Abnormal Jitter Research Articles

Single‐fiber electromyography shows terminal axon dysfunction in Miller Fisher syndrome: A case report

We studied a patient with ophthalmoparesis and pupillary areflexia 2 weeks after a viral syndrome. Miller Fisher syndrome was suspected but GQ1b antibodies were not detected. To define neuromuscular involvement we performed electrodiagnostic studies. Single-fiber electromyography (SFEMG) in the extensor digitorum communis (EDC) showed abnormal jitter and axonal blocking, suggesting terminal axon dysfunction. Subsequent GQ1b antibody titers were elevated to borderline levels. Clinical symptoms gradually resolved. SFEMG may help characterize neuropathies associated with antibodies to neuronal ganglioside and identify involvement of the terminal axon and neuromuscular junction.

Single‐fiber electromyography in limb and facial muscles in muscle‐specific kinase antibody and acetylcholine receptor antibody myasthenia gravis

We examined the findings from single-fiber electromyography in extensor digitorum communis (EDC) and orbicularis oculi (OOc) in 13 myasthenia gravis (MG) patients with muscle-specific kinase antibodies (MuSK-MG) and 12 MG patients with acetylcholine receptor antibodies (AChR-MG) with similar clinical scores. More than 70% of AChR-MG patients had abnormal jitter in both EDC and OOc, but the majority of MuSK-MG patients had normal jitter in EDC despite abnormal jitter in OOc. These findings demonstrate clear differences between the neurophysiology of MuSK-MG and AChR-MG.

MuSK-antibody positive myasthenia gravis: Clinical and electrodiagnostic patterns

Objective To examine the clinical manifestations and patterns of electromyographic abnormalities in MuSK-Ab positive myasthenia gravis. Methods The clinical evaluations and electrodiagnostic testing results of 20 MuSK-Ab positive myasthenia gravis patients were retrospectively reviewed and compared with matched AChR-Ab positive ( N=72) and MuSK-Ab negative/AChR-Ab negative ( N=24) patients. Results MuSK-Ab positive patients were younger and more frequently female and African-American, and compared to the AChR-Ab positive patients, were more likely to present with respiratory symptoms or neck extension weakness. MuSK-Ab positive patients were less likely to have abnormal jitter in a limb muscle: only 59% had abnormal jitter in the extensor digitorum communis muscle, compared to 80% of the AChR-Ab negative/MuSK-negative patients and 91% of the AChR-Ab positive patients. Conclusions Our MuSK-Ab positive patients not only differ demographically from our MuSK-Ab negative cohort, but they also appear to have a more limited distribution of SFEMG abnormalities. Significance The possibility that electrophysiologic abnormalities may not be widely distributed should be considered during electrodiagnostic evaluation of suspected MuSK-Ab positive MG and in selecting muscles for molecular, morphologic, or microphysiologic studies in this condition.

Abnormal neuromuscular transmission in cluster headache.

To identify and investigate any dysfunction of neuromuscular transmission in episodic cluster headache. Abnormal neuromuscular transmission has been shown in migraine with aura and in migraine without aura by using single fiber electromyography. Especially for migraine with aura, a genetic cause has been postulated. Episodic cluster headache is a primary headache disorder in which genetic factors may, at times, play a strong role. Single fiber electromyography during voluntary contraction of the extensor digitorum communis muscle, nerve conduction studies of upper and lower extremities, and concentric needle electromyography of the extensor digitorum communis were performed on 6 patients with episodic cluster headache and 6 age-matched normal controls. Twenty potential pairs were recorded from each subject. Twenty individual jitter values and a mean jitter value were calculated for each subject. Both mean individual jitter values and numbers of abnormal individual jitter values were compared in patients with cluster headache versus normal controls. Three of 6 patients with episodic cluster headache showed pronounced neuromuscular transmission abnormalities by single fiber electromyography. None of the controls had any neuromuscular transmission abnormality. Another patient with episodic cluster headache had borderline dysfunction of neuromuscular transmission. Transmission was clearly normal in only 2 of 6 patients with cluster headache. These results suggest that episodic cluster headache may share the same abnormality of neuromuscular transmission observed in migraine.

Literature review of the usefulness of repetitive nerve stimulation and single fiber EMG in the electrodiagnostic evaluation of patients with suspected myasthenia gravis or Lambert‐Eaton myasthenic syndrome

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.

Stimulated single fiber EMG of the frontalis muscle in the diagnosis of ocular myasthenia.

We performed single fiber electromyography by axonal stimulation (SFEMG-AS) of the frontalis muscle of 16 patients with ocular myasthenia gravis (OM) and 33 controls. In the controls, values of mean consecutive differences (MCD) ranged from 5 to 55 micros (average, 14.7 +/- 2.8 micros) and mean MCD of individual MPs was 14. 6 +/- 6.8 micros. All the OM patients showed abnormal SFEMG-AS jitter before prostigmine was administered (mean MCD: 49.19 +/- 21. 82 micros, percentage of blocks: 20.97 +/- 18.53). Twenty or 30 min after prostigmine had been administered, we saw a significant improvement in jitter: mean MCD was 36.38 +/- 22.49 micros (P = 0. 005), and percentage of blocks was 10.16 +/- 18.87 (P = 0.008). The method was well tolerated. We conclude that SFEMG-AS of the frontalis muscle is a sensitive technique for the diagnosis of OM and is easy to carry out.

Concentric needle electrode for neuromuscular jitter analysis.

We used a concentric needle electrode (CNE) with 2 kHZ low-cut filter and a single fiber electrode (SFE) in the same subjects for neuromuscular jitter measurement in the extensor digitorum communis (EDC) and orbicularis oculi (OOc