies are commonest

neoplastic diseases probably accounts for this. Yet even when attacks begin before the age of 8 years, 43 per cent have focal abnormali ty. Birth t rauma and post-infectious cerebral com- plications are the likeliest causes.

The incidence of bi lateral ly synchronous EEG abnormal i ty declines sharply from 35 to 13.5 per cent in patients whose attacks begin after the age of 25 year~. It is down to 4 per cent when attacks begin after 56 years of age. By far the greatest number of bi lateral ly syn- chronous disturbances consists of 3/see. wave and spike pat terns and 3/see. rhythmic waves. Their p redominant occurrence in patients whose

EEG ABNORMALITIES IN CLINICAL EPILEPSY

TABLE VIII

RELATION BETWEEN AGE OF ONSET OF SEIZURES AND EEG ABNORMALITY ( 1235 Patients)

21

EEG Abnormality Age: 0-8 9-16 17-24 25-40 41-55 56 on Total % % % % % % %

Focal ...................................................... 43 38 36 54 50 75 43.5

Bilaterally Synchronous ........................ 37 38 35 13.5 13 4 30

Diffuse .................................................. 17.5 15 13 14.5 17 7 15

Borderline Normal .............................. 1 1 1 3 l 4 1.5

Normal .................................................. 2.5 8 15 15 19 10 10

Total .................................................. 100 I00 100 100 100 100 100

No. of Patients .................................... 340 325 228 230 84 28 1235

attacks begin at the younger age levels em- phasizes their relationship to idiopathic or cryptogenic epilepsy.

Diffuse EEG changes are distributed quite evenly (13 - - 17 per cent) regardless of the age of onset of seizures but there is a sudden decline after the age of 56.

The lowest percentage of borderl ine and normal EEG records (3.5 per cent) is seen in patients whose attacks begin before the age of 8 years. The next lowest (9 per cent) occurs in the next age group (9-16 years) and then the figures do not change greatly (16 - - 20 per cent) if the attacks begin between 17 and 55 years of age, with a slight drop thereafter.

C O M M E N T S

Focal epilepsy is much more frequent than is generally supposed. Clinically, its differen- t iation from other convulsive disorders depends on the meticulous care with which informat ion is elicited from the patient, his relatives, friends and other witnesses about the aura and onset of the attack. This informat ion must then be correlated with an intimate and accurate knowl- edge of the physiology of various parts of the cerebral cortex and subcortical regions. In this connection, the contr ibutions of Penfield and his co-workers (Penfield and Erickson 1941,

Penfield and Kristiansen 1948) are of inestim- able value.

The recognition of focal electroencephal- ographic abnormalities similarly depends to a large extent on the methods used for their detection and the care exercised in doing local- ization studies. Certain methods of electrode placements and electrode linkages dur ing record- ings are much more likely to uncover a focal discharge than others.

Recognition of the various abnormal wave forms occurring dur ing various types of clinic- al seizures was an extremely important landmark in the development of our knowledge of the correlation between EEG and clinical epilepsy but the character of the wave forms dur ing an

t This statement has been fully elaborated in a pre- vious report (Kershman 194-/) at the first Annual Meeting of the American Society of Electroencephal- ography. Briefly, it was demonstrated that a minimal adequate examination should include the use of elec- trodes in measured standard positions in the anterior frontal, frontal, central, temporal, parietal and occipital regions with independent ungrounded ear electrodes, recording both bipolar and scalp to ear records from each of these placements, comparing symmetrical tracings from both sides of the head. The use of linked ear electrodes complicates and confuses the interpretation of the records, grounding them partly corrects this but such records are less discriminatory for localizing focal ab- normalities than simple scalp to ear records and bipolar (scalp to scalp) records. The ear electrode is not really an "indifferent" electrode but records activity from in and around the temporal region.

22 JOHN KERSHMAN, JULIO VASQUEZ and SYDNEY GOLDSTEIN

attack has only a limited value in helping to decide the origin of the seizure discharge, just as the generalized movements during the height of the clinical seizure provides no clue to the site of the initial onset. Clinically, the aura and onset are the determining factors. Electrogra- phically, the localization of the interseizure abnormalities provides the clearest indication of the area from which the discharge and the seizure originates.

The demonstration of abnormal wave forms in the EEG record is only the first step; efforts to localize the origin of the discharge are at least as important and much more rewarding in providing an understanding of the clinical nature of the seizure and in learning more about the physiology of the brain.

Methods for localization have been under- going continual refinement. Examples of this are the studies of Aird and Zealear (1949), and AiM and Adams (1950) who emphasized the im- portance of even minor asymmetries and potential differences, the introduction of the nasopharyn- geal electrode (Grinker 1938) subsequently modified by Schwab and by MacLean (1949), the use of bilateral nasopharyngeal electrodes (Arellano and MacLean 1949) and tympanic electrodes (Arellano 1949). Measures which vail activate latent abnormality and make it available for localization studies are o;/ great importance in recognizing loci and in this connection, the use of Metrazol (Kaufman, Marshall and Walker 1947, Cure, Rasmussen and Jasper 1948) seconal, (Gibbs and Gibbs 1949) photic stimulation (Gastaut and co- workers 1949) and auditory stimulation (Gastaut and co-workers 1949, Arellano 1950) are im- portant contributions.

In this study, it has been shown that in 2648 patients with clinica~ epilepsy, intersei- zure abnormalities were p'resent or could be easily precipitated in 92.5 per cent. By appro- priate methods, these abnormalities could be localized to a single unilateral cortical region in 46.5 per cent. There were some differences in the various groups but even in civilian patients excluding veterans, there were 38 per cent with focal EEG discharges. If only veteran groups were studied and careful examinations done, the percentage of focal EEG abnormalities went as high as 66.5 per cent. This figure

closely approximates what Gibbs, Wegner and Gibbs (1944) found in patients with post- traumatic epilepsy.

