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Focal positive spikes in electroencephalography
Electroencephalography and Clinical Neurophysiology, 1 9 7 7 , 42 : 1 5 - - 2 5
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© E l s e v i e r / N o r t h - H o l l a n d Scientific P u b l i s h e r s L t d
F O C A L P O S I T I V E SPIKES IN E L E C T R O E N C E P H A L O G R A P H Y
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F U M I S U K E M A T S U O ** a n d J O H N R. K N O T T ***
Electroencephalographic Laboratory, Department of Neurology, University Hospitals and Clinics, University of Iowa School of Medicine, Iowa City, Iowa 52242 (U.S.A.) ( A c c e p t e d for p u b l i c a t i o n : April 26, 1 9 7 6 )
Focal spikes (Maulsby 1971; Chatrian et al. 1974; also see Kooi 1966; Goldensohn 1975) are considered to be the most reliable electroencephalographic (EEG) indication of a cortical epileptogenic lesion (Jasper 1949). Their duration is influenced by factors including the distance between the epileptogenic lesion and the recording electrodes (Brazier 1951; Magnus 1961). Focal sharp waves are epileptiform discharges of a longer duration (Chatrian et al. 1974) and are considered to be less reliable for localization. Cortical spikes and sharp waves are interpreted as summated excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) generated in cortical neurons (Goldensohn and Purpura 1963; Sugaya et al. 1964; Jasper and Stefanis 1965; Creutzfeldt et al. 1966; Goldensohn 1969; Ayala et al. 1973; Creutzfeldt and Houchin 1974; Prince 1974). The polarity of epileptiform discharges recorded from the scalp is usually predominantly negative relative to a suitable reference electrode (Chatrian et al. 1974) and is generally interpreted as indicative of dipoles oriented perpendicularly to the cortical surface with their negative poles near the surface (Tharp 1971; also see Petsche and Brazier * This p a p e r was p r e s e n t e d in p a r t to t h e Central Ass o c i a t i o n o f E l e c t r o e n c e p h a l o g r a p h e r s , Cleveland, Ohio, April 1975. ** P r e s e n t address: D e p a r t m e n t o f N e u r o l o g y , T h e U n i v e r s i t y of U t a h Medical Center, Salt Lake City, Utah 84132. *** P r e s e n t address: D e p a r t m e n t of N e u r o l o g y , Bost o n U n i v e r s i t y S c h o o l o f Medicine, B o s t o n , Mass.
1972; Goldensohn 1975). The deeper positive poles would fail to produce a detectable surface potential (Brazier 1951; Geisler and Gerstein 1961; Magnus 1961). However, Humphrey (1968) pointed out that the correlation between the polarity of spikes and sharp waves and EPSPs is not constant (also see Creutzfeldt 1969; Pollen 1969). Scherrer and CaDet (1972) predicted that transcortical recording would always reveal surface positive transients associated with neuronal discharges while surface bipolar or referential recording would reveal either positive or negative tram sients (also see Fourment et al. 1965; Jami et al. 1968). Their prediction agrees with the theoretical study by Rail and Shepherd (1968) and the illustration by Rosenblueth and Cannon (1942). The literature is sparse in the description of the incidence and significance of focal positive spikes and sharp waves in clinical EEG (Maulsby 1971; Kellaway 1973). They are heterogeneous and could be classified into the following four groups to facilitate the review of their characteristic features. Group 1: Focal positive spikes and sharp waves are occasionally encountered during neonatal seizures (Dreyfus-Brisac and Monod 1964; Dreyfus-Brisac and Ellingson 1972; Monod et al. 1972). The cerebral cortex at birth is anatomically and physiologically iramature because the migration of cortical neurons and myelination have not been completed and the pyramidal cells have poorly developed dendrites except for apical dendrites (Purpura 1962, 1965, 1969, 1971).
16 Studies of cortical evoked potentials have established a predictable sequence of developm e n t during the ontogenesis of humans and animals (Ellingson 1964). However, relatively little information is available in regard to the behavior of epileptic neurons in the neonatal cerebral cortex (Purpura 1969). Volanschi (1972) demonstrated the alteration of polarity of spikes in penicillin foci during ontogenesis. Purpura (1964) postulated that the depolarization of neonatal pyramidal cells limited to the soma and the proximal portions of the apical dendrites might generate bursts of repetitive surface positive sharp waves in isolated hyperexcitable cortex (also see Ferguson and Jasper 1971; Creutzfeldt and Houchin 1974). Group 2: The orientation of the dipoles of the spikes and sharp waves may not be perpendicular to the inner table of the skull. Such is the case with the discharges arising in gyri buried in the depth of the cerebral fissures. Shaw and g o t h (1955), Geisler and Gerstein (1961) and Magnus (1961) predicted that a dipole not perpendicular to the surface of a spherical volume conductor will produce an electrical field with two surface transients of opposite polarities. Maulsby (1971) described an example. Group 3: Adrian and Matthews (1934) demonstrated that a skull defect could affect the electrical field over the scalp, as the area w i t h o u t underlying bone has an increased conductance. The positive ends of dipoles could be detected at the skull defect as a localized surface positive transient (Maulsby 1971; Goldensohn and Koehle 1975; also see Magnus 1961). Group 4: McCulloch (1949) postulated t h a t focal spikes and sharp waves with pred o m i n a n t positivity might result from synaptic transmission from an epileptogenic focus. The initial wave of the cerebral response evoked by the stimulation of corticopetal pathways is positive at the cortical surface and could be attributed to EPSPs arising at the termination of thalamocortical projection fibers (Eccles 1951; Purpura 1959). Under
F. MATSUO, J.R. KNOTT appropriate anesthesia, sensory or thalamic electrical stimulation might evoke repetitive monophasic cortical responses with surface positivity (Chang 1950). Lance and Adams (1963) demonstrated that the initial phase of multiple spikes associated with rnyoclonus was positive at the vertex. However, the polarity of sharp transients resulting from a penicillin focus was negative at the homologous area of the contralateral cerebral cortex (Tharp 1971; also see Crowell 1970). Therefore, the significance of distant synaptic transmission in generation of localized surface positive epileptiform discharges remains to be determined. The purpose of this communication is to describe illustrative cases of focal positive spikes and sharp waves (Groups 1--3) in order to direct attention to this seemingly rare finding and to discuss further its implications.
