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Physiologically versus electrically evoked somatosensory cortical potentials
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( I ) there are consistent differences in the properties of electrodes from d i f f e r e n t manufacturers, (2) e l e c t r o l y t i c treatment improves the performance of a l l electrodes and tends to lessen the differences among then, and (3) both active and passive electrode cable shields are e f f e c t i v e in reducing extraneous l i n e noise.
F77 DISTURBANCESOF SOME INTERHEMISPHERAL INTERACTION AFTER ISCHAEMIC STROKE DROBNY, M., PITHOVA, B., FUNDAREK, J., Neurologic C l i n i c Faculty of Medicine, Martin, CSSR The authors investigated 31 patients after ischaemic hemispheral stroke by means of the passive sinusoidal forearm movements, of the evaluation of part i c u l a r SEPs components and of the polyelectromyographical r e g i s t r a t i o n of the isometric recruitment paradigms of the leg muscles during exteroceptive i r r i t a t i o n of the Babinski's zone. Excessive deviations from control patterns in the coordination of voluntary and r e f l e x a c t i v i t i e s in the followed parameters were found. Similar disturbances also appeared in the sensory i n t e r action between the hemispheres, as evaluated, f o l l o w i n g the late SEPs components i p s i l a t e r a l l y to the median nerve s t i m u l a t i o n . B i l a t e r a l l y ( i . e . also in so-called "unaffected" leg) pathologic paradigm of the isometric leg muscle contractions were found, together with high values of the basic r e f l e x muscle tonus, as ascertained by the passive sinusoidal movements. Reflex tonus values did not correlate with the grade of pathologic changes of the recruitment leg muscles paradigmes: high grade of the pathologic paradigm was often found together with the low r e f l e x muscle tonus in the EMG picture but with high grade of the muscular resistance at the c l i n i c a l i n v e s t i g a t i o n performed by means of the passive manual muscle stretch.
F78 PHYSIOLOGICALLYVERSUS ELECTRICALLY EVOKED SOMATOSENSORYCORTICAL POTENTIALS DUCATI A, SCHIEPPATI M., I n s t i t u t e s of Neurosurgery and of Human Physiology, U n i v e r s i t y of Milano, Italy A simple method for skin s t i m u l a t i o n has been implemented using an a i r puff with c o n t r o l l e d i n t e n s i t y and time course. In 10 normal volunteers, the somatosensory c o r t i c a l potential (SCP) has been obtained using an e l e c t r i c a l and a physiological stimulus on the r i g h t index. SCP from e l e c t r i c a l s t i m u l i were in agreement with most l i t e r a t u r e data. P h y s i o l o g i c a l l y evoked SCP d i f f e r e d somewhat; the f i r s t negative d e f l e c t i o n could be measured with a 3 ÷ 0.5 msec delay as compared to e l e c t r i c a l l y evoked SCP, t h i s latency being Eonsistent with receptor'stransducing time; the N20-P30 complex was ampler by 1.2 pV on the mean; f i n a l l y , the primary response was followed by larger l a t e waves. In the same subject, repeated tests were v i r t u a l l y i d e n t i c a l , provided that the stimu l a t i o n and recording c h a r a c t e r i s t i c had not been changed. The SCP from an a i r puff in the second trigeminal branch has also been recorded in the same subjects. This has a t y p i c a l waveform, s t a r t i n g with a negative d e f l e c t i o n at I I + 1.5 msec, followed by 5 p o s i t i v e peaks and a large negative wave at I00 msec.-
$74
D i f f e r e n t somatosensory pathways may be involved in the two methods, thus a l lowing a better i n s i g h t in the sensation process in man. The p h y s i o l o g i c a l l y evoked SCP w i l l prove useful in several problems concerning c l i n i c a l and paed i a t r i c neurology and in neurosurgery.
F79 CAUTIONABOUT THE USE OF PLASMA EXCHANGE IN THE TREATMENTOF MYASTHENIA GRAVIS DURELLI,L., BERGAMINI,L. and COCITO,D., Clinica Neurologica Universita di Torino, I t a l y The probable autoimmune pathogenesis of Myasthenia Gravis(MG) has prompted the use of immunosuppressant therapies such as immunosuppressive drugs and plasma exchange (PE). We have treated 8 patients with the combined use of PE, prednisone and/or cyclophosphamide. Patients received serial c l i n i c a l EMG evaluations and the chronological correlations between therapy and c l i n i c a l EMG evolution were studied. Before the improvement of myasthenic symptoms (observed in a l l patients) a short i n i t i a l phase of c l i n i c a l EMG d e t e r i o r a t i o n was noted in 6 (out of 8) patients. In 2 patients the worsening was so severe to p r e c i p i t a t e a "myasthenic c r i s i s " . In a l l cases the worsening was temporary and i t s possible r e l a t i o n s h i p s to an abrupt change of the level of a n t i c h o l i n e r g i c receptor antibodies are discussed. The possible occurrence of an i n i t i a l d e f i n i t e d e t e r i o r a t i o n of myasthenic symptoms during a PE course must be c l e a r l y kept in mind by a l l physicians en- ~ gaged in th~s complex therapeutic procedure.
