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Trigeminal nerve repetitive stimulation in myasthenia gravis
Abstract
The aim of this study was to evaluate the utility of repetitive nerve stimulation (RNS) of the trigeminal nerve in assessing patients with myasthenia gravis (MG). In 26 normal controls and 21 patients with myasthenia gravis (MG), 2-Hz repetitive stimulation of the trigeminal nerve was performed using a monopolar needle for percutaneous nerve stimulation and recording over the surface of the masseter. In the MG patients, repetitive stimulation of the ulnar, spinal accessory, and facial nerves was also performed. The mean percent decrement in the compound muscle action potential (CMAP) amplitude among the different nerves at rest were: ulnar, 4.3%; spinal accessory, 10.1%; facial, 14%; and trigeminal, 17.3%. The facial nerve demonstrated abnormal decrement in 57% of all patients, compared with the spinal accessory (48%), trigeminal (43%), and ulnar (20%) nerves. All patients tolerated trigeminal RNS better than or as well as facial RNS. The study demonstrates that trigeminal RNS is a safe, reliable, efficient, and well-tolerated technique that provides another cranial nerve-muscle combination that can be used to supplement repetitive stimulation of other limb or cranial nerves in the evaluation of patients with bulbar or generalized MG.
... One of the three tests used for the diagnosis of MG (AChR antibodies, SFEMG, RNS) was abnormal in 99.1% of the patients. Discussion: O.O. is the most sensitive muscle in all groups of MG electrodes, has low sensitivity with a diagnostic yield of 0-62% in ocular and oculobulbar MG [2,7,[11][12][13] . ...
... Only a few studies have correlated RNS sensitivity with MG clinical subgroups [9,10,12,13] . The purpose of this study was to assess the utility of RNS in the O.O., nasalis and ADQ and to correlate the sensitivity of these muscles with the clinical subgroups of MG. ...
... On the other hand, there were no patients, with the exception of one with predominant axial-limb weakness, with positive RNS only in the ADQ. In previous reports, the sensitivity of the hypothenar muscles in generalized MG was 18-37% [11][12][13] , and 62% in only one case [9] . ...
To assess the utility of repetitive nerve stimulation (RNS) in facial and hypothenar muscles in the clinical groups of myasthenia gravis (MG).
We performed RNS study in the orbicularis oculi (O.O.), nasalis and abductor digiti quinti (ADQ) in 115 consecutive myasthenic patients and classified them according to the classifications of the Myasthenia Gravis Foundation of America. Patients were classified into three groups: group 1, group 2 (IIa, IIIa and IVa) and group 3 (IIb, IIIb and IVb).
RNS was abnormal in 95 patients (82.6%): 78.3% in the O.O., 66.1% in the nasalis and 19.1% in the ADQ. Both facial muscles were statistically more sensitive than the ADQ in all groups of patients. RNS in the O.O. was more frequently abnormal than in the nasalis only in group 1. Sensitivity to acetylcholine antibodies in myasthenic patients was 84%. Acetylcholine receptor (AChR) and muscle-specific tyrosine kinase antibodies were present in 96.7% of the patients with abnormal RNS in both facial muscles. Single-fiber electromyogram (SFEMG) was abnormal in 91.3% of the tested patients. One of the three tests used for the diagnosis of MG (AChR antibodies, SFEMG, RNS) was abnormal in 99.1% of the patients.
O.O. is the most sensitive muscle in all groups of MG followed by nasalis, while the ADQ is the muscle with the lowest sensitivity. Facial muscles, especially the O.O., should be the first to be tested in MG. The negativity of all tests (RNS, AChR antibodies, SFEMG) should question the diagnosis of MG, even in the presence of symptoms consistent with MG.
... In bulbar onset MG, stimulation of the hypoglossal nerve while recording from the submental muscle complex [54] is recommended. approaches, which aren't standard, emerge in particular settings, e.g., masseteric nerve stimulation via a monopolar needle in bulbar onset or phrenic nerve RNS in respiratory weakness [58,59]. ...
The diagnosis of autoimmune Myasthenia Gravis (MG) remains clinical and rests on the history and physical findings of fatigable, fluctuating muscle weakness in a specific distribution. Ancillary bedside tests and laboratory methods help confirm the synaptic disorder, define its type and severity, classify MG according to the causative antibodies, and assess the effect of treatment objectively. We present an update on the tests used in the diagnosis and follow-up of MG and the suggested approach for their application.
