PubMed Health⌕ Search

Biomedical subjects

M Georgesco

Publications and source records attributed to M Georgesco.

At least 19 recordsLinked to original sources
PubMed2001

Short latency facilitation between pairs of threshold magnetic stimuli studied in amyotrophic lateral sclerosis.

The aim of the present study was to investigate the effects of short latency facilitation between pairs of threshold magnetic stimuli on the motor cortex of amyotrophic lateral sclerosis (ALS) patients, at an interstimulus interval (ISI) of 1-5 ms. As compared to controls, the facilitatory effects normally recorded at ISI 1 and 3 ms were considerably reduced. This suggested that the neuronal circuitry responsible for these effects, which is supposed to be the same as those generating I-waves, is impaired in ALS.

Differential Threshold↗
PubMed2000

[Spontaneous electromyographic activity. Practical importance].

Spontaneous activities are a major semeiologic sign in electromyography. The present article deals with the different aspects recorded in practice in normal and pathological cases. There are two types of spontaneous activities, those related to motor unit hyperactivity (fasciculations and myokymia) and those related to the hyperactivity of one or more muscle fibers: fibrillations, positive sharp waves, myotonic discharges and complex repetitive discharges. In the first case the lesion is located in the axone and in the second in the membrane of the muscle fibers; All theories related to the cells' abnormalities share a common feature: spontaneous activities result from abnormal firing of the membrane action potential of muscular fibers. This functional abnormality may results from different types of lesions within the cells' membrane and determines the aspects of spontaneous activities. Impaired function of muscular cells' membranes can be produced by denervation or lesion of the membrane structure itself. The latter can be multiple and linked with the membrane proteins (such as laminine or dystrophin as in AIDS diseases) or with ion channel disturbances. Multiple membrane cell alterations may produce the same kind of spontaneous activity; for instance, myotonic discharges have the same morphology in Thomsen and Steinert's disease despite their different mechanisms and fibrillations seen in denervations and myopathies. The practical consequences are discussed and a new classification of these spontaneous activities is proposed.

Action Potentials↗
PubMed2000

Motor cortical dysfunction disclosed by single and double magnetic stimulation in patients with fibromyalgia.

OBJECTIVE: To investigate the motor cortex by single and double magnetic stimulation, in patients with fibromyalgia. METHODS: Thirteen patients with fibromyalgia and 13 age-matched healthy subjects were examined. We evaluated, in both limbs, motor evoked potential (MEP) latency and amplitude and the MCA/MPA ratio, i.e. MEP cortical amplitude (MCA) /maximal peripheral amplitude of the M response (MPA), the central conduction time (TCC) and the length of the silent period (SP). With double magnetic stimulation, different time intervals between shocks were used: with delays between shocks of 4, 25, 55 and 85 ms, the intensities of the conditioning shock were 80% the relaxed threshold. With delays between shocks of 55, 85, 100, 155, 200, 255 and 355 ms, the intensities of the conditioning shocks were set at 150% the relaxed threshold. In all cases, the intensity of the test shock was 150% the relaxed threshold. The results were also compared with those obtained in 5 women affected by rheumatoid arthritis (RA). RESULTS: As compared to control, the cortical relaxed threshold was enhanced on both sides and limbs (P<0.05). The cortical silent period recorded with single magnetic stimulation was reduced in the upper limbs (P = 2.7x10(-11)) and lower limbs (both sides P = 3.6x10(-5)). The other parameters investigated were normal. With double magnetic stimulation, facilitatory phenomena were absent in fibromyalgic patients and the inhibitory responses recorded with a delay of 155 ms were reduced (P = 0.0052). No significant differences were noted between FM and RA patients. CONCLUSION: This study demonstrated motor cortical dysfunction in patients with fibromyalgia involving excitatory and inhibitory mechanisms. This indicates motor cortical involvement and supports the hypothesis of aberrant central pain mechanisms. The absence of differences between FM and RA suggest that the lesions were not specific and could be related to chronic pain disorders within the central nervous system.

Adult↗
PubMed1999

[Evoked motor potentials obtained with double magnetic cortical stimulation: techniques and interpretation].