F 80 SCALP RECORDEDSOMATO-SENSORYEVOKED POTENTIALS DURING SPINAL SURGERY EBNER,A.l , BREITNER,S.2 and MATSEN,K.A. 2, I . Dept. of Neurology, Albert-Ludwigs-Universit~Freiburg~ 2. Dept. of Orthopedics~ L u d w i g - M a x i m i l i a n - U n i v e r s i t y , Munich , FRG Besides the diagnostic usefulness of short latency evoked p o t e n t i a l s in c l i n i cal neurology, a f u r t h e r promising a p p l i c a t i o n might be monitoring central nervous pathways during possibly r i s k y operations. We report on the results of i n t r a o p e r a t i v e l y recorded t i b i a l nerve evoked p o t e n t i a l s in 14 patients undergoing spinal surgery (lo patients with s c o l i o s i s and 4 with s p o n d y l o l i s t h e s i s , age 12 to 52 years, mean 22 years). Posterior t i b i a l nerve was stimulated at the ankle and responses were obtained by scalp electrodes f i x e d at Cz with a f r o n t a l reference at Fz. Recordinq was started a f t e r induction of narcosis repeated every 2o minutes and continuously recorded during the c r i t i c a l phases of the operation. A l l patients showed a stable i n i t i a l P4o-N5o-complex which was preserved during the whole surgical procedure. In contrast, the immediately f o l l o w i n g P6o-N7o complex showed a variable wave form in 6 out of the 14 patients. The difference in s t a b i l i t y of t i b i a l nerve evoked potential components w i l l be discussed in terms of the assumed generators of the several components.
( I ) there are consistent differences in the properties of electrodes from d i f f e r e n t manufacturers, (2) e l e c t r o l y t i c treatment improves the performance of a l l electrodes and tends to lessen the differences among then, and (3) both active and passive electrode cable shields are e f f e c t i v e in reducing extraneous l i n e noise.
F77 DISTURBANCESOF SOME INTERHEMISPHERAL INTERACTION AFTER ISCHAEMIC STROKE DROBNY, M., PITHOVA, B., FUNDAREK, J., Neurologic C l i n i c Faculty of Medicine, Martin, CSSR The authors investigated 31 patients after ischaemic hemispheral stroke by means of the passive sinusoidal forearm movements, of the evaluation of part i c u l a r SEPs components and of the polyelectromyographical r e g i s t r a t i o n of the isometric recruitment paradigms of the leg muscles during exteroceptive i r r i t a t i o n of the Babinski's zone. Excessive deviations from control patterns in the coordination of voluntary and r e f l e x a c t i v i t i e s in the followed parameters were found. Similar disturbances also appeared in the sensory i n t e r action between the hemispheres, as evaluated, f o l l o w i n g the late SEPs components i p s i l a t e r a l l y to the median nerve s t i m u l a t i o n . B i l a t e r a l l y ( i . e . also in so-called "unaffected" leg) pathologic paradigm of the isometric leg muscle contractions were found, together with high values of the basic r e f l e x muscle tonus, as ascertained by the passive sinusoidal movements. Reflex tonus values did not correlate with the grade of pathologic changes of the recruitment leg muscles paradigmes: high grade of the pathologic paradigm was often found together with the low r e f l e x muscle tonus in the EMG picture but with high grade of the muscular resistance at the c l i n i c a l i n v e s t i g a t i o n performed by means of the passive manual muscle stretch.