... In 6% of the myasthenic patients an early fatigue on the masseter muscle occurs, and this muscle is usually involved in most patients in the later period of the disease, with frank weakness and atrophy developing in 15% [18]. Furthermore, the masseter muscle presented the highest degree of abnormality compared to the facial, trapezius, or limb muscles [19][20][21]. Overall, we decided to obtain the control values of the masseter muscle in the SFEMG detection which can be used for further clinical researches. The stimulated jitter values that were obtained in the masseter are similar with the facial muscles, because the masseter resembles most closely in size and length of the fiber, and is similar to the broad studies results [14]. ...
The purpose of this study is to obtain normative values of the masseter muscle of myasthenia gravis (MG) patients and healthy volunteers by single-fiber electromyography (SFEMG). Stimulation of SFEMG in the masseter muscle was studied in 15 healthy volunteers (men 8, women 7; mean age 40.2, range 21-77) and 30 patients affected by MG (men 16, women 14; mean age 42.8, range 12-75). The mean consecutive difference (MCD) of the individual fiber and the mean MCD per study were determined in the normal group. We recommend the upper normal limit for the individual fibers of jitter and the mean MCD per study in the healthy Chinese adults of 33 μs and 22 μs respectively. Furthermore, in the MG group, the percentage of jitter > upper normal limit jitter and the impulse blocking percentage were detected, which were all significantly different compared to the normal control group (P < 0.01). The overall sensitivity was 90%, with the abnormality in 6 of the 9 ocular MG patients and 100% abnormality in the generalized MG patients. The masseter muscle SFEMG has a high degree of sensitivity. The masseter should be considered for SFEMG in the diagnosis of MG, and added routinely to the tested muscles.
... 9,12 Repetitive nerve stimulation disclosed subclinical involvement of the masseter in up to 70% of cases of ocular myasthenia 13 ; furthermore, this muscle exhibited the highest degree of abnormality as compared with trapezius, facial, or limb muscles. 2,13,14 The motor portion of the mandibular nerve is rarely affected by neuropathies, 7 so the masseter is unlikely to yield false-positive results. Considering also the easy accessibility of the masseter, we decided to obtain control values using a technique based strictly on well-established guidelines for stimulated jitter. ...
Jitter after axonal microstimulation in the masseter muscle was studied in 30 consecutive patients (12 women) with myasthenia gravis (MG). Patients' mean age was 42.3 (12-75), median disease duration was 3 months (1-72), and onset was ocular (15 cases), oculobulbar (7), bulbar (6), or generalized (2). There were 23 newly-diagnosed patients. Nine cases developed purely ocular MG and 21 cases developed generalized MG. In the latter group, five subjects had a rapidly progressive course and 16 subjects had stable or well-controlled disease (MGFA grade 2-3). Six patients did not have circulating anti-acetylcholine receptor antibodies. Masseter single-fiber electromyography (SFEMG) was abnormal in 6 of 9 ocular MG patients and in all generalized cases (overall sensitivity 27 of 30 cases or 90%; confidence interval 79.3%-100.0% at P = 0.95). Masseter should be considered for SFEMG in diagnosis of MG, especially in cases with bulbar onset.
Introduction:
We aimed to evaluate the reliability and reproducibility of repetitive nerve stimulation (RNS) recorded on occipitalis muscle by comparing recordings on nasalis muscle in healthy subjects.
Subjects:
and methods: A total of 23 healthy subjects (mean age: 44.7±13.8 years) underwent detailed neurological examination and RNS using nasalis and occipitalis muscles. Amplitude and area percentage changes of CMAPs after RNS with different frequency were compared between right and left-sides and between recordings on nasalis and occipitalis muscles.
Results:
Comparisons of percentage amplitude changes of nasalis and occipitalis CMAPs showed no differences (+0.1±3.8% vs +1.4±3.9%, p=0.129). Average area percentage change of nasalis CMAPs was 0.3±19.0% whereas the value of occipitalis CMAP was +2.8±15.2% (p=0.851). Comparisons of nasalis and occipitalis CMAPs values showed no differences.
Conclusion:
The RNS recorded on occipitalis muscle is simple, easy to apply, noninvasive, consistent and reproducible.