Method Seven cases of focal positive spikes and sharp waves were found among the EEGs recorded in the EEG Laboratory, University of Iowa Hospitals and Clinics, between January 1973 and April 1975. The patients examined included in-patients and out-patients of all ages. The total number of records during this period was 7,760. Sixteen-channel electroencephalographs were utilized with one exception, in which the record was obtained with a portable 10-channel instrument. Ag-AgCI disc electrodes were applied with collodion, in positions determined by the 10--20 international system (Jasper 1958). Additional electrodes were added when indicated. A standard recording included activation procedures, hyperventilation, intermittent photic stimulation and, whenever feasible, sleep in addition to the waking resting state. All records were visually analyzed. The criteria for focal positive spikes and sharp waves included the following in addition to those defining spikes and sharp waves in the terminology proposed by the Interna-
FOCAL POSITIVE SPIKES tional Federation of Societies for Electroencephalography and Clinical Neurophysiology, except for the polarity (Chatrian et al. 1974): (1) Spikes and sharp waves must be detected in the absence of observable movements. (2) Instrumental phase reversal is repeatedly revealed by linked anteroposterior and transverse bipolar derivations (Jasper 1958). (3) Physiological EEG transients with focal positivity, such as lambda waves and positive occipital sharp transients of sleep (Vignaendra et al. 1974), cerebral transient potentials evoked by extrinsic sensory stimuli and extracerebral potentials such as the electrocardiogram or potentials due to improperly applied electrodes are excluded.
Results and illustrative cases The ages of seven patients at the time of the first EEG with focal positive spikes or sharp waves ranged from 3 days to 52 years and all but one (with a skull defect) were less than 10 years of age. Three patients had more than one record with the finding, and the intervals between the EEGs with positive spikes or sharp waves were 1 day, 6 days and 4 months. All the patients suffered from either generalized or partial seizures. No pathological correlates were available for the condition was fatal in none of the patients and there was no indication for electrocorticography or a neurosurgical intervention.
Group 1: Focal positive spikes and sharp waves during recurrent seizures in early life There were four patients with the ages of 3 days, 17 days, 8 months and 4 years at the time of the first EEG with the finding. All were severely ill but recovered from the acute illness. Two showed p s y c h o m o t o r retardation at later examinations. The etiology could be established in only one child who had developed bilateral subdural h e m a t o m a following a head injury. Clinical seizures consisted mostly of partial seizures with variable elementary
17 m o t o r symptoms but Case 2 had generalized convulsions exclusively. EEGs revealed multifocal seizure discharges, many of which including focal positive spikes and sharp waves, were unaccompanied by clinical manifestations. The number of patients was too small to relate the significance of the polarity and the mu!tifocal nature of the seizure discharges to the prognosis (Rose and Lombroso 1970; Dreyfus-Brisac and Ellingson 1972).
Case 1 This boy, a product of a normal full term pregnancy, developed a generalized tonic convulsion with cyanosis at 36 h of age. An EEG at a local hospital (3 days of age) revealed bilateral independent spikes in temporal and parietal regions. At 2 weeks of age no focal neurological deficits were detected but there was the question of diffuse muscular hypotonicity. E r y t h e m a t o u s vesicles were scattered over the skin. The suggestion of micrognathia was present, but extensive laboratory studies, including serum electrolytes, blood sugar and viral titers, failed to reveal the etiology. An EEG when he was 17 days old revealed frequent partial seizures variably involving the extremities and the head. Many consisted of adversive head movements and deviation of the eyes to either side. Electrographic seizure discharges with and without clinical manifestations were multifocal, most frequently involving the left parasagittal region. The morphology of seizure discharges changed frequently. Spikes and sharp waves with surface pos!tivity were identified at either C3 or C~ electrode without simultaneous focal negative transients (Fig. 1). Seizures were controlled only temporarily with phenobarbital. Subsequently psychomotor retardation became evident, although there was no focal neurological deficit. The frequency of convulsions increased despite an addition of diphenylhydantoin (DPH). Most of the convulsions were tonic and some were associated with deviation of the eyes to either side. Recurrent electrographic seizures were re-
18
F. M A T S U O , J.R. K N O T T
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Fig. 1. E E G of Case 1. Spikes a n d s h a r p waves w i t h surface positivity were localized at C 3 e l e c t r o d e (a: H L F , 35 c/sec; L L F , 1 c/sec) a n d C4 (b: H L F , 15 c/sec; L L F , ] c/sec). No b o d y m o v e m e n t was d e t e c t a b l e .
c o r d e d 4 m o n t h s after the second EEG. T h e y originated in either cerebral hemisphere indep e n d e ntly and were most p r o m i n e n t over the right central and temporal regions, at times associated with adversive head movements. The majority of focal spikes and sharp waves were surface negative but several positive focal sharp waves were f o u n d at C4 electrode. Case 2 This 4-year-old boy with an entirely nega-
tive past and family history, developed sore t h r o a t and was placed on penicillin. He experienced two generalized convulsions 2 days later and was hospitalized. Subsequently he became o b t u n d e d and was transferred to the University Hospital. He was unable to follow c o m m a n d s but neither focal neurological deficit nor evidence of increased intracranial pressure was present. Negative laboratory studies included the complete blood count, blood sugar, serum electrolytes, various viral
F O C A L P O S I T I V E SPIKES
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titers, cerebrospinal fluid (CSF) analysis and cultures. Skull X-rays and a brain scan were not revealing. Generalized convulsions recurred over a 2 week period but were successfully controlled with phenobarbital and DPH. He was unable to speak for 10 days. A diagnosis of viral encephalitis was considered likely. Three EEGs were obtained 4, 10 and 15 days after the first convulsion. The first re-
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vealed several clinical and electrographic seizures in addition to high voltage slow dominant r h y t h m . Although seizure discharges were localized primarily at T3, T4 or Ts electrode with surface positivity, no focal onset could be identified clinically. Focal seizure discharges of two cerebral hemispheres were independent and no simultaneous focal negative discharges were identified. The second EEG was predominated by re-
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F. M A T S U O , J.R. K N O T T
current electrographic seizures over the left cerebral hemisphere without clinical manifestations. There were focal positive sharp waves in the left temporal region (Fig. 2, a) at the onset of the seizure discharges. The third EEG consisted of irregular slow waves w i t h o u t epileptiform discharges. The slow waves were most prominent in the left temporal region. Subsequently he suffered from no convulsions but the anticonvulsants were maintained. His speech improved gradually after
the acute illness. He exhibited hyperactive behavior with occasional temper outbursts. A follow-up EEG performed 8 months later revealed normal findings. Group 2: Focal positive spikes and sharp waves compatible with an electrical field suggesting dipoles not perpendicular to the cerebral convexity. Two patients, both at 5 years of age, revealed this finding. One had suffered from
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Fig. 3. E E G o f Case 4 d u r i n g w a k e f u l n e s s (a) a n d d r o w s i n e s s (b). L o w a m p l i t u d e slow waves are localized over t h e left f r o n t a l region, w h e r e b e t a r h y t h m is p r o m i n e n t . Spikes display i n s t r u m e n t a l p h a s e reversal w i t h positivity at F 3 a n d F 7 e l e c t r o d e s . T h e s h a d e d area in t h e i n s e r t e d d r a w i n g i n d i c a t e s t h e skull d e f e c t d e t e r m i n e d b y p a l p a t i o n in r e l a t i o n to e l e c t r o d e s . H L F , 35 c/sec; L L F , 1 c/sec.