F78 PHYSIOLOGICALLYVERSUS ELECTRICALLY EVOKED SOMATOSENSORYCORTICAL POTENTIALS DUCATI A, SCHIEPPATI M., I n s t i t u t e s of Neurosurgery and of Human Physiology, U n i v e r s i t y of Milano, Italy A simple method for skin s t i m u l a t i o n has been implemented using an a i r puff with c o n t r o l l e d i n t e n s i t y and time course. In 10 normal volunteers, the somatosensory c o r t i c a l potential (SCP) has been obtained using an e l e c t r i c a l and a physiological stimulus on the r i g h t index. SCP from e l e c t r i c a l s t i m u l i were in agreement with most l i t e r a t u r e data. P h y s i o l o g i c a l l y evoked SCP d i f f e r e d somewhat; the f i r s t negative d e f l e c t i o n could be measured with a 3 ÷ 0.5 msec delay as compared to e l e c t r i c a l l y evoked SCP, t h i s latency being Eonsistent with receptor'stransducing time; the N20-P30 complex was ampler by 1.2 pV on the mean; f i n a l l y , the primary response was followed by larger l a t e waves. In the same subject, repeated tests were v i r t u a l l y i d e n t i c a l , provided that the stimu l a t i o n and recording c h a r a c t e r i s t i c had not been changed. The SCP from an a i r puff in the second trigeminal branch has also been recorded in the same subjects. This has a t y p i c a l waveform, s t a r t i n g with a negative d e f l e c t i o n at I I + 1.5 msec, followed by 5 p o s i t i v e peaks and a large negative wave at I00 msec.-
$74
D i f f e r e n t somatosensory pathways may be involved in the two methods, thus a l lowing a better i n s i g h t in the sensation process in man. The p h y s i o l o g i c a l l y evoked SCP w i l l prove useful in several problems concerning c l i n i c a l and paed i a t r i c neurology and in neurosurgery.
F79 CAUTIONABOUT THE USE OF PLASMA EXCHANGE IN THE TREATMENTOF MYASTHENIA GRAVIS DURELLI,L., BERGAMINI,L. and COCITO,D., Clinica Neurologica Universita di Torino, I t a l y The probable autoimmune pathogenesis of Myasthenia Gravis(MG) has prompted the use of immunosuppressant therapies such as immunosuppressive drugs and plasma exchange (PE). We have treated 8 patients with the combined use of PE, prednisone and/or cyclophosphamide. Patients received serial c l i n i c a l EMG evaluations and the chronological correlations between therapy and c l i n i c a l EMG evolution were studied. Before the improvement of myasthenic symptoms (observed in a l l patients) a short i n i t i a l phase of c l i n i c a l EMG d e t e r i o r a t i o n was noted in 6 (out of 8) patients. In 2 patients the worsening was so severe to p r e c i p i t a t e a "myasthenic c r i s i s " . In a l l cases the worsening was temporary and i t s possible r e l a t i o n s h i p s to an abrupt change of the level of a n t i c h o l i n e r g i c receptor antibodies are discussed. The possible occurrence of an i n i t i a l d e f i n i t e d e t e r i o r a t i o n of myasthenic symptoms during a PE course must be c l e a r l y kept in mind by a l l physicians en- ~ gaged in th~s complex therapeutic procedure.
F 80 SCALP RECORDEDSOMATO-SENSORYEVOKED POTENTIALS DURING SPINAL SURGERY EBNER,A.l , BREITNER,S.2 and MATSEN,K.A. 2, I . Dept. of Neurology, Albert-Ludwigs-Universit~Freiburg~ 2. Dept. of Orthopedics~ L u d w i g - M a x i m i l i a n - U n i v e r s i t y , Munich , FRG Besides the diagnostic usefulness of short latency evoked p o t e n t i a l s in c l i n i cal neurology, a f u r t h e r promising a p p l i c a t i o n might be monitoring central nervous pathways during possibly r i s k y operations. We report on the results of i n t r a o p e r a t i v e l y recorded t i b i a l nerve evoked p o t e n t i a l s in 14 patients undergoing spinal surgery (lo patients with s c o l i o s i s and 4 with s p o n d y l o l i s t h e s i s , age 12 to 52 years, mean 22 years). Posterior t i b i a l nerve was stimulated at the ankle and responses were obtained by scalp electrodes f i x e d at Cz with a f r o n t a l reference at Fz. Recordinq was started a f t e r induction of narcosis repeated every 2o minutes and continuously recorded during the c r i t i c a l phases of the operation. A l l patients showed a stable i n i t i a l P4o-N5o-complex which was preserved during the whole surgical procedure. In contrast, the immediately f o l l o w i n g P6o-N7o complex showed a variable wave form in 6 out of the 14 patients. The difference in s t a b i l i t y of t i b i a l nerve evoked potential components w i l l be discussed in terms of the assumed generators of the several components.