UNLABELLED: The technique of motor evoked potentials (MEP) obtained with single and double magnetic stimulation of the motor cortex in man has considerably improved over the past decade. We present the techniques and parameters involved in double magnetic stimulation for clinical purposes. METHOD: The conditioning-test design is used to study modifications in the amplitudes of the muscular responses to the "test" shock, recorded on the first dorsal interosseus muscle. Enhanced amplitudes of conditioned responses indicate facilitation, reduced response inhibition. RESULTS: The effects vary according to the shock intensity, the delay between shocks and the position of the conditioning coil. The latter may be located at the same place as the test shock (to test interneural circuitry related to pyramidal tract), on the hand area opposite the test shock (to test interhemispheric influences), or over the cerebellar area contralateral to the test side (to test the effect of cerebellar stimulations over the motor cortex). When the coils were located on the same cortical hand area there was facilitation when the intensities were both set at the threshold with an interstimulus interval (ISI) between 1 and 2.5-3 ms. At conditioning shock intensities below the threshold and the test shock 150% above, inhibition occurred at ISI 1-5 ms followed by facilitation at ISI 15-35 ms. When the intensities of both shocks were 150% above threshold, there were two clear cut individual responses at ISI above 10 ms; facilitation was recorded at ISI 15-35 ms, and inhibition between 55 and 255 ms. When the conditioning coil was located on the opposite hand area from the test shock (conditioning shock intensity supramaximal, test shock intensity above the threshold), ISI 1-5 ms facilitation occurred followed by inhibition up to ISI 30 ms. When the conditioning shock (intensity supramaximal) was located on the cerebellar area contralateral to the test side (intensity above the threshold), inhibition occurred at ISI 5 ms. CONCLUSIONS: Double magnetic stimulations delivered over the same cortical area reflect facilitatory and inhibitory influences over the pyramidal tract controlled by interneurons, i.e., these tests investigate the intrinsic circuitry of the motor strip. Double magnetic stimulations delivered on each motor area study interhemispheric influences mediated by the corpus callosum, which are facilitatory and inhibitory. Double magnetic stimulations delivered on the cerebellar area demonstrates inhibitory influences over the contralateral cerebral motor cortex.

Adult↗
PubMed1998

Double magnetic stimulation of the motor cortex in amyotrophic lateral sclerosis.

OBJECTIVES: To study the motor cortex circuitry and the motor interhemispheric influences with double magnetic stimulation in patients affected by amystrophic lateral sclerosis. METHODS: We investigated the motor cortex in 21 amyotrophic lateral sclerosis patients (ALS, 10 with bulbar and 11 with spinal onset) with double magnetic stimulation (one shock in each hand area) with 2, 4, 6, 11 and 15 ms delay between shocks and paired magnetic stimulation (both shocks in the same area), with 4, 15, 25, 35, 55, 85, 100, 155, 200 and 255 ms delays, and compared the results with those obtained in normal subjects. RESULTS: Double magnetic stimulation showed reduced interhemispheric facilitatory influences (maximal at 4 ms delay between shocks) when the test shock was applied on the left hemisphere in all patients; whereas no significant differences were observed compared to control (P > 0.05) when it was applied on the right hemisphere in both forms. Inhibitory effects (maximal at 11 ms delay between shocks) were reduced in all patients for both hemispheres (P < 0.05). Paired magnetic stimulations showed decreased inhibitory influences at 100-155 ms delay between shocks. Compared to control, the difference was significant in bulbar (P < 0.05) and spinal onset, but not between onset forms (P > 0.05). Inhibitory effects recorded with a short delay between shocks (4 ms) were not significantly modified in both forms of onset (P > 0.05) as compared to control. There were no facilitatory influences at 15 and 35 ms delays between shocks. CONCLUSIONS: The results suggest that under these test conditions inhibition and facilitation were reduced in the motor cortex in ALS. As inhibitory effects were affected differently, two distinct cortical circuitries could be involved for short and long delays. As GABA neurons altered in ALS have been identified as a subpopulation reactive to parvalbumin, and since only inhibitory effects recorded with long delay between shocks were impaired in ALS, we suggest that this subpopulation of GABA neurons may be involved in the genesis of inhibitory effects recorded with a long delay between shocks.