2]
F O C A L P O S I T I V E SPIKES
generalized seizures and the other was suspected of experiencing nocturnal convulsions. Both were healthy with normal intelligence and neurological findings. The long duration of the epileptiform discharges in their EEGs suggested that the location of discharging neurons was distant from the scalp (Brazier 1951; Geisler and Gerstein 1961; Magnus 1961), perhaps in the upper bank of the Syl-
vian fissure, as postulated by Maulsby (1971) (also see Vaughan and Ritter 1970). The morphology of sharp waves was similar to the interictal focal spikes and sharp waves often associated with benign epilepsy in childhood (Gibbs and Gibbs 1960; L o m b r o s o 1967; Beaussart 1972; Blom et al. 1972; Beaumanoir et al. 1974; also see Lerman and Kivity 1975).
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Spikes s h o w i n s t r u m e n t a l p h a s e reversal w i t h positivity at F3 a n d Ca e l e c t r o d e s . H L F , S e c o n d E E G of Case 4 w i t h r e f e r e n c e e l e c t r o d e o n t h e chin. Spikes are i n d i c a t e d b y ara r t i f a c t is also e v i d e n t . Spikes s h o w m a x i m a l positivity a t F 3 e l e c t r o d e a n d m a x i m a l c/sec; L L F , 1 c/sec.
22
F. MATSUO, J.R. KNOTT
Case 3 This girl was first seen at 13 m o n t h s of age after having suffered from three generalized convulsions which were preceded by vomiting and diarrhea o f an u n d e t e r m i n e d cause. A neurological examination, skull X-rays and an EEG were normal. She was placed on phenobarbital. E x c e p t for two akinetic seizures shortly after the initial investigation, she had remained free from recurrent convulsions till her second EEG at 5 years of age. tier d e v e l o p m e n t had been normal physically and intellectually. The second EEG contained sharp waves in the right c e n t r o t e m p o r a l region (Fig. 2, b), which increased during drowsiness and sleep. An analysis of their electrical field revealed maximal positivity at F4 electrode and simultaneous maximal negativity at T4.
an u n d e t e r m i n e d etiological role. An EEG revealed focal slow waves and a p r o m i n e n t beta r h y t h m over the left frontal area. The unusual amplitude of the beta r h y t h m was at t ri but ed to the bone defect. There were focal spikes with maximal positivity at F3 electrode (Fig. 3 and 4, a). On the following day the second EEG was p e r f o r m e d with additional placements of anterior temporal (T, and T2) Silverman 1960) and nasopharyngeal (P~I and P~2) (MacLean 1949) electrodes and a chin reference electrode was added. Focal spikes with maximal positivity at F3 electrode were confirmed and simultaneous focal negative spikes were identified at P~I electrode (Fig. 4, b).
Group 3: Detection of focal positive spikes and sharp waves over a skull defect.
The incidence of focal positive spikes and sharp waves was small (10 of 7,760 records over a 28 m o n t h period or about 1.3 per 1,000). In this series this finding was most c o m m o n in the first decade of life. In contrast to the equivocal clinical significance assigned to 14 and 6 c/sec positive bursts by several authors including Chatrian et al. (1974), all of our patients d e m o n s t r a t e d generalized or partial convulsions. Furthermore, the classification of our patients according to the presumed pathophysiological mechanisms suggested different clinical implications (Groups 1--3). However, a small number of patients in this series prevented a statistical analysis. Whether or not this finding has the same localizing significance as do negative discharges remains unanswered, because no clear correlation is evident between the sites of positive spikes and sharp waves and the ictal clinical manifestations in our patients. However, we believe the presence of focal positive spikes should p r o m p t a diligent search for simultaneous focal negative discharges (Maulsby 1971), which might require additional electrodes such as those in the nasopharyngeal cavity (MacLean 1949; Mayor and Hellen 1964; DeJesus and Masland 1970).
There was one patient (two EEGs) who was the only adult in this series.
Case 4 This man u n d e r w e n t a left frontal cranio t o m y for removal of a meningioma at 15 years of age. A few generalized convulsions occurred immediately postoperatively. He had a habit of mo d er ate drinking. He fell accidentally several m o n t h s before he was seen at the University Hospital (52 years old), and was rendered unconscious for an u n k n o w n period of time. Five mo n t hs later he suddenly felt light-headed while shopping and slumped on the floor, developing a generalized convulsion. He recalled no o t h e r warning and there was no postictal paralysis. DPH was initiated. In addition to a skull d ef e c t and proptosis of the left eye, the sense of smell was absent on the left side. However, neuroradiological investigations excluded a recurrence of the meningioma. A cortical cicatrix was considered to be the anatomical substrate of his convulsive disorder but the recent head t r aum a and a habit of alcoholic c o n s u m p t i o n could have played
Discussion
FOCAL POSITIVE SPIKES Focal positive transients of cerebral origin could easily be confused with artifactual electrical transients due to either an unstable elect r o d e or mo v emen t. Application of additional electrodes might facilitate the establishment of their cerebral origin. The pathophysiological mechanisms underlying focal positive spikes and sharp waves as discussed earlier are in need of experimental confirmation, although t he y have theoretical grounds and appeared useful in their clinical applications. The authors would consider the additional possibility t hat severe diffuse encephalopathies in infancy with r ecur r ent convulsions and high anticonvulsant levels alter the electrogenesis of the soma-dendrite m e m b r a n e of epileptic neurons, thus resulting in epileptiform discharges of inverted polarity ( G r o u p 1) (Sawa et al. 1965; Tharp 1971). However, such a hypothesis as well as those for two o th er groups of patients in this series ( G r o u p 2: with dipoles n o t perpendicular to the cerebral convexity; and G r oup 3: with a skull defect) fails to explain the rare occurrence as indicated by our result, which confirmed the experience of Maulsby (1971) and Goldensohn and Koehle (1975).
23 R6sum6
Courbes avec pointes locales positives en dlectroencdphalographie Les courbes avec pointes focales positives et ondes aigues sont rares en EEG clinique (environ 1,3 pour 1000 EEGs dans cette series), et on les rencont re principalement dans les premiers m o m e n t s de la vie. Nos sept patients souffraient de troubles convulsifs. I1 faut faire la difference entre ces d~charges et les sauts positifs de 14 et de 6 c/ sec. Les oscillations 51ectriques art~factuelles avec positivit~ focale apparente doivent toujours 5tre 5cart~es. A chaque lois que des courbes avec pointes locales positives sont identifiSes, il est conseill~ de chercher la presence de d~charges focales n~gatives simultanees. La litt~rature indique que les courbes avec pointes positives et ondes aigues pourraient ~tre classifi~es selon les m~canismes presumes pathophysiologiques et des cas de patients illustrants ce poi nt o n t 5t~ d~crits.