Introduction:
The diagnostic sensitivity of repetitive nerve stimulation (RNS) in patients with myasthenia gravis (MG) varies as a function of the number of muscles or the choice of muscles studied.
Methods:
By exploring 12 muscles bilaterally, we evaluated the global sensitivity of RNS at rest, the sensitivity in different clinical forms, and the sensitivity of different combinations of muscles studied.
Results:
The global sensitivity of RNS was 82%, and specificity was 100%. The sensitivity in the MG subgroups was as follows: ocular (O) = 67%, oculo-bulbar (OB) = 86%, and generalized (G) = 89%. The most sensitive muscles were the anconeus in group O, orbicularis oculi (OO) or nasalis in group OB, and the trapezius in group G. Maximum sensitivity was obtained by exploring OO, trapezius, and anconeus bilaterally.
Conclusions:
We recommend bilateral exploration of at least 3 muscles: a facial muscle, trapezius, and anconeus. This article is protected by copyright. All rights reserved.
Provide an updated literature review of electrodiagnostic testing in myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS).
A systematic review of the recent literature was performed using key words: myasthenia gravis (MG), Lambert Eaton myasthenic syndrome (LEMS), electromyography (EMG), repetitive nerve stimulation (RNS), single fiber electromyography (SFEMG), nerve conduction study, normative values.
Several articles supported testing of facial, bulbar, and respiratory muscles in the diagnosis of neuromuscular junction (NMJ) disorders, including MuSK seropositive MG. Several articles supported use of concentric needle EMG as an alternative to SFEMG jitter in disorders of neuromuscular transmission. A limited number of articles concerned measurement of area (vs. amplitude) decrement in RNS and decreasing the threshold of post-exercise facilitation.
Electrodiagnostic testing continues to be useful for diagnosis of MG and LEMS, though the quality of the evidence is not great. This literature review summarizes RNS and jitter measurement to facial and respiratory muscles and use of concentric needle EMG for SFEMG. This article is protected by copyright. All rights reserved.
© 2015 Wiley Periodicals, Inc.
This article reviews in-depth the technique of repetitive nerve stimulation in the diagnosis of neuromuscular transmission disorders. A decrement in amplitude from the first to fourth compound muscle action potential of at least 9% while stimulating at low-frequency (up to 5 Hz) is valid for the diagnosis of neuromuscular transmission disorders. Technical pitfalls include: (1) No supramaximal nerve stimulation (2) Motion artifacts (3) Shifting the stimulating electrode during stimulation, which can easily mimic a pathological decrement. (4) No temperature control. The degree of decrement is lower in cold extremities. (5) Testing should be performed with patient free of all cholinesterase-inhibitor medications, like pyridostigmine. (6) Investigation of non-affected muscles. Repetitive nerve stimulation results fluctuate with the severity of weakness (e.g. testing in the early morning versus late afternoon). Additional serial testing during the so-called post-tetanic exhaustion phase increases the diagnostic sensitivity. A pathological decremental response can occur in a variety of neuromuscular disorders.
The purpose of our study was to show neuromuscular transmission abnormality in the masseter muscle of generalised myasthenia gravis (MG) patients and to compare motor end-plate failure of the masseter with the extensor digitorum communis (EDC) and periocular muscles.
Motor end-plate function was evaluated during voluntary contraction of the masseter muscle of 20 generalised MG patients aged between 16 and 63years, as well as 20 age-matched healthy volunteers. The mean jitter value was calculated for each group and compared. The upper limit of normal jitter was also calculated and the number of jitters exceeding this cut-off value was counted for each group for comparison. In MG patients, jitter analysis was also performed in periocular and EDC muscles along with the masseter and the number of single fibre-like potentials with abnormal jitter was counted for each muscle. All tests were performed during the same session with a concentric needle electrode (CNE).
For the masseter muscle, the mean jitter of all potential pairs was significantly higher in the patient group (24.7±9.6μs in healthy volunteers, 71.9±41μs in patients). The calculated mean jitter for the 18th highest value in healthy volunteers was 33.8±5.9μs (upper 95% confidence limit was 45.6μs). The number of abnormal jitters (⩾46μs) was significantly higher in the patient group (276 out of 402 jitters) compared to healthy volunteers (10 out of 400 jitters). In the patient group, the number of single fibre-like potentials with abnormal jitter was found to be similar for the masseter, periocular and EDC muscles.