Adult↗
PubMed1997

Somatosensory evoked potentials elicited by stimulation of lower-limb nerves in amyotrophic lateral sclerosis.

To determine lower limb somatosensory modifications in amyotrophic lateral sclerosis (ALS), we studied somatosensory evoked potentials (SEPs) elicited by stimulation of tibial posterior nerves (TP), sural nerves (SN), saphenous internous nerves (SA), and medial plantar nerves (PL) of both limbs in 24 ALS patients, and compared the results with those from 17 normal subjects. Responses were recorded according to the international 10-20 system. Normal sensory conduction velocities of SN, SA and PL and H reflexes in soleus muscles were prerequisites for patient inclusion in this study. The results showed marked alterations in SEPs cortical components of all lower limb nerves, which could be related to abnormal sensory transmission (after spinal N22), or cortical abnormalities. We put forward the hypothesis of impairment of pyramidal control of the sensory system and Clark's column involvement to explain such anomalies. It was concluded that SEPs abnormalities in the lower limbs are a common feature in ALS.

Aged↗
PubMed1996

[Alterations of various parameters of evoked motor potentials in amyotrophic lateral sclerosis].

To assess their interest, we studied different motor evoked potentials (MEP) parameters in 18 amyotrophic lateral sclerosis (ALS) patients and compared them to those obtained in 20 subjects unaffected by neurological diseases: cortical threshold (CT), latency and amplitude of primary responses (PR), central conduction time (CCT), silent period (SP) contralateral to the stimulated cortex and late muscular responses (LMR). In normal subjects MEP parameters were in agreement with those described in the literature, except for LMR. These were only recorded in upper limbs with latencies around 200 ms in 9 out of 20 subjects. In ALS patients, LMR were not modified as compared to normal subjects. Except for mean CCT, in upper and lower limbs, all parameters were altered. We conclude that all MEP parameters are useful in ALS and disclose the involvement of the entire pyramidal tract in this disease.

Amyotrophic Lateral Sclerosis↗
PubMed1996

Motor evoked potentials (MEPs): evaluation of the different types of responses in amyotrophic lateral sclerosis and primary lateral sclerosis.

We studied different motor evoked potential parameters: cortical threshold (CT), primary response (PR) latency and amplitude and central conduction time (CCT) at rest and after maximal voluntary contraction of the target muscles, silent period (SP) and late muscular responses (LMR) in 21 normal subjects 42- to 75-years old and compared the results to those of 17 patients with motor disease (10 amyotrophic lateral sclerosis, ALS and 7 primary lateral sclerosis (PLS). We report for the first time in patients affected by motor diseases, LMRs were similar to controls. We found abnormalities in both ALS and PLS: enhanced cortical threshold, reduced PR amplitude during maximal voluntary contraction of target muscles compared to rest and shorter SP. CCT was slightly different: in ALS it was normal or undetermined (because of lack of the PR), while it was normal, enhanced or undetermined in PLS. We conclude that except for LMR, additional parameters would be useful for studying motor diseases: CT (reflecting excitability of the central cells), PR amplitudes and SP (disclosing inhibitory pathway disturbances in pyramidal tract diseases).

Adult↗
PubMed1996

Interhemispheric facilitation and inhibition studied in man with double magnetic stimulation.