References Summary Focal positive spikes and sharp waves in clinical EEG are u n c o m m o n ( a bout 1.3 per 1,000 EEGs in this series) and e n c o u n t e r e d chiefly in early life. All of our seven patients suffered from a convulsive disorder. These discharges must be differentiated from 14 and 6 c/sec positive bursts. Artifactual electrical transients with apparent focal positivity must always be ruled out. Whenever focal positive spikes and sharp waves are identified, it is advisable to search for simultaneous :focal negative discharges. The literature indicates t ha t focal positive spikes and sharp waves could be classified according to the presumed pathophysiological mechanisms and illustrative patients were described.
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24 Chatrian, G.E., Bergamini, L., Dondey, M., Klass, D.W., Lennox-Buchthal, M. and Peters~n, I. A glossary of terms most commonly used by clinical electroencephalographers. Electroenceph. clin. Neurophysiol., 1974, 37: 538--548. Creutzfeldt, O.D. Neuronal mechanisms underlying the EEG. In H.H. Jasper et al. (Eds.), Basic mechanisms of the epilepsies. Little, Brown and Co., Boston, Mass., 1969: 397--410. Creutzfeldt, O.D. and Houchin, J. Neuronal basis of EEG-waves. In A. R~mond (Ed.), Handbook of Electroencephalography and Clinical Neurophysiology. Elsevier, Amsterdam, 1974, 2C: 5--55. Creutzfeldt, O.D., Watanabe, S. and Lux, H.D. Relations between EEG phenomena and potentials of single cortical cells. II. Spontaneous and convulsoid activity. Electroenceph. clin. Neurophysiol., 1966, 20: 19--37. Crowell, R.M. Distant effects of a focal epileptogenic process. Brain Res., 1970, 18: 137--154. DeJesus, P.V. and Masland, W.S. The role of nasopharyngeal electrodes in clinical electroencephalography. Neurology (Minneap.), 1970, 20: 869-878. Dreyfus-Brisac, C. and Ellingson, R.J. Prognostic value of the neonatal EEG in full-term newborns. In A. R6mond (Ed.), Handbook of Electroencephalography and Clinical Neurophysiology. Elsevier, Amsterdam, 1972, 15B: 89--100. Dreyfus-Brisac, C. and Monod, N. Electroclinical studies of status epilepticus and convulsions in the newborn. In P. Kellaway and I. Peters~n (Eds.), Neurological and electroencephalographic correlative studies in infancy. Grune and Stratton, New York, 1964: 250--272. Eccles, J.C. Interpretation of action potentials evoked in the cerebral cortex. Electroenceph. clin. Neurophysiol., 1951, 3: 449--464. Ellingson, R.J. Cerebral electrical responses to auditory and visual stimuli in the infant (human and subhuman studies). In P. Kellaway and I. Peters~n (Eds.), Neurological and electroencephalographic correlative studies in infancy. Grune and Stratton, New York, 1964: 78--114. Ferguson, J.H. and Jasper, H.H. Laminar DC studies of acetylcholine-activated epileptiform discharge in cerebral cortex. Electroenceph. clin. Neurophysiol., 1971, 30: 377--390. Fourment, A., Jami, L., Calvet, J. et Scherrer, J. Comparaison de I'EEG recueilli sur le scalp avec l'activit6 61~mentaire des dipoles corticaux radiaires. Electroenceph. clin. Neurophysiol., 1965, 19: 217--229. Geisler, C.D. and Gerstein, G.L. The surface EEG in relation to its sources. Electroenceph. clin. Neurophysiol., 1961, 13: 927--934. Gibbs, E.L. and Gibbs, F.L. Good prognosis of mid-
F. MATSUO, J.R. KNOTT temporal epilepsy. Epilepsia (Amst.), 1960, 1: 448--453. Goldensohn, E.S. Experimental seizure mechanisms. In H.H. Jasper et al. (Eds.), Basic mechanisms of the epilepsies. Little, Brown and Co., Boston, Mass., 1969: 289--298. Goldensohn, E.S. Initiation and propagation of epileptogenic foci. In J.K. Penry and D.D. Daly (Eds.), Advances in neurology. Volume II: Complex partial seizures and their treatment. Raven Press, New York, 1975: 141--162. Goldensohn, E.S. and Koehle, R. EEG interpretation. Futura Publ. Co., Mount Kisco, N.Y., 1975, 186 p. Goldensohn, E.S. and Purpura, D.P. Intracellular potentials of cortical neurons during focal epileptogenic discharges. Science, 1963, 139: 840--842. Humphrey, D.R. Re-analysis of the antidromic cortical response. II. On the contribution of cell discharges and PSPs to the evoked potentials. Electroenceph, clin. Neurophysiol., 1968, 25: 421--442. Jami, L., Fourment, A., Calvet, J. et Thieffry, M. l~tude sur module des m~thodes de d6tection EEG. Electroenceph. clin. Neurophysiol., i968, 24: 130--145. Jasper, H.H. Electrical signs of epileptic discharge. Electroenceph. clin. Neurophysiol., 1949, 1: 11-18. Jasper, H.H. Report of the committee on methods of clinical examination in electroencephalography. Electroenceph. clin. Neurophysiol., 1958, 10: 370--375. Jasper, H.H. and Stefanis, C. Intracellular oscillatory rhythms in pyramidal tract neurones in the cat. Electroenceph. clin. Neurophysiot., 1965, 18: 541--553. Kellaway, P. Automation of clinical electroencephalography: The nature and scope of the problem. In P. Kellaway and I. Peters6n (Eds.), Automation of clinical electroencephalography. Raven Press, New York, 1973: 1--24. Kooi, K.A. Voltage-time characteristic of spikes and other rapid electroencephalographic transients: semantic and morphological considerations. Neurology (Minneap.), 1966, 16: 59--66. Lance, J.W. and Adams, R.D. The syndrome of intention or action myoclonus as a sequel to hypoxic encephalopathy. Brain, 1963, 86: 111--136. Lerman, P. and Kivity, S. Benign focal epilepsy of childhood. Arch. Neurol. (Chic.), 1975, 32: 261-264. Lombroso, C.T. Sylvian seizures and midtemporal spike loci in children. Arch. Neurol. (Chic.), 1967, 17: 52--59. MacLean, P.D. A new nasopharyngeal lead. Electroenceph, clin. Neurophysiol., 1949, 1: 110--113. Magnus, O. On the technique of localization by electroencephalography. Electroenceph. clin. Neuro-