The masseter muscle has diagnostic importance in generalised MG. The ratio of high jitters to all of the calculated jitters in a particular muscle was similar for masseter, periocular and EDC muscles.
Jitter analysis of the masseter muscle during voluntary contraction is easy to perform and it was found as informative as other muscles in patients with generalised MG.
Le diagnostic d'une myasthenie est avant tout clinique, mais il est aide par l'electroneuromyographie (ENMG) et la biologie. L'examen ENMG est facilement disponible et son resultat est immediat. Il est utile devant des symptomes frustres, mais aussi devant des tableaux plus aigus de deficit moteur generalise, de troubles bulbaires ou respiratoires. Il peut etre realise en ambulatoire ou au lit du malade. L'ENMG repose sur l'evaluation des stimulations repetitives qui peuvent etre sensibilisees et plus rarement sur l'etude du jitter lors de l'examen en fibre unique. Les stimulations repetitives monosalve multisites adaptees a la symptomatologie sont a privilegier. L'interet de ces tests est variable selon les situations cliniques non seulement pour le diagnostic mais aussi au cours de l'evolution, pour objectiver concretement les effets d'un traitement.
This chapter explains the diagnostic applications of neurophysiological methods in disease rather than on the methods themselves, it includes a short technical section on the trigeminal evoked potentials after electrical or laser stimuli. Neurophysiological findings in patients with trigeminal lesions, craniofacial pains, and facial, accessory, and hypoglossal neuropathies have been discussed in detail. This chapter also deals with the cranial nerve involvement in systemic or extra-segmentary diseases such as polyneuropathy, motor neuron disease, and myasthenia. However, in the cranial nerve territory, motor function is assessed with transcranial magnetic stimulation and electrical stimulation of the extra-cranial nerve branches, sensory function with trigeminal-reflex techniques.
This article is a general review of cranial nerve conduction studies, including techniques as well as interpretation of data. The needle examination of various cranial innervated muscles is also reviewed. The nerve conduction studies include the blink, masseter (jaw jerk), and masseter inhibitory reflexes, which evaluate the trigeminal (blink and jaw jerk) and facial nerves (blink), as well as trigeminal, facial, and spinal accessory motor stimulation. The needle examination techniques for certain voluntary muscles innervated by cranial nerves V, VII, X, XI, and XII are also described.
Neuromuscular junction (NMJ) disorders may be demonstrated using repetitive nerve stimulation (RNS) testing and single-fiber electromyography (SFEMG). RNS testing with low frequency stimulation reduces the safety factor of neuromuscular transmission (NMT) and may elicit decrementing compound muscle action potential (CMAP) responses. Exercise or tetanic nerve stimulation may potentiate acetylcholine release in presynaptic NMT disorders with CMAP facilitation. SFEMG is a selective recording technique assessing MFAPs within the same motor unit. Jitter is increased in NMJ disorders, and is the temporal variability between these MFAPs. Impulse blocking reflects failure of NMT. RNS and SFEMG findings in NMJ disorders are reviewed.
The aim of this study was to elucidate the relationship between the impairment of excitation-contraction (E-C) coupling and anti-ryanodine receptor (RyR) antibody in patients with myasthenia gravis (MG).
Masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRPs) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated as the latency difference between CMAP and MRP. For each patient, we selected a representative data set when there was no abnormal decrement in response to repetitive nerve stimulation. The 26 data sets were divided into an anti-RyR-positive group (n=12) and an anti-RyR-negative group (n=14).
Masseteric ECCT was significantly longer (p=0.017) in anti-RyR-positive group (median, mean, range; 3.6, 3.8, 3.0-5.9 ms) than in anti-RyR-negative group (3.1, 3.1, 2.7-4.0) although there were no significant differences in masseteric CMAP amplitude and % decrement between the two groups. The bite force was significantly lower in anti-RyR-positive group than in normal controls.
Presence of anti-RyR antibodies is associated with significantly prolonged masseteric ECCT compared to absence of the antibodies in MG.
Anti-RyR antibody contributes to E-C coupling impairment in the masseter muscle in patients with MG.
The aim of this study was to elucidate the relationship between the impairment of excitation-contraction (E-C) coupling of masseter and the bite force in patients with myasthenia gravis (MG).
