Is exercise necessary with repetitive nerve stimulation in evaluating patients with suspected myasthenia gravis?

We retrospectively evaluated the effect of exercise on the degree of decrement in ulnar, spinal accessory, and facial repetitive nerve stimulation (RNS) in 179 patients with myasthenia gravis (MG) to assess whether exercise increases the diagnostic yield of identifying significant decrements. The mean worsening of decrement following exercise was 1.9% (ulnar nerve), 1.9% (spinal accessory nerve), and 1.3% (facial nerve). Abnormal (> or =10%) decrement solely following exercise occurred in the ulnar nerve in 7% of patients, accessory nerve in 5%, and facial nerve in 7%. When analyzed according to Myasthenia Gravis Foundation of America class of disease, the likelihood of producing > or =10% decrement only after exercise was greatest in class I MG with facial RNS and in class II and III generalized MG with ulnar and spinal accessory RNS. In all other disease stages, the likelihood of producing > or =10% decrement only after exercise was < or =7%. This study suggests that exercise increases the yield of diagnosis of MG by RNS in only a small percent of patients. Therefore, in most patients with suspected MG, RNS at rest is sufficient and the additional time required for prolonged postexercise RNS may be better spent in examining other muscle-nerve combinations.     

Diagnostic value of double-step nerve stimulation test in patients with Myasthenia Gravis

ObjectiveDouble-step nerve stimulation test (DSST) is a repetitive nerve stimulation (RNS) technique that is performed under exercise and ischemic conditions. We tested the diagnostic significance of DSST at a distal muscle in 17 control subjects and 10 myasthenic patients who had normal conventional RNS test.MethodsMyasthenia Gravis was diagnosed by SFEMG test and acetylcholine receptor antibody titers. During DSST decremental responses were noted. Sensitivity/specificity of DSST were evaluated by receiver operating characteristics (ROC) analysis and best variable in discrimination of myasthenic patients from control subjects with its optimal cutoff-point was selected.ResultsAt a selected cutoff-point, sensitivity and specificity of DSST reached up to 100%. Also DSST response patterns, especially during the resolution of ischemia, showed significant differences in MG patients. There was a delayed recovery in the ischemia–exercise aggravated decremental response after the resolution of ischemia in the patients when compared with rapid recovery in controls.ConclusionsBy using ROC derived cutoff-points, DSST could accurately discriminate MG patients from control subjects. Quantitative results of our study are limited by small series of patients and can vary with larger series. However we think that the difference between the decremental response patterns of patients and controls is a valuable finding.SignificanceDSST can be a sensitive, specific and non-invasive choice in the patients who have high suspicion for MG but normal conventional RNS.     

Single fiber EMG and repetitive stimulation of the same muscle in myasthenia gravis

We performed RNS and SFEMG studies of the same muscle in 46 patients with myasthenia gravis. Maximum decrement to 3–5-Hz stimulation before and after maximum voluntary exercise, percentage of action potential pairs with increased jitter and blocking, and mean MCD in each study were compared. A significant decrement (> 10% decrease in CMAP area or amplitude between the first and fourth response) was never found without increased jitter and impulse blocking on SFEMG. Increased jitter, blocking, and mean MCD were each correlated with maximum decrement (r > 0.61, P < 0.0001). We conclude that decrement to RNS and impulse blocking on SFEMG result from the same physiologic phenomenon, and that SFEMG is more sensitive at detecting disordered neuromuscular transmission given its ability to detect impulse blocking at levels below the resolution of RNS and increased neuromuscular jitter when there is not blocking. © 1994 John Wiley & Sons, Inc.     