Double magnetic stimulation was used to investigate the influence of a conditioning magnetic shock, applied to the hand motor area, on the size of the EMG response of the first dorsal interosseous (FDI) muscle elicited by magnetic test stimulation, applied to the same area of the opposite hemisphere, in 55 subjects unaffected by neurological disease. Both hemispheres were studied and compared at different intervals between shocks, ranging from 1-15 ms. With short intervals between shocks (1-5 ms), the EMG response to the target muscle of the test shock was increased (facilitation); it diminished after 6 ms (inhibition). Facilitatory effects started at 1-2 ms between shocks and lasted up to 5 ms between shocks. They were mainly present on one side; only 11/35 subjects tested from 1 to 5 ms between shocks had bilateral facilitatory effects. No significant differences between right and left hemispheres and sexes were noted. The conduction time to mediate facilitation between hemispheres was estimated at 8-9 ms. No facilitation occurred when the electrical test shock was conditioned by a magnetic shock, or when the magnetic test shock was conditioned by an electrical shock. We conclude that facilitation takes place at the cortical level since electrical stimulation is known to act on axons and magnetic stimulation on neurons. Facilitation did not occur when the magnetic conditioning coil was moved away from the motor area, suggesting that it requires pathways that link these areas, e.g. the corpus callosum. Facilitation was observed with muscles at rest; it disappeared when the FDI muscle was contracted. Inhibition occurred after 6 ms between shocks. It was noted in both hemispheres, in all subjects tested with no gender differences observed. The depth of inhibition increased with an increase in the interval between shocks. It clearly started at 6 ms between shocks in both hemispheres. The conduction time between hemispheres for inhibitory phenomena was estimated at 13 ms. We concluded that interhemispheric facilitatory and inhibitory phenomena are present in man, as suggested by experimental data in animals. For clinical purposes, we propose an interval of 4 ms between shocks to investigate facilitatory interhemispheric influences and 11 ms for inhibitory effects.

Adult↗
PubMed1994

[Value of a rapid method to determine muscle fiber density in amyotrophic lateral sclerosis].

We shortened single fiber electromyography examination by evaluating fiber density, jitter and block numbers in the 10th and the 20th different needle positions in the extensor digitorum communis. The results obtained in 15 normal subjects and 12 amyotrophic lateral sclerosis patients were comparated. There were no significant differences with the 10th and 20th needle positions in normal subjects or in patients. This method diminished patient discomfort and shortened the examination time.

Adult↗
PubMed1994

[Somatosensory evoked potentials in amyotrophic lateral sclerosis and primary lateral sclerosis].

Somatosensory evoked potentials (SEPs) were studied in 21 cases of amyotrophic lateral sclerosis (ALS) and 7 cases of primary lateral sclerosis (PLS). Despite the lack of clinical sensory abnormalities, SEPs showed abnormalities in both diseases: lack or delay of some components. In ALS these abnormalities indicate widespread sensory disturbance. In PLS only, the Brodmann area 4 seems to be affected.

Adult↗
PubMed1992

[Electromyographic, histoenzymologic and immunocytochemical aspects of affected muscles in HIV infection. Observations of five cases].

In 5 acquired-immunodeficiency syndrome (AIDS) cases without peripheral neuropathy, we observed myogen clinical signs (diffuse amyotrophy of lower limbs or cramps) or an isolated increase in seric enzyme (LDH, CK). EMG abnormalities were observed in all cases: spontaneous activities (fibrillations and positive sharp waves) in 5 cases, myogenic signs in 2 case. Muscular biopsies were normal in 3 cases and showed myopathic changes in 1 case and polymyositis in another case. Antidystrophin and antilaminin antibodies reactions were altered in 1 case. The spontaneous activities together with these modifications could be in favour of a lesion at the membrane level.

Acquired Immunodeficiency Syndrome↗
PubMed1988

[Radicular evoked potential. Peroperative recording in lumbar disk hernias].

The evoked compound action potential of lumbar nerve roots after posterior tibial nerve stimulation at the ankle during operation were studied in 10 patients with lumbar disc herniation. The recording needle electrode was inserted into compressed the nerve root before and after excision of disc herniation. The evoked nerve root action potentials consisted of a positive-negative complex. Before excision, this predominant positive complex was recorded in every patient with a mean peak latency of P1 at 16.64 +/- 1.69 msec, and a mean peak to peak amplitude of P1-N1 of 1.94 +/- 0.52 microv. In three cases with migratory disc herniation, the P1-N1 complex was followed by smaller negative component. After excision of disc herniation, the amplitude of the P1-N1 complex decreased significantly with no significant latency modification. The second negative component was not recorded in the three cases with migratory disc herniation. The recording of nerve root evoked potential during operation is of interest for diagnostic purposes. In addition, it allows electrophysiological monitoring of nerve root traumatism during operation procedures.

Adult↗
PubMed1987

Normal latency values of early cortical somatosensory evoked potentials in children.