In 20 patients with MG, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRP) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Serial assessments of % decrement in masseteric repetitive nerve stimulation (RNS), ECCT, and bite force were performed before and after corticosteroid therapy alone or in various combinations with FK506, cyclosporin A, intravenous immunoglobulin and immunoabsorption.
Percent amplitude decrement in RNS and ECCT decreased significantly accompanying an increase in bite force after treatment. Simple regression analysis demonstrated a linear correlation among % decrement, ECCT and bite force. However, ECCT shortening accompanying bite force recovery without reduction in % decrement was observed in 4 patients.
Masseteric E-C coupling is impaired in some MG patients, and functional recovery of E-C coupling contributes at least in part to the increase in bite force after treatment.
Impaired E-C coupling contributes to muscle weakness in patients with MG.
We performed a systematic review to identify studies that reported the accuracy of tests for the diagnosis of myasthenia gravis. We identified 20 studies of reasonable, although variable, methodological quality upon which to base estimates of the accuracy of the ice test, rest test, Tensilon test, acetylcholine receptor antibodies, repetitive nerve stimulation and single fiber electromyography for the diagnosis of myasthenia gravis. After examining inter-study heterogeneity for each diagnostic modality, we calculated pooled estimates of sensitivity and specificity as well as positive and negative likelihood ratios. Results are reported separately for ocular and generalized myasthenia. Studies that have examined the performance of anti-acetylcholine receptor antibody testing and single fiber electromyography were generally of better quality than those that examined other diagnostic modalities. We suggest that caution should be exercised in the interpretation of the diagnostic performance of these tests given the methodological limitations of the studies upon which test performance is based.
Cranial nerve abnormalities occur frequently in both focal and diffuse neurologic disorders and can be evaluated by electrophysiological techniques available in most clinical neurophysiology laboratories.
The optic nerve is evaluated by visual evoked potentials. Measurements of latency, amplitude, and waveform morphology are especially useful in detecting demyelinating lesions. Brain stem auditory evoked potentials evaluate the auditory portion of the eighth cranial nerve. Using an auditory stimulus, a number of waveforms are generated, and changes in the normal patterns of response can detect abnormalities. Assessment of the trigeminal and facial nerves is done using a series of electrical stimulation techniques including the blink, masseter, and masseter inhibitory reflexes and facial motor nerve conduction studies. The blink reflex detects lesions of the first division of the trigeminal nerve and the facial nerve. The masseter reflex evaluates the third division of the trigeminal nerve. Changes in responses are measured and, using a combination of these techniques, localization of lesions at specific sites can be made. Accessory motor nerve conduction is useful not only in focal nerve injury, but repetitive stimulation on the accessory and facial nerves is used in diagnosing neuromuscular junction disorders. In addition, many of the voluntary muscles innervated by the cranial nerves are accessible to needle electrode examination, and evaluation can aid in identification of focal nerve lesions, as well as diagnosis in diffuse nerve and muscle disorders.
Electrophysiological techniques offer reliable means of measuring the integrity of the cranial nerves and their central pathways.
Nineteen healthy volunteers (median age, 25; range, 18-51 years) were enrolled in a study to obtain normative values for stimulated jitter in the masseter muscle. Axonal microstimulation was performed via a monopolar needle electrode introduced in the masseter 2-2.5 cm above the mandibular angle on the line connecting it with the lateral canthus. The recording single-fiber electromyography (SFEMG) electrode was inserted anteriorly in the twitching area of the muscle. The mean consecutive difference (MCD) values for the 426 endplates studied followed a distribution skewed to the left, with a minimum value of 4.3 micros, maximal 44.7 micros, and a maximum of distribution at 11 micros. Mean pooled MCD measured 16.0 micros, and the mean of mean MCD per study was 13.6 micros. The value of the 95th upper percentile for an individual fiber was 29.3 micros. We suggest an upper normal limit for mean MCD per study of 21 micros and upper normal limit of MCD for individual fibers of 30 micros. The stimulated jitter study of masseter muscle is easy and reliable.