Ten-second exercise is superior to 30-second exercise for post-exercise facilitation in diagnosing Lambert-Eaton myasthenic syndrome

An incremental response after brief exercise or high-rate stimulation on the repetitive nerve stimulation (RNS) test is a critical diagnostic criterion for Lambert-Eaton myasthenic syndrome (LEMS). This prospective study was performed to determine what duration of exercise shows the highest diagnostic sensitivity for LEMS. The compound muscle action potential amplitude in the abductor digiti quinti muscle was obtained at rest and after 5 s, 10 s, 15 s, 20 s, 25 s, and 30 s of exercise. Incremental responses were compared for the different exercise durations in 24 studies performed in nine LEMS patients. The increment was highest with 5-s and 10-s exercises (244%-243%) and lowest with 30-s exercise (84%). A gradual decrease in the increment was noted from 5- to 30-s exercise. A significant difference in the increment was noted between 5- to 10-s and 20-s to 30-s exercise. There was significantly higher diagnostic sensitivity with the 10-s exercise compared with 30-s exercise at 100% increment and 60% increment levels. Higher increment and diagnostic sensitivity were achieved with 10-s exercise than with 30-s exercise. Thus, 10-s exercise should be the standard protocol for the RNS test for LEMS.     

Radial nerve repetitive stimulation in myasthenia gravis

The purpose of this study was to compare the diagnostic yield of repetitive radial nerve stimulation (RNS) while recording from extensor indicis proprius (EIP) to other commonly used muscle-nerve combinations in patients with myasthenia gravis (MG). Radial RNS with recording from EIP was performed in 20 controls and 20 patients with MG. It revealed an abnormal decrement at rest in 35% of patients compared to 11% with ulnar nerve stimulation, 64% with spinal accessory nerve stimulation, and 74% with facial nerve stimulation. Radial-EIP RNS is a reliable technique in the evaluation of MG and appears more sensitive than ulnar nerve RNS.     

Muscular fatigue and decremental response to repetitive nerve stimulation in X-linked spinobulbar muscular atrophy

Background and Purpose:  We report decremental responses to repetitive nerve stimulation (RNS) in 11 patients diagnosed with X-linked spinobulbar muscular atrophy (X-SBMA).
Methods:  The compound muscle action potential (CMAP) of the right abductor digiti minimi (ADM) and trapezius (TZ) in response to a 3-Hz stimulation of the ulnar nerve at the wrist and accessory nerve at the neck were recorded by surface electrodes.
Results:  A decremental response to RNS was observed in 90.9% of the TZ muscle and 27.2% in the ADM muscle of patients with X-SBMA.
Conclusion:  These electrophysiological features of X-SBMA are considered to be useful for diagnosis of X-SBMA. Furthermore, the waning phenomena that mostly appeared in the TZ muscle and increment of CMAP in RNS after the exercise also suggest a unique manifestation in X-SBMA.     

THE EFFECT OF PHYSICAL CONDITIONING SUGGESTS ADAPTATION IN PROCOAGULANT AND FIBRINOLYTIC POTENTIAL

Acute exercise evokes a transient increase in procoagulant activity. We evaluated the effect of physical conditioning on the activation of the coagulation and fibrinolytic systems. Two groups of subjects of different aerobic endurance levels (athletes and controls with maximal oxygen uptake (VO_{2 max}) 68,4 and 52,6 ml·kg⁻¹·min⁻¹, respectively), were tested at rest and after standardized exercise at 80 % of their individual VO_{2 max}. There was a significant increase in prothrombinfragment 1+2 (F1+2) level among controls in response to standardized exercise (p<0.05), whereas no significant difference in the level of F1+2 between athletes and controls at rest or in response to exercise was demonstrated. Tissue plasminogen activator (tPA) antigen level at rest was significantly lower in athletes compared to controls (p<0.03). A significant increase was found in the tPA level after standardized exercise in both groups (p<0.02), which was lower in athletes compared to controls (p<0.05). There were no significant differences between athletes and controls in plasminogen activator inhibitor-1 (PAI-1) and thrombin antithrombin complex (TAT) levels at rest. Athletes had a significantly lower PAI-1 level than controls after exercise (p<0.05). In conclusion, the present study suggests an increased activation of the coagulation system in response to exercise in controls only. It also suggests adaptive changes in fibrinolytic potential induced by physical conditioning, as demonstrated by the lower level of tPA at rest and the lower levels of tPA and PAI-1 after exercise in athletes compared to controls. © 1997 Elsevier Science Ltd     

