Key Words: Myasthenia Gravis -- submaximal stimulation. Introduction. Stimulation .... the Lambert-Eaton myasthenic syndrome [9]; moreover, activation of all the ...
Ital. Z Neurol. Sci. 12:565-568, 1991
Submaximal nerve stimulation with the Datex relaxograph NMT monitor in myasthenia gravis Fiacchino F., Gemma M., Bricchi M., Ferrazza C., Regi R, Scaioli V., Montolivo M. Istituto Neurologico Nazionale "C. Besta" Milano
Recently submaximal train-of-four stimulation of motor nerves has been reported as a reliable technique for monitoring the neuromuscular function in patients awakening from anaesthesia, in order to prevent residual curarization. On the basis of the similarity between curarization and Myasthenia Gravis, we studied the neuromuscular impairment offour myasthenic patients by means of a commercially available monitor, which has been designed for routine application in the operating room. We demonstrate that the cardinalfeatures of Myasthenia Gravis can be easily detected with this simple and painless method.
Key Words: Myasthenia Gravis - - submaximal stimulation
Introduction Stimulation with submaximal current for train of four (TO F) monitoring of residual curarization in awake patients has been recently reported to be a reliable procedure [1, 2]. The similarity between the decremental response caused by non-depolarizing muscle relaxants and that caused by anti-acetylcholine-receptor antibodies is such that, from a neurophysiological point of view, curarization [3] and Myasthenia Gravis (MG) [4] are both assessed by the same diagnostic technique. Post-activation facilitation and exhaustion, increased decrement with temperature, sensitivity to the Edrophonium test and unequal distribution of decrement between proximal and distal muscles are the cardinal features of the neuromuscular impairment occurring in MG [4]. We report clinical observations which indicate that the cardinal features of neuromuscular impairment occurring in MG may be easily detected by the use of submaximal (and painless) stimReceived t5 May 1990- Accepted 30 June 1991
ulation with a monitor that has been designed for routine application in the operating room.
Patients and methods Four female myasthenic patients about to be dismissed from the Intensive Care Unit had been scheduled for a second electromyographic examination with a Medelec MS 92 A equipment to compare the myasthenic decrement observed on admission with that occurring after clinical improvement. When the supramaximal stimulation with the Medelec equipment was completed, submaximal stimulation was started with one or two Datex Relaxograph NMT monitors [5]. Patients were fully cohoperative and informed about the procedure. They were requested to assume and maintain the most comfortable position (the arm that was tested was not immobilized) and to advise the examiner about any unpleasant feeling during stimulation. 565
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TABLE I. Fade observed with the Medelec equipmentjust before starting the test with the Date.,: Relaxograph. .....
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Supramaximal stimulation Abd. Dig. Muscle
Trapezlus Muscle
25% 4% 16% 12%
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Results A good correlation was observed in the decrement obtained with supra-- and submaximal stimulations (Table I). The examination was quite well tolerated by all the patients. Fig. I refers to a positive Edrophoniam test (6) performed in a 58-yr-old patient hay-
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Fig. 1. Abductor digiti minimi. Mark 1: Edrophonium (2 mg i.v.) Stim.: 25 mA TOF interval: 20 s.
Fig. 2. Left abductor digiti minimi (lower recording) has no decrement while a decrement of 30% is present on the left trapezius (upper recording) 10 min later. Stim.: 30 mA. TOF interval: 20 s.
We used stimulations at 25-30 mA because, according to our experience with the Datex Relaxograph [2], these amperages are quite well tolerated by most awake patients. When assessing the post-activation facilitation and exhaustion the patient was instructed to spread his little finger out away from the others as strongly as possible while the examiner was giving resistance at the proximal phalanx of the fifth digit in the direction of adduction for 10-15 seeonds. TOF submaximal stimulis were delivered to the accessory and/or ulnar nerves every 10 or 20 seconds. The decrement was displayed as the ratio between the fourth and the first response in each TOF. When the printer was used with the "fast speed", every response of the TOF was recorded; when used with the "slow speed", only the first and fourth responses were recorded.
ing a decrement of approximately 20% on the abductor digiti minimi. Fig. 2 refers to a 38-yr-old patient having no decrement at all on the left abductor digiti minimi (lower recording) and a decrement of approximately 30% on the left trapezius (upper recording). Fig. 3 refers to a 36-yr-old patient in whom postactivation facilitation and exhaustion were evaluated twice on the right abductor digiti minimi with a time interval of approximately 300 minutes. Fig. 4 refers to a 22-yr-old patient in whome a simultaneous monitoring of the abductor digiti minimi ofthe fight and left hands was performed. A few minutes after calibration an infrared lamp was positioned over the fight arm and the effect of maximal abduction of the fifth digit was assessed simultaneously on both sides after removing the infrared lamp.