CMAPs are among the most helpful recordings in the electrophysiologic assessment of peripheral neuromuscular disease. Compound muscle action potentials are the recordings made for all motor conduction studies, both of the directly recorded M wave used for peripheral conduction and the F-wave late response used for testing proximal conduction. Reliable CMAP recordings require the use of standard stimulating and recording electrode types and locations and standard measurement criteria. ¹¹⁵ The sensitivity and specificity of motor conduction studies depend on comparing the results obtained in a patient with the normal values obtained by using exactly the same methods. The normal values of motor conduction studies vary with physiologic factors such as age and temperature, which must be controlled and adjusted.
A prospective multicenter study on the incidence of myasthenia gravis (MG) based on 2,924,710 people was performed from 1993 to 1994. The crude annual incidence rate of new diagnoses was 14.7:1,000,000. This study emphasizes the importance of a prospective multicenter approach in evaluating the true frequency of the disease.
A retrospective literature review of the electrodiagnosis of myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) through July 1998 was performed for the purpose of generating evidence-based practice parameters. There were 545 articles identified, of which 13 articles met at least three of the six criteria set previously by the American Association of Electrodiagnostic Medicine (AAEM). An additional 21 articles were identified from review articles or the references of these first 13 articles leading to a total of 34 articles. Results of studies utilizing repetitive nerve stimulation (RNS) showed that a 10% decrement in amplitude from the first to fourth or fifth intravolley waveform while stimulating at 2-5 Hz is valid for the diagnosis of MG. The degree of increment needed for the diagnosis of LEMS is at least 25% but most accurate when greater than 100%. Abnormal jitter or impulse blocking are the appropriate criteria for diagnosis of neuromuscular junction (NMJ) disorders when using single fiber electromyography (SFEMG). SFEMG is more sensitive than RNS for the diagnosis of disorders of neuromuscular transmission, but may be less specific and may not be available. Therefore, RNS remains the preferred initial test for MG and LEMS.
Two hundred and fifty consecutive patients were evaluated for myasthenia gravis with repetitive supramaximal stimulation of peripheral nerves and regional curare administration when necessary. Among patients with definite generalized myasthenia gravis, 72 percent had abnormal responses to repetitive supramaximal stimulation alone and another 17 percent had abnormal responses after regional curare administration. Among those with possible generalized myasthenia gravis, 15 percent had abnormal responses to repetitive supramaximal stimulation and another 12 percent had abnormal responses after regional curare administration. Of those with only ocular symptoms, 46 percent had abnormal responses to repetitive supramaximal stimulation before or after regional curare administration, suggesting generalized involvement. Myasthenia gravis has not developed subsequently in any of the equivocal patients with negative electric tests. We have found these electric procedures to be simple, safe, and at least as effective as other methods in diagnosing myasthenia gravis.
Myasthenia gravis is a neuromuscular disease of insidious onset, characterized by weakness and fatigability of voluntary muscles. Most patients present with symptoms relating to the head and neck and thus may be seen first by the otolaryngologist. Predominant symptoms may be ocular (ptosis or diplopia) or related to fatigue of the oropharyngeal or laryngeal musculature (dysarthria, dysphonia, or dysphagia). Alleviation of muscular weakness and fatigability after administration of anticholinesterase drugs is pathognomonic of myasthenia gravis.
The purpose of this study was to derive numerical data concerning the probability of diagnosing myasthenia gravis by electrical tests, employing repetitive stimulation of motor nerves. This was done by recording the compound muscle action potential (CMAP) from 80 patients with clear-cut myasthenia gravis, using a number of different, reportedly useful, testing techniques. In 95% of these patients, the diagnosis could be documented by the careful application of rather simple methods, providing several muscles, including a proximal one such as deltoid, were studied.
The diagnostic sensitivity of three laboratory tests [serum antiacetylcholine receptor antibody (AChR-ab) assay, the repetitive nerve stimulation (RNS) test, and, the single fiber EMG (SFEMG)] for myasthenia gravis (MG) was compared in 120 patients. In all cases, at least one of the tests was abnormal. SFEMG was the most sensitive test, being abnormal in 92% of cases, followed by the RNS test (77%) and the AChR-ab assay (73%). SFEMG was abnormal in all cases with negative AChR-ab and RNS tests, in 97% of cases with negative AChR-ab assay, in 89% of cases with negative RNS test, and in 89% of cases with mild MG. We conclude that one of these three tests is abnormal in all cases of MG, and that the SFEMG is most sensitive in the diagnosis of MG.