Obviously, the percentage of focal EEG abnormalities will vary from one group to another, depending on the type of patients that predominate but the surprising finding was that for all the 865 new patients from across Canada reported here, the percentage with localized EEG findings was essentially the same (47 per cent) as occurred in the previous groups studied at the Montreal Neurological Institute.

Table VII indicates that the cases studied included an adequate distribution of every age level and with every kind of seizure (table IV). Considering the large number and variety of patients in these groups, it must be concluded that focal abnormalities make up the largest single group of EEG disturbances found in clinical epilepsy. Certain modifications of this statement might be made for some age groups Reference to table VII indicates that in patients examined between the age of birth and 8 years, there are slightly more bilaterally synchronous disturbances (41 per cent) than focal abnormali- ties (32 per cent) and the percentage is also slightly higher in patients between 17 an~t 24 years of age, but after the age of 25, focal abnor- realities are grossly predominant. If we consider the age of onset of seizures, there are about an equal proportion of bilaterally synchronous and focal abnormalities in p~tients whose attacks begin between 9 and 24 years of age (table VIII ) but in all other groups, there are more focal disturbances, particularly in those whose attacks begin after the age of 25 years.

It should be pointed out that very few of these patients were in chronic institutions and this may make a difference. However, out of 1668 patients (table IV), 709 or 43 per cent had grand mal seizures only and an equal num- ber were clinically focal. Even among the former, 28 per cent had a focal EEG abnormal- ity but in patients with clinically focal seizures, the figure was very much higher (81 per cent). Frequently, electrodes were placed in special locations at or near the site of cerebral injury and this was no doubt a factor in increasing the percentage of localized abnormal records as also was the use of Metrazol and other measures.

We have no hesitation in using the clinical data as a guide to EEG localization studies. The

EEG ABNORMALITIES IN*CLINICAL EPILEPSY 23

value of the EEG record is greatly enhanced when it is done with a full knowledge and understanding of the clinical history. The EEG interpretation is much more meaningful if it is related to all the available clinical information. Only in this way can electroencephalography make its fullest contribution to our understand- ing of the individual patient and add to our general knowledge of cerebral physiology and pathology.

It is interesting that bilaterally synchronous abnormalities, particularly of the 3/sec. type are just as frequent in patients with petit real epilepsy (80 per cent) as are localized EEG disturbances in patients with focal epilepsy. But, when bilaterally synchronous 3/sec. waves occur, it cannot always be assumed that it is due to idiopathic epilepsy. Several instances have been recorded in which abnormality of this type or very closely resembling it, has been caused by a proven cerebral cicatrix (Penfield and Jasper 1947, Jasper and Kershman 1949).

Nor may it be assumed, as so often is the case, that this bilaterally synchronous type of activity is always an indication of clinical petit mal epilepsy. As shown by table V, slightly more than 50 per cent of patients With this kind of discharge have only grand mal seizures. This emphasizes again, the importance of inter- preting the EEG findings in relation with the clinical data.

These s~udies indicate that borderline and normal records are most frequent in patients with grand mal attacks only and least in patients with petit real. The sensitivity of the latter group to hyperventilation and Metrazol is probably one of the reasons for this. It may be that with other methods of activation, this percentage will become smaller for the grand real group also but the age of the patient and the age of onset of seizures are also factors which determine the proportion of normal records. It is obvious that these are much more common in older patients.

SUMMARY AND CONCLUSIONS 1. A group of patients with clinical epilepsy

have been studied in various centres across Canada.

2. In 428 civilian patients, 38 per cent had focal EEG abnormalities.

3. In 262 veterans and service patients who were carefully studied, 66.5 per cent had focal EEG abnormalities.

4. In another group of 175 veterans, 39.5 per cent had focal EEG abnormalities.

5. In the total series of 865 patients, 47 per cent had focal EEG abnormalities.

6. This figure was identical with the per- centage of focal EEG abnormalities found in 2 previous groups of patients studied at the Montreal Neurological Institute.

7. In a total of 2648 patients with clinical epilepsy, focal EEG abnormalities were the largest single group o f E E G disturbances.

8. The percentage of focal disturbances un- covered depends to a considerable extent on the technique and care used in doing localization studies.

9. Eighty-one per cent of patients with clin- ically focal seizures had a focal EEG abnor- mality.

10. Although 80 per cent of patients with petit mal attacks had bilaterally synchronous EEG disturbances, the latter also occurred in 53 per cent of patients who had grand real at- tacks only. This form of discharge therefore, although commonly seen in petit mal, is by no means pathognomonic. Nor is it only seen in idiopathic epilepsy, ~ though they are very fre- quently associated.

11. Diffuse dysrhythmias were most fre- quently associated with patients who had only grand real seizures.

12. Bilaterally synchronous disturbances were much more common in patients whose seizures began before the age of 25 years.

13. Focal EEG abnormalities were much more common in patients over 25 years of age and particularly if the attacks began after the age of 25 years.

14. Diffuse dysrhythmias were evenly dis- tributed in all age groups.

15. Borderline or normal EEG records were seen more frequently in patients with grand mal attacks only and in older patients particu- larly after the age of 56 years.

16. The lowest percentage of normal and borderline records were seen in patients With petit mal and in infants and young children.

24 JOHN KERSHMAN, JULIO VASQUEZ and SYDNEY GOLDSTEIN

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