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Fiacchino E: Submaximal nerve stimulation in myasthenia
Fig. 3. Abductor digiti minimL
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Discussion The reduction of the safety margin of neuromuscular transmission has been compared to an "iceberg" which can be detected by low-frequency stimulation of the motor nerve [7]. Low-frequency is recommended to avoid the summation of facilitatory effects produced by the entry of caldum ions into the nerve terminal with each nerve action potential of a train [8]. Supramaximal stimulation is recommended for two main reasons: the amplitude of the first muscle potential in a train may be relevant in assessing whether the decrement obtained with low-
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frequency stimulation is attributable to MG or to the Lambert-Eaton myasthenic syndrome [9]; moreover, activation of all the nerve fibers is a necessary prerequisite if the decremental response of a muscle has to be compared in subsequent examinations. But, so far as the detection of the "iceberg" is concerned, the decrement observed in a group of muscle fibers and that observed in all the fibers of the same muscle should be regarded as equally important. Both decrements, in fact, indicate that neuromuscular transmission is impaired, but neither is sufficient, in itself, to demonstrate that the impairment is occurring with the same features in differ-
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ing from abductor digiti minimi of the left (lower recording) and right (upper) hands. Mark I: an infrared lamp is positioned over the right arm. Mark 2: the lamp is removed. Mark 3: forced abduction of fingers of both hands. Stim.: 30 mA. TOF interval: 20 s.
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Italian Journal of Neurological Sciences
ent muscles o f the same patient [4, 10]. Difficulties in maintaining a constant activation o f the same subgroup o f nerve fibers may occasionally be encountered when submaximal stimulation is used. A more appropriate positioning and immobilizzation o f the surface electrodes
may be o f value in these circumstances. We think, however, that in most circumstances submaximal stimulation with the Datex Relaxograph is a reliable, useful and quite well tolerated procedure to ascertain the occurrence o f a myasthenic defect.
Sommario
Recentemente la stimolazione submassimale con stimoli tipo "train-of-four " dei nervi motori b stata indicata come una valida tecnica di monitoraggio della funzione neuromuscolare del paziente in risveglio dall'anestesia per individuare eventuali curarizzazioni residue. Sulla base delle somiglianze fra curarizzazione e Miastenia Gravis abbiamo studiato la compromissione neuromuscolare di quattro pazienti miasteniche mediante l'uso di un monitor attualmente in commercio per l'uso in sala operatoria. Dirnostriamo che le caratteristiche principali della Miastenia Gravis possono esserefacilmente individuate con questa tecnica semplice e indolore.
Address reprint requests to: Dr. Folco Fiacchino Istituto Nazionale Neurologico "C. Besta" Via Celoria 11 - 20133 Milano
References
[1] BRULLS.J., EHRENWERTHJ., SILVERMAND.G.: Stimulation with submaximal currentfor Train-ofFour monitoring. Anesthesiology 72:629-632, 1990. [2] FIACCHINO F., BRICCHI M., MONTOLIVO M., FERRAZZAC., BORRONIV. : Assessment of the Datex Relaxograph in accessory nervestimulation (Letter to the Editor) Br., J., Anaesth. 61:238-239, 1988. [3] A u H.H.,SAVARESEJ.J.: Monitoring of neuromuscularfunction. Anesthesiology 45:216-249, 1976, [4] STALBERGE.: Clinical electrophysiology in Myasthenia Gravis. J. Neurol. Neurosurg. Psychiatry 43:622-633, ! 980. [5] CARTER J.A., ARNOLD R., YATE P.M., FLYNN P.J.: Assessment of the Datex Relaxograph during anaesthesia and atracurium-induced neuromuscular blockade. Br. J. Anaesth. 58:1447-1452, 1986. [6] OSSERMANK.E., GENKINSG.: Studies in Myastbenia Gravis: review of twenty-year experience in
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over 1200 patients. The Mount Sinai J. Med. 38:497-537, 1971. [7] WAUDB.E., WAUDD.R.: Phisiology andpharmacoiogy of neuromuscular blocking agents, Muscle Relaxants. Edited by Katz R.L., Amsterdam, London, New York. Excerpta Medica, American Elsevier, 1975, pp. 1-58. [8] DESMEDTJ.E., : Presynaptic mechanism in Myasthenia Gravis. Ann. N. Y. Acad. Sci. 135:209-246, 1966. [9] LAMBERT E.H., ROOKE E.D,. EATON L.M., HODGSONC,H.: Myasthenic syndrome occasionally associated with bronchial neoplasm: neurophysiologic studies, Myasthenia Gravis. Edited by Vietes H.R., Springfield, Illinois, Chades Thomas, 1961, pp. 362-41. [10] DE TROVERA., BASTENmRJ., DELHEZ L.: Function of respiratory muscles during partial curarization in humans. J. Appi. physiol. 6:1049-156, 1980.