FOCAL POSITIVE SPIKES physiol., 1961, Suppl. 10: 1--35. Maulsby, R.L. Some guidelines for assessment of spikes and sharp waves in EEG tracings. Amer. J. EEG Technol., 1971, 11: 3--16. Mayor, H. and Hellen, M.K. Nasopharyngeal electrode recording. Amer. J. EEG Technol., 1964, 4: 43-50. McCulloch, W. Mechanisms for the spread of epileptic activation of the brain. Electroenceph. clin. Neurophysiol., 1949, 1: 19--24. Monod, N., Pajot, N. and Guidasci, S. The neonatal EEG: Statistical studies and prognostic value in full-term and pre-term babies. Electroenceph. clin. Neurophysiol., 1972, 32: 529--544. Petsche, H. and Brazier, M.A.B. (Eds.). Synchronization of EEG activity in epilepsies. Springer-Verlag, New York, 1972, 431 p. Pollen, D.A. On the generation of neocortical potentials. In H.H. Jasper et al. (Eds.), Basic mechanisms of the epilepsies. Little, Brown and Co., Boston, Mass., 1969: 411--420. Prince, D.A. Neuronal correlates of epileptiform discharges and cortical DC potentials. In A. R6mond (Ed.), Handbook of Electroencephalography and Clinical Neurophysiology. Elsevier, Amsterdam, 1974, 2C: 56--70. Purpura, D.P. Nature of electrocortical potentials and synaptic organizations in cerebral and cerebellar cortex. In C.C. Pfeiffer and J.R. Smythies (Eds.), International review of neurobiology. Academic Press, New York, 1959, 1: 47--163. Purpura, D.P. Synaptic organization of immature cerebral cortex. Wld. Neurol., 1962, 3: 275--293. Purpura, D.P. Relationship of seizure susceptibility to morphologie and physiologic properties of normal and abnormal immature cortex. In P. Kellaway and I. Peters6n (Eds.), Neurological and electroencephalographic correlative studies in infancy. Grune and Stratton, New York, 1964: 117--154. Purpura, D.P. Properties of synaptic activities and spike potentials of neurons in immature neocortex. J. Neurophysiol., 1965, 28: 925--942. Purpura, D.P. Stability and seizure susceptibility of immature brain. In H.H. Jasper et al. (Eds.), Basic mechanisms of epilepsies. Little, Brown and Co., Boston, Mass., 1969: 481--505. Purpura, D.P. Dendrites: heterogeneity in form and function. In A. R6mond (Ed.), Handbook of Elec-
25 troencephalography and Clinical Neurophysiology. Elsevier, Amsterdam, 1971, 1B: 3--17. Rall, W. and Shepherd, G.M. Theoretical reconstruction of field potentials and dendrodendritic synaptic interactions in olfactory bulb. J. Neurophysiol., 1968, 31: 884--915. Rose, A.L. and Lombroso, C.T. Neonatal seizure status. Pediatrics, 1970, 45: 404--425. Rosenblueth, A. and Cannon, W.B. Cortical responses to electric stimulation. Amer. J. Physiol., 1942, 135: 690--741. Sawa, M., Kaji, S. and Usuki, K. Intracellular phenomena in electrically induced seizures. Electroenceph, clin. Neurophysiol., 1965, 19: 248--255. Scherrer, J. and Calvet, J. Normal and epileptic synchronization at the cortical level in the animal. In H. Petsche and M.A.B. Brazier (Eds.), Synchronization of EEG activity in epilepsies. Springer-Verlag, New York, 1972: 112--132. Shaw, J.C. and Roth, M. Potential distribution analysis. II. A theoretical consideration of its significance in terms of electrical field theory. Electroenceph, clin. Neurophysiol., 1955, 7: 285--292. Silverman, D. The anterior temporal electrode and the ten--twenty system. Electroeneeph. clin. Neurophysiol., 1960, 12: 735--737. Sugaya, E., Goldring, S. and O'Leary, J.L. Intracellular potentials associated with direct cortical response and seizure discharge in cat. Electroenceph. clin. Neurophysiol., 1964, 17: 661--669. Tharp, B.R. The penicillin focus. Electroenceph. clin. Neurophysiol., 1971, 31: 45--55. Vaughan, H.G. and Ritter, W. The sources of auditory evoked responses recorded from the human scalp. Electroenceph. clin. Neurophysiol., 1970, 28: 360--367. Vignaendra, V., Matthews, R.L. and Chatrian, G.E. Positive occipital sharp transients of sleep: relationship to nocturnal sleep cycle in man. Electroenceph, clin. Neurophysiol., 1974, 37: 239--246. Volanschi, D. Experimental research on the ontogenetic development of the mechanism of epileptic synchronization. Comparative study on the immature and mature brain. In H. Petsche and M.A.B. Brazier (Eds.), Synchronization of EEG activity in epilepsies. Springer-Verlag, New York, 1972: 189--202.
15
© E l s e v i e r / N o r t h - H o l l a n d Scientific P u b l i s h e r s L t d
F O C A L P O S I T I V E SPIKES IN E L E C T R O E N C E P H A L O G R A P H Y
*
F U M I S U K E M A T S U O ** a n d J O H N R. K N O T T ***
Electroencephalographic Laboratory, Department of Neurology, University Hospitals and Clinics, University of Iowa School of Medicine, Iowa City, Iowa 52242 (U.S.A.) ( A c c e p t e d for p u b l i c a t i o n : April 26, 1 9 7 6 )
Focal spikes (Maulsby 1971; Chatrian et al. 1974; also see Kooi 1966; Goldensohn 1975) are considered to be the most reliable electroencephalographic (EEG) indication of a cortical epileptogenic lesion (Jasper 1949). Their duration is influenced by factors including the distance between the epileptogenic lesion and the recording electrodes (Brazier 1951; Magnus 1961). Focal sharp waves are epileptiform discharges of a longer duration (Chatrian et al. 1974) and are considered to be less reliable for localization. Cortical spikes and sharp waves are interpreted as summated excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) generated in cortical neurons (Goldensohn and Purpura 1963; Sugaya et al. 1964; Jasper and Stefanis 1965; Creutzfeldt et al. 1966; Goldensohn 1969; Ayala et al. 1973; Creutzfeldt and Houchin 1974; Prince 1974). The polarity of epileptiform discharges recorded from the scalp is usually predominantly negative relative to a suitable reference electrode (Chatrian et al. 1974) and is generally interpreted as indicative of dipoles oriented perpendicularly to the cortical surface with their negative poles near the surface (Tharp 1971; also see Petsche and Brazier * This p a p e r was p r e s e n t e d in p a r t to t h e Central Ass o c i a t i o n o f E l e c t r o e n c e p h a l o g r a p h e r s , Cleveland, Ohio, April 1975. ** P r e s e n t address: D e p a r t m e n t o f N e u r o l o g y , T h e U n i v e r s i t y of U t a h Medical Center, Salt Lake City, Utah 84132. *** P r e s e n t address: D e p a r t m e n t of N e u r o l o g y , Bost o n U n i v e r s i t y S c h o o l o f Medicine, B o s t o n , Mass.