Decremental Responses to Repetitive Nerve Stimulation in X-Linked Bulbospinal Muscular Atrophy

Background and Purpose

X-linked bulbospinal muscular atrophy (X-BSMA) is characterized by bulbar and spinal muscular weakness and fasciculations. Although X-BSMA is a motor neuronopathy, there are several reports of myasthenic symptoms or decremental responses to repetitive nerve stimulation (RNS). We report the results of applying the RNS test to 15 patients among 41 with genetically confirmed X-BSMA; these 15 patients complained of fatigue, ease of becoming tired, or early muscular exhaustion.

Methods

The 3-Hz RNS test was performed on the trapezius, nasalis, orbicularis oculi, flexor carpi ulnaris, and abductor digiti quinti muscles. A decrement greater than 10% was considered abnormal. Additionally, a pharmacologic response to neostigmine was identified in three patients.

Results

A significant decrement was observed in 67% of patients, and was most common in the trapezius muscle (nine cases). The decrement of the trapezius muscle response ranged from 15.9% to 36.9%. The decrement was inversely correlated with the amplitude of compound muscle action potentials at rest. Neostigmine injection markedly improved the decrement in three patients, who showed noticeable decremental responses to 3-Hz RNS.

Conclusions

This study shows that myasthenic symptoms and abnormal decremental responses to low-rate RNS are common in X-BSMA.     

Decremental response of the nasalis and hypothenar muscles in myasthenia gravis

Repetitive nerve stimulation (RNS) is a standard diagnostic procedure in myasthenia gravis (MG). Although RNS sensitivity is highest in weak muscles, RNS is easier to perform in distal muscles that are often not affected. Twenty-five patients with MG were assessed to compare the sensitivity of RNS of the nasalis muscle to that of the hypothenar muscles. Abnormal decrement was found in hypothenar muscles in 9 patients (36%) and in the nasalis muscle in 13 patients (52%). RNS of the nasalis muscle appeared more useful to detect abnormal neuromuscular transmission in patients with oculobulbar MG (5 of 5) than hypothenar RNS (1 of 5). In patients with generalized MG, hypothenar muscles had a similar yield of abnormal RNS tests.     

Masseteric repetitive nerve stimulation in the diagnosis of myasthenia gravis.

OBJECTIVE: (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. METHODS: 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. RESULTS: 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. CONCLUSIONS: Masseteric RNS is a simple and well-tolerated procedure; it offers a new possibility in testing the cranial muscles in disorders of neuromuscular transmission.     

Neuromuscular transmission failure due to common krait (Bungarus caeruleus) envenomation

Neurophysiological studies were performed in 12 patients with neuromuscular paralysis due to envenomation by the common krait (Bungarus caeruleus). All patients presented with an acute, reversible, oculofaciobulbar paresis. In addition, 7 patients had weakness of the limb muscles and 4 required assisted mechanical ventilation. Neurophysiological abnormalities included: (1) a reduction in the amplitude of the median-elicited compound muscle action potential (CMAP) in 4 patients; and (2) a decremental response (>10%) to 3-Hz repetitive nerve stimulation (RNS) in 4 patients. With 1 exception, these abnormalities were noted only in clinically weak muscles. The administration of edrophonium to 6 patients produced an insignificant increase in CMAP amplitudes as well as partial (not significant) improvement in the decremental response to 3-Hz RNS. Neurophysiological studies were performed in 2 patients before and after the administration of 20 mL of polyvalent antivenom. A decrease in amplitude of the median-elicited CMAP amplitude occurred after the administration of antivenom. In 1 patient, administered 100 mL of antivenom, the median-elicited CMAP amplitude increased and the decrement to 3-Hz RNS decreased. Neurophysiological studies can provide useful information regarding the nature, severity, and therapy of the neuroparalytic syndrome of krait envenomation.     