Effective diagnostic methods are of great importance in order to recognise myasthenic patients among those with muscle fatigability. Intracellular recordings are useful for research work within the field and for detailed description of the motor end-plate's physiology in the individual case. The method is not used for the routine diagnosis of myasthenia gravis. The decrement of the electrical muscle response with nerve stimulation is the most commonly used method. The diagnostic yield is higher in proximal muscles, in warmed muscles, after exercise, and after ischaemia. A significant number of patients may be undiagnosed with this technique. The mechanical response with nerve stimulation shows the same type of decrement but also an abnormal response to long stimulation. The diagnostic value of this is under dispute. Single fibre ENG needs more patient cooperation than do these tests. The diagnostic yield is significantly higher. Some patients considered to have myasthenia gravis do not show any abnormalities with this technique, particularly those with the pure ocular form. Conventional EMG is not useful for the diagnosis of myasthenia, but may be indicated in these patients when concurrent nerve or muscle disease is in question. Tests for eye movement fatique have not proved useful. Stapedius reflex fatigability is demonstrated in about the same proportion of patients as have positive SFEMG findings. The technique is not uncomfortable for the patient and requires minimal cooperation. The general usefulness must be assessed by further routine use. Even with the advent of immunological tests, neurophysiological investigations are indispensable in helping establish the diagnosis of myasthenia gravis. Discrepancies between the results comparing electrophysiological and immunological tests may indicate that myasthenia gravis is a heterogenous entity within which subgroups may be identified.
Results of the electromyography (E.M.G.), automatic analysis of the voluntary pattern, and repetitive nerve stimulation, in 34 patients with myasthenia gravis (M.G.), are described. Classical repititive nerve stimulation at warmed hand muscles only shows significant decrement of the response in 64% of the patients. Diagnostic yield increases to 79% when proximal muscles are tested or provocative test under ischaemia is performed. The 'myopathic' pattern found in conventional E.M.G. study and the results of automatic analysis of the voluntary pattern are discussed.
Repetitive nerve stimulation testing of the ulnar nerve was systematically performed on 21 normal controls and 120 patients with myasthenia (MG). Diagnostic sensitivity increased from 0% in MG in remission and 17.2% in ocular MG to 100% in severe generalized MG. Six types of responses were observed in MG and could be classified into two distinct patterns based upon disease severity: (1) in mild MG, an abnormal decremental response at low rate of stimulation, normal response at high rate of stimulation, and prominent posttetanic facilitation and exhaustion phenomena; and (2) in severe MG, abnormal decremental responses at low as well as high stimulation rates and less common posttetanic facilitation and rare posttetanic exhaustion phenomena. This difference is most likely due to the severity of the neuromuscular block in MG.
(1) to develop a method for masseteric repetitive nerve stimulation (RNS) and to obtain normative data for amplitude and area decrement of the muscle (M) response. (2) To investigate myasthenia gravis (MG) patients with masseteric RNS. Masticatory muscles are frequently affected in MG, but no RNS test is available to investigate this district.
Fifteen healthy subjects and 17 MG patients were examined. The masseteric nerve was stimulated by a monopolar needle (cathode), inserted between the mandibular incisure and the zygomatic arch, and a surface electrode (anode), on the contralateral cheek. Masseteric M response was recorded using surface electrodes on the muscle belly and below the mandibular angle. Stimuli were delivered at 3 Hz in trains of 9, at rest and after isometric effort.
Normal subjects: mean amplitude decrement was 0.3+/-1.2% at rest, and 1.9+/-1.3% after isometric effort. Patients: 15 patients (88%) were positive on masseteric RNS; in 3 of these it was the only positive RNS test. The extent of decrement observed in masseter muscle was significantly greater than in trapezius muscle.
Masseteric RNS is a simple and well-tolerated procedure; it offers a new possibility in testing the cranial muscles in disorders of neuromuscular transmission.
Study Group on Clinical and Epidemiologi-cal Problems in Neurology Incidence of myasthenia gravis in the Emilia-Romagna region: a prospective multicenter study
- Emilia
Emilia-Romagna Study Group on Clinical and Epidemiologi-cal Problems in Neurology. Incidence of myasthenia gravis in the Emilia-Romagna region: a prospective multicenter study. Neurology 1998;51:255–258.
New diagnostic procedures in myasthenia gravis In: editor. New developments in electromyography and clinical neurophysiology
- Borenstein