1972; Goldensohn 1975). The deeper positive poles would fail to produce a detectable surface potential (Brazier 1951; Geisler and Gerstein 1961; Magnus 1961). However, Humphrey (1968) pointed out that the correlation between the polarity of spikes and sharp waves and EPSPs is not constant (also see Creutzfeldt 1969; Pollen 1969). Scherrer and CaDet (1972) predicted that transcortical recording would always reveal surface positive transients associated with neuronal discharges while surface bipolar or referential recording would reveal either positive or negative tram sients (also see Fourment et al. 1965; Jami et al. 1968). Their prediction agrees with the theoretical study by Rail and Shepherd (1968) and the illustration by Rosenblueth and Cannon (1942). The literature is sparse in the description of the incidence and significance of focal positive spikes and sharp waves in clinical EEG (Maulsby 1971; Kellaway 1973). They are heterogeneous and could be classified into the following four groups to facilitate the review of their characteristic features. Group 1: Focal positive spikes and sharp waves are occasionally encountered during neonatal seizures (Dreyfus-Brisac and Monod 1964; Dreyfus-Brisac and Ellingson 1972; Monod et al. 1972). The cerebral cortex at birth is anatomically and physiologically iramature because the migration of cortical neurons and myelination have not been completed and the pyramidal cells have poorly developed dendrites except for apical dendrites (Purpura 1962, 1965, 1969, 1971).
16 Studies of cortical evoked potentials have established a predictable sequence of developm e n t during the ontogenesis of humans and animals (Ellingson 1964). However, relatively little information is available in regard to the behavior of epileptic neurons in the neonatal cerebral cortex (Purpura 1969). Volanschi (1972) demonstrated the alteration of polarity of spikes in penicillin foci during ontogenesis. Purpura (1964) postulated that the depolarization of neonatal pyramidal cells limited to the soma and the proximal portions of the apical dendrites might generate bursts of repetitive surface positive sharp waves in isolated hyperexcitable cortex (also see Ferguson and Jasper 1971; Creutzfeldt and Houchin 1974). Group 2: The orientation of the dipoles of the spikes and sharp waves may not be perpendicular to the inner table of the skull. Such is the case with the discharges arising in gyri buried in the depth of the cerebral fissures. Shaw and g o t h (1955), Geisler and Gerstein (1961) and Magnus (1961) predicted that a dipole not perpendicular to the surface of a spherical volume conductor will produce an electrical field with two surface transients of opposite polarities. Maulsby (1971) described an example. Group 3: Adrian and Matthews (1934) demonstrated that a skull defect could affect the electrical field over the scalp, as the area w i t h o u t underlying bone has an increased conductance. The positive ends of dipoles could be detected at the skull defect as a localized surface positive transient (Maulsby 1971; Goldensohn and Koehle 1975; also see Magnus 1961). Group 4: McCulloch (1949) postulated t h a t focal spikes and sharp waves with pred o m i n a n t positivity might result from synaptic transmission from an epileptogenic focus. The initial wave of the cerebral response evoked by the stimulation of corticopetal pathways is positive at the cortical surface and could be attributed to EPSPs arising at the termination of thalamocortical projection fibers (Eccles 1951; Purpura 1959). Under
F. MATSUO, J.R. KNOTT appropriate anesthesia, sensory or thalamic electrical stimulation might evoke repetitive monophasic cortical responses with surface positivity (Chang 1950). Lance and Adams (1963) demonstrated that the initial phase of multiple spikes associated with rnyoclonus was positive at the vertex. However, the polarity of sharp transients resulting from a penicillin focus was negative at the homologous area of the contralateral cerebral cortex (Tharp 1971; also see Crowell 1970). Therefore, the significance of distant synaptic transmission in generation of localized surface positive epileptiform discharges remains to be determined. The purpose of this communication is to describe illustrative cases of focal positive spikes and sharp waves (Groups 1--3) in order to direct attention to this seemingly rare finding and to discuss further its implications.
Method Seven cases of focal positive spikes and sharp waves were found among the EEGs recorded in the EEG Laboratory, University of Iowa Hospitals and Clinics, between January 1973 and April 1975. The patients examined included in-patients and out-patients of all ages. The total number of records during this period was 7,760. Sixteen-channel electroencephalographs were utilized with one exception, in which the record was obtained with a portable 10-channel instrument. Ag-AgCI disc electrodes were applied with collodion, in positions determined by the 10--20 international system (Jasper 1958). Additional electrodes were added when indicated. A standard recording included activation procedures, hyperventilation, intermittent photic stimulation and, whenever feasible, sleep in addition to the waking resting state. All records were visually analyzed. The criteria for focal positive spikes and sharp waves included the following in addition to those defining spikes and sharp waves in the terminology proposed by the Interna-
FOCAL POSITIVE SPIKES tional Federation of Societies for Electroencephalography and Clinical Neurophysiology, except for the polarity (Chatrian et al. 1974): (1) Spikes and sharp waves must be detected in the absence of observable movements. (2) Instrumental phase reversal is repeatedly revealed by linked anteroposterior and transverse bipolar derivations (Jasper 1958). (3) Physiological EEG transients with focal positivity, such as lambda waves and positive occipital sharp transients of sleep (Vignaendra et al. 1974), cerebral transient potentials evoked by extrinsic sensory stimuli and extracerebral potentials such as the electrocardiogram or potentials due to improperly applied electrodes are excluded.
Results and illustrative cases The ages of seven patients at the time of the first EEG with focal positive spikes or sharp waves ranged from 3 days to 52 years and all but one (with a skull defect) were less than 10 years of age. Three patients had more than one record with the finding, and the intervals between the EEGs with positive spikes or sharp waves were 1 day, 6 days and 4 months. All the patients suffered from either generalized or partial seizures. No pathological correlates were available for the condition was fatal in none of the patients and there was no indication for electrocorticography or a neurosurgical intervention.