Somatosensory evoked potentials (SEPs) after median and posterior tibial nerve stimulation were studied in 172 children ranging in age from 1 day to 16 years for the purpose of obtaining normal reference values, for use in analysing pathological cases. The mean onset and peak latencies of the N wave after median nerve stimulation and of the P wave after posterior tibial nerve stimulation were calculated for 12 age groups. N and P latencies decreased from birth to 3 years of age, when they reached their minimal values. The latencies then increased with age, the increase being greater for posterior tibial nerve SEPs than for median nerve SEPs. By contrast, the ascending time (the interval between onset and peak latencies) decreased progressively with age from birth to adolescence.

Adolescent↗
PubMed1986

Somatosensory evoked potentials to posterior tibial nerve stimulation in children.

The somatosensory evoked potentials (SEPs) to stimulation of the tibial nerve were studied in 88 children ranging in age from 1 day to 16 years. SEPs were not evidenced in 10 out of 44 infants less than 1 year old. In others it was a major positive wave (P) with a variable topographic distribution on the midline. The onset and peak latencies of this P were highly variable in different subjects of the same age or body-size, and in the same subject with the active electrode placed in different locations. The lowest values for latency were in subjects about 3 years old. The ascending time of P was the only parameter strictly correlated with age. The results are compared with SEPs to upper limb stimulation, which are constant and more reliable. These results indicate: that the maturation of the peripheral somatosensory pathway proceeds at a faster rate than that of the central somatosensory pathway; that the maturation of the somatosensory pathway of the upper limb precedes that of the lower limb; and that the ascending time of P is a good index of thalamo-cortical maturation. The clinical utility of these SEPs in pediatrics is discussed.

Adolescent↗
PubMed1985

[Maturation of cerebral somatosensory evoked potentials].

Cerebral somatosensory evoked potentials (SEPs) were elicited by stimulation of the median nerve and/or posterior tibial nerve in 117 children of 1 day to 16 years old. A major negative wave (N) was consistently recorded from the parietal region of the scalp when the arm was stimulated. The peak latency, the onset latency, the rising time and the duration of H wave are closely correlated with age and body length. The latencies are shortest in the subjects of 1-3 years old. SEPs to lower extremity stimulation were inconstant in the infants before the age of one. The major positive wave (P) has a variable topographic distribution along the middle line, over the scalp. The latencies are also very variable in the different subjects of the same age as well as in the same subject with different locations of active electrode. Among the parameters studied as for N wave, only the rising time of P wave is significantly correlated with age. The latencies of P wave have the shortest value in the subjects of 1-3 years old. The comparison of SEPs to upper and to lower limb stimulations shows that there is no relationship between them in respect to their morphology and amplitude. The minimum value of the latencies of N and P waves was observed at the same age but the difference between the peak latencies of P and N waves in the same subject increases considerably after 2 years of age and reaches the adult value after 5 years of age. These resultats indicate that the maturation of the peripheral somatosensory pathways proceeds at a higher rate than that of the central somatosensory pathways, that the maturation of the somatosensory pathways of the upper limb precedes that of the lower limb, and that the rising time of N or P waves is a good index of cortical maturation. The clinical utility of these SEPs in pediatrics is discussed.

Adolescent↗
PubMed1985

[Lumbar cord potentials evoked by stimulation of the nerves of the lower limb in man].

Lumbar cord potentials evoked by electrical stimulation of the posterior tibial and sural nerves at the ankle were recorded with monopolar epidural electrodes, at T11-T12 level in 20 subjects and were compared with surface recorded potentials. Two quadriplegic patients with spinal section were included in this group. Curare was given in two cases. Xylocaine block of peripheral nerve was carried out in 4 cases. Double shock study was done in 5 cases. The lumbar cord evoked potentials show two successive components: a 'primary' negative-positive spike response with a latency of 19-35 msec, and the 'secondary' waves with latencies up to 200 msec. The 'primary' response is mainly produced by the afferent volley in the fibres of the dorsal roots and of their intramedullary prolongations. There is no evidence which suggests that it is correlated with presynaptic inhibition. The secondary components may be divided into the early and the late waves. The early waves (40-90 msec) are related to the polysynaptic activities from the afferent fibres of small diameters. The late waves are under the influence of supraspinal mechanism and may be related to long-loop reflexes. The clinical implications of these evoked potentials are discussed.

Adult↗