Muscle membrane polarisation after provocative tests, and after cooling: the normal CMAP changes to be expected.

OBJECTIVE: To know the range of changes of compound muscle action potentials (CMAPs) in the muscles innervated by the ulnar nerve after diverse provocative tests, 14 healthy patients were studied with the same protocol. METHODS: CMAPs were measured at rest, just after a short exercise test (SET), during short 5 and 10c/s repetitive nerve stimulation (RNS) trains, at approximately 32 and approximately 20 degrees C. RESULTS: At 32 degrees C, the SET induced a significant but transient enlargement of the CMAPs (amplitude increased by 8.3%, duration decreased by 9%) that was only partially reproduced by RNS trains, except for a significant shortening of the CMAPs at 10c/s. At 20 degrees C without exercise, CMAPs increased significantly by approximately 30% in amplitude, duration and area, and after the SET the inverse of what has been seen at 32 degrees C was observed (amplitude decreased by 1.7% and duration increased by 9%). RNS at 20 degrees C produced a marked interpatient heterogeneity except for a significant shortening of the CMAPs at 10c/s. In one pure autonomic failure patient, the infusion of norepinephrine induced potentiation of the responses at rest and a decrease in the expected changes after provocative tests. CONCLUSIONS: CMAP amplitude and duration are significantly modified just after the SET at 32 degrees C, at rest at 20 degrees C and after RNS at 10c/s but not at 5c/s. Although providing indirect evidence, these findings indicate that provocative tests make the muscle membrane hyperexcitable by the way of a direct influence on the electrical events and by an indirect local catecholamine spillover.     

Trigeminal nerve repetitive stimulation in myasthenia gravis

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.     

New strategy for improving the diagnostic sensitivity of repetitive nerve stimulation in myasthenia gravis

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%; oculobulbar (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. Muscle Nerve 55 : 532–538, 2017     

The accessory nerve repetitive nerve stimulation test: a valuable second-line test in myasthenia gravis

The diagnostic usefulness of the accessory nerve repetitive nerve stimulation (RNS) test was evaluated in 100 patients with myasthenia gravis (MG). The test was easy to perform and reliable at the low rates of stimulation. A higher diagnostic sensitivity was found in the accessory nerve RNS test than in the ulnar nerve RNS test on either the abductor digiti quinti or flexor carpi ulnaris muscles, especially in mild generalized MG. Diagnostic sensitivity was significantly increased when RNS test results for three muscles were combined, especially in mild generalized MG and sero-positive MG. In a small number of cases only the ulnar or accessory nerve RNS test was abnormal. There was a good correlation between electrophysiological and clinical severity of MG in the accessory nerve RNS test Thus, we conclude that the accessory nerve RNS test is a valuable second-line test and its greatest usefulness is in cases of mild generalized MG.     

Repetitive nerve stimulation studies in the Lambert–Eaton myasthenic syndrome

We compared changes in amplitude and area of surface recorded compound motor action potentials (CMAPs) during 20-Hz repetitive nerve stimulation and after maximum voluntary contraction in patients with the Lambert–Eaton myasthenic syndrome (LEMS), myasthenia gravis (MG), and normal controls. There was greater potentiation of CMAP amplitude after voluntary contraction than during 20-Hz stimulation in 10 of 14 LEMS patients; CMAP area increased more after exercise than during 20-Hz stimulation in all LEMS patients. Although abnormal potentiation of CMAP area and amplitude was seen in equal numbers of LEMS patients, more LEMS patients demonstrated a greater than 100% potentiation of CMAP area than of CMAP amplitude. We conclude that maximum voluntary contraction is preferable to brief 20-Hz RNS to demonstrate potentiation in LEMS because it is at least as sensitive and is less painful. Measurement of CMAP area in LEMS patients is not better than measuring the change in CMAP amplitude in demonstrating abnormal potentiation. Testing of a single hand muscle for potentiation in LEMS does not demonstrate abnormal potentiation in all LEMS patients. © 1994 John Wiley & Sons, Inc.     