Group 1: Focal positive spikes and sharp waves during recurrent seizures in early life There were four patients with the ages of 3 days, 17 days, 8 months and 4 years at the time of the first EEG with the finding. All were severely ill but recovered from the acute illness. Two showed p s y c h o m o t o r retardation at later examinations. The etiology could be established in only one child who had developed bilateral subdural h e m a t o m a following a head injury. Clinical seizures consisted mostly of partial seizures with variable elementary
17 m o t o r symptoms but Case 2 had generalized convulsions exclusively. EEGs revealed multifocal seizure discharges, many of which including focal positive spikes and sharp waves, were unaccompanied by clinical manifestations. The number of patients was too small to relate the significance of the polarity and the mu!tifocal nature of the seizure discharges to the prognosis (Rose and Lombroso 1970; Dreyfus-Brisac and Ellingson 1972).
Case 1 This boy, a product of a normal full term pregnancy, developed a generalized tonic convulsion with cyanosis at 36 h of age. An EEG at a local hospital (3 days of age) revealed bilateral independent spikes in temporal and parietal regions. At 2 weeks of age no focal neurological deficits were detected but there was the question of diffuse muscular hypotonicity. E r y t h e m a t o u s vesicles were scattered over the skin. The suggestion of micrognathia was present, but extensive laboratory studies, including serum electrolytes, blood sugar and viral titers, failed to reveal the etiology. An EEG when he was 17 days old revealed frequent partial seizures variably involving the extremities and the head. Many consisted of adversive head movements and deviation of the eyes to either side. Electrographic seizure discharges with and without clinical manifestations were multifocal, most frequently involving the left parasagittal region. The morphology of seizure discharges changed frequently. Spikes and sharp waves with surface pos!tivity were identified at either C3 or C~ electrode without simultaneous focal negative transients (Fig. 1). Seizures were controlled only temporarily with phenobarbital. Subsequently psychomotor retardation became evident, although there was no focal neurological deficit. The frequency of convulsions increased despite an addition of diphenylhydantoin (DPH). Most of the convulsions were tonic and some were associated with deviation of the eyes to either side. Recurrent electrographic seizures were re-
18
F. M A T S U O , J.R. K N O T T
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Fig. 1. E E G of Case 1. Spikes a n d s h a r p waves w i t h surface positivity were localized at C 3 e l e c t r o d e (a: H L F , 35 c/sec; L L F , 1 c/sec) a n d C4 (b: H L F , 15 c/sec; L L F , ] c/sec). No b o d y m o v e m e n t was d e t e c t a b l e .
c o r d e d 4 m o n t h s after the second EEG. T h e y originated in either cerebral hemisphere indep e n d e ntly and were most p r o m i n e n t over the right central and temporal regions, at times associated with adversive head movements. The majority of focal spikes and sharp waves were surface negative but several positive focal sharp waves were f o u n d at C4 electrode. Case 2 This 4-year-old boy with an entirely nega-
tive past and family history, developed sore t h r o a t and was placed on penicillin. He experienced two generalized convulsions 2 days later and was hospitalized. Subsequently he became o b t u n d e d and was transferred to the University Hospital. He was unable to follow c o m m a n d s but neither focal neurological deficit nor evidence of increased intracranial pressure was present. Negative laboratory studies included the complete blood count, blood sugar, serum electrolytes, various viral
F O C A L P O S I T I V E SPIKES
19
titers, cerebrospinal fluid (CSF) analysis and cultures. Skull X-rays and a brain scan were not revealing. Generalized convulsions recurred over a 2 week period but were successfully controlled with phenobarbital and DPH. He was unable to speak for 10 days. A diagnosis of viral encephalitis was considered likely. Three EEGs were obtained 4, 10 and 15 days after the first convulsion. The first re-
vl
vealed several clinical and electrographic seizures in addition to high voltage slow dominant r h y t h m . Although seizure discharges were localized primarily at T3, T4 or Ts electrode with surface positivity, no focal onset could be identified clinically. Focal seizure discharges of two cerebral hemispheres were independent and no simultaneous focal negative discharges were identified. The second EEG was predominated by re-
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Fig. 2. a: E E G o f Case 2. A t t h e o n s e t o f t h e seizure discharges surface positive s h a r p waves were clearly localized at T 3 e l e c t r o d e . L a t e r t h e discharges b e c a m e m o r e c o m p l e x , a l t h o u g h t h e y r e t a i n e d p r o m i n e n t positivity in t h e same area. H L F , 35 c/sec; L L F , 1 c/sec, b: E E G of Case 3 in light sleep. R e c u r r e n t s h a r p waves over t h e r i g h t h e m i s p h e r e h a d m a x i m a l positivity at F4 e l e c t r o d e a n d m a x i m a l n e g a t i v i t y at T4, s i m u l t a n e o u s l y . H L F , 70 c/sec; L L F , 1 c/sec.
20
F. M A T S U O , J.R. K N O T T
current electrographic seizures over the left cerebral hemisphere without clinical manifestations. There were focal positive sharp waves in the left temporal region (Fig. 2, a) at the onset of the seizure discharges. The third EEG consisted of irregular slow waves w i t h o u t epileptiform discharges. The slow waves were most prominent in the left temporal region. Subsequently he suffered from no convulsions but the anticonvulsants were maintained. His speech improved gradually after
the acute illness. He exhibited hyperactive behavior with occasional temper outbursts. A follow-up EEG performed 8 months later revealed normal findings. Group 2: Focal positive spikes and sharp waves compatible with an electrical field suggesting dipoles not perpendicular to the cerebral convexity. Two patients, both at 5 years of age, revealed this finding. One had suffered from
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Fig. 3. E E G o f Case 4 d u r i n g w a k e f u l n e s s (a) a n d d r o w s i n e s s (b). L o w a m p l i t u d e slow waves are localized over t h e left f r o n t a l region, w h e r e b e t a r h y t h m is p r o m i n e n t . Spikes display i n s t r u m e n t a l p h a s e reversal w i t h positivity at F 3 a n d F 7 e l e c t r o d e s . T h e s h a d e d area in t h e i n s e r t e d d r a w i n g i n d i c a t e s t h e skull d e f e c t d e t e r m i n e d b y p a l p a t i o n in r e l a t i o n to e l e c t r o d e s . H L F , 35 c/sec; L L F , 1 c/sec.
2]
F O C A L P O S I T I V E SPIKES
generalized seizures and the other was suspected of experiencing nocturnal convulsions. Both were healthy with normal intelligence and neurological findings. The long duration of the epileptiform discharges in their EEGs suggested that the location of discharging neurons was distant from the scalp (Brazier 1951; Geisler and Gerstein 1961; Magnus 1961), perhaps in the upper bank of the Syl-
vian fissure, as postulated by Maulsby (1971) (also see Vaughan and Ritter 1970). The morphology of sharp waves was similar to the interictal focal spikes and sharp waves often associated with benign epilepsy in childhood (Gibbs and Gibbs 1960; L o m b r o s o 1967; Beaussart 1972; Blom et al. 1972; Beaumanoir et al. 1974; also see Lerman and Kivity 1975).