High-temperature repetitive nerve stimulation in myasthenia gravis

High temperature enhances the decrement on repetitive nerve stimulation (RNS) in patients with myasthenia gravis (MG). However, the limit of this phenomenon at high temperature is unknown. Three-hertz ulnar RNS was performed in 7 patients with MG at a skin temperature of 32°C and then with the hand in a 44°C water bath. At 32°C, the mean decrement preactivation was 5% (range, 0–24%); after 1 min of exercise, the mean decrement reached a maximum of 11% (range, 1–34%) 2 min postactivation. At a hand temperature of 42°C, the mean decrement preactivation was 17% (range, 0–65%); after exercise, the mean decrement reached a maximum of 29% (range, 5–74%) 1 min postactivation. In 3 subjects, RNS was normal at 32°C, but a definite decrement developed with heating. These findings demonstrate that very high temperature can improve the sensitivity of ulnar RNS for postsynaptic neuromuscular transmission defects. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1414–1418, 1998     

Repetitive hypoglossal nerve stimulation in myasthenia gravis.

OBJECTIVES: To assess the diagnostic efficacy of repetitive nerve stimulation (RNS) of the hypoglossal nerve in patients with myasthenia gravis (MG) and bulbar symptoms (dysphagia, dysarthria). METHODS: Twenty patients with MG and 25 normal controls had RNS of the hypoglossal nerve. All patients also had single fibre electromyography (SFEMG) of the orbicularis oculi and RNS with recordings of the nasalis, trapezius and abductor pollicis brevis muscles. RESULTS: All patients had positive SFEMG studies. Nine patients with bulbar symptoms had positive hypoglossal RNS, including 3 with negative RNS recordings in other muscles. Eleven patients with no bulbar symptoms showed negative hypoglossal RNS, including two with positive RNS recordings from other muscles. CONCLUSIONS: Abnormal RNS of the hypoglossal nerve correlates well with bulbar dysfunction and further characterises the extent of neuromuscular transmission defect in MG patients.     

Decrement in area of muscle responses to repetitive nerve stimulation

Measurement of the decremental muscle response to repetitive nerve stimulation (RNS) has low yields for the diagnosis of neuromuscular transmission defects compared with single fiber electromyography (SFEMG). We compared area and amplitude of muscle responses to RNS in 87 patients and 30 controls, using SFEMG as the reference standard. Decrement of response area provided additional diagnostic yields of 5.3% to 30% depending on the muscle examined and disease severity, and is recommended as a diagnostic adjunct to measurement of amplitude decrement during RNS.     

Muscle strength and fatigue in patients with generalized myasthenia gravis

Myasthenia gravis (MG) is characterized by fatigue and fluctuating muscle weakness resulting from impaired neuromuscular transmission (NMT). The objective of this study was to quantify, by direct measurement of muscle force, the strength and fatigue of patients with MG. A maximal voluntary isometric contraction protocol of shoulder abductors was used in conjunction with conventional fatigue and disease‐severity instruments. Results from patients with (D‐MG) and without (ND‐MG) decrement on repetitive nerve stimulation (RNS) of the spinal accessory and axillary nerves were compared with healthy controls. Patients with MG reported greater fatigue than controls. Muscle strength was lowest in the D‐MG group, followed by the ND‐MG group and controls. Normalized shoulder abduction fatigue and recovery values did not differ between the D‐MG and ND‐MG groups or controls. The RNS decrement appears to relate best to disease severity and muscle weakness but not to objective measures of fatigue in this population. Muscle Nerve, 2009