576
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Spikes s h o w i n s t r u m e n t a l p h a s e reversal w i t h positivity at F3 a n d Ca e l e c t r o d e s . H L F , S e c o n d E E G of Case 4 w i t h r e f e r e n c e e l e c t r o d e o n t h e chin. Spikes are i n d i c a t e d b y ara r t i f a c t is also e v i d e n t . Spikes s h o w m a x i m a l positivity a t F 3 e l e c t r o d e a n d m a x i m a l c/sec; L L F , 1 c/sec.
22
F. MATSUO, J.R. KNOTT
Case 3 This girl was first seen at 13 m o n t h s of age after having suffered from three generalized convulsions which were preceded by vomiting and diarrhea o f an u n d e t e r m i n e d cause. A neurological examination, skull X-rays and an EEG were normal. She was placed on phenobarbital. E x c e p t for two akinetic seizures shortly after the initial investigation, she had remained free from recurrent convulsions till her second EEG at 5 years of age. tier d e v e l o p m e n t had been normal physically and intellectually. The second EEG contained sharp waves in the right c e n t r o t e m p o r a l region (Fig. 2, b), which increased during drowsiness and sleep. An analysis of their electrical field revealed maximal positivity at F4 electrode and simultaneous maximal negativity at T4.
an u n d e t e r m i n e d etiological role. An EEG revealed focal slow waves and a p r o m i n e n t beta r h y t h m over the left frontal area. The unusual amplitude of the beta r h y t h m was at t ri but ed to the bone defect. There were focal spikes with maximal positivity at F3 electrode (Fig. 3 and 4, a). On the following day the second EEG was p e r f o r m e d with additional placements of anterior temporal (T, and T2) Silverman 1960) and nasopharyngeal (P~I and P~2) (MacLean 1949) electrodes and a chin reference electrode was added. Focal spikes with maximal positivity at F3 electrode were confirmed and simultaneous focal negative spikes were identified at P~I electrode (Fig. 4, b).
Group 3: Detection of focal positive spikes and sharp waves over a skull defect.
The incidence of focal positive spikes and sharp waves was small (10 of 7,760 records over a 28 m o n t h period or about 1.3 per 1,000). In this series this finding was most c o m m o n in the first decade of life. In contrast to the equivocal clinical significance assigned to 14 and 6 c/sec positive bursts by several authors including Chatrian et al. (1974), all of our patients d e m o n s t r a t e d generalized or partial convulsions. Furthermore, the classification of our patients according to the presumed pathophysiological mechanisms suggested different clinical implications (Groups 1--3). However, a small number of patients in this series prevented a statistical analysis. Whether or not this finding has the same localizing significance as do negative discharges remains unanswered, because no clear correlation is evident between the sites of positive spikes and sharp waves and the ictal clinical manifestations in our patients. However, we believe the presence of focal positive spikes should p r o m p t a diligent search for simultaneous focal negative discharges (Maulsby 1971), which might require additional electrodes such as those in the nasopharyngeal cavity (MacLean 1949; Mayor and Hellen 1964; DeJesus and Masland 1970).
There was one patient (two EEGs) who was the only adult in this series.
Case 4 This man u n d e r w e n t a left frontal cranio t o m y for removal of a meningioma at 15 years of age. A few generalized convulsions occurred immediately postoperatively. He had a habit of mo d er ate drinking. He fell accidentally several m o n t h s before he was seen at the University Hospital (52 years old), and was rendered unconscious for an u n k n o w n period of time. Five mo n t hs later he suddenly felt light-headed while shopping and slumped on the floor, developing a generalized convulsion. He recalled no o t h e r warning and there was no postictal paralysis. DPH was initiated. In addition to a skull d ef e c t and proptosis of the left eye, the sense of smell was absent on the left side. However, neuroradiological investigations excluded a recurrence of the meningioma. A cortical cicatrix was considered to be the anatomical substrate of his convulsive disorder but the recent head t r aum a and a habit of alcoholic c o n s u m p t i o n could have played
Discussion
FOCAL POSITIVE SPIKES Focal positive transients of cerebral origin could easily be confused with artifactual electrical transients due to either an unstable elect r o d e or mo v emen t. Application of additional electrodes might facilitate the establishment of their cerebral origin. The pathophysiological mechanisms underlying focal positive spikes and sharp waves as discussed earlier are in need of experimental confirmation, although t he y have theoretical grounds and appeared useful in their clinical applications. The authors would consider the additional possibility t hat severe diffuse encephalopathies in infancy with r ecur r ent convulsions and high anticonvulsant levels alter the electrogenesis of the soma-dendrite m e m b r a n e of epileptic neurons, thus resulting in epileptiform discharges of inverted polarity ( G r o u p 1) (Sawa et al. 1965; Tharp 1971). However, such a hypothesis as well as those for two o th er groups of patients in this series ( G r o u p 2: with dipoles n o t perpendicular to the cerebral convexity; and G r oup 3: with a skull defect) fails to explain the rare occurrence as indicated by our result, which confirmed the experience of Maulsby (1971) and Goldensohn and Koehle (1975).
23 R6sum6
Courbes avec pointes locales positives en dlectroencdphalographie Les courbes avec pointes focales positives et ondes aigues sont rares en EEG clinique (environ 1,3 pour 1000 EEGs dans cette series), et on les rencont re principalement dans les premiers m o m e n t s de la vie. Nos sept patients souffraient de troubles convulsifs. I1 faut faire la difference entre ces d~charges et les sauts positifs de 14 et de 6 c/ sec. Les oscillations 51ectriques art~factuelles avec positivit~ focale apparente doivent toujours 5tre 5cart~es. A chaque lois que des courbes avec pointes locales positives sont identifiSes, il est conseill~ de chercher la presence de d~charges focales n~gatives simultanees. La litt~rature indique que les courbes avec pointes positives et ondes aigues pourraient ~tre classifi~es selon les m~canismes presumes pathophysiologiques et des cas de patients illustrants ce poi nt o n t 5t~ d~crits.
References Summary Focal positive spikes and sharp waves in clinical EEG are u n c o m m o n ( a bout 1.3 per 1,000 EEGs in this series) and e n c o u n t e r e d chiefly in early life. All of our seven patients suffered from a convulsive disorder. These discharges must be differentiated from 14 and 6 c/sec positive bursts. Artifactual electrical transients with apparent focal positivity must always be ruled out. Whenever focal positive spikes and sharp waves are identified, it is advisable to search for simultaneous :focal negative discharges. The literature indicates t ha t focal positive spikes and sharp waves could be classified according to the presumed pathophysiological mechanisms and illustrative patients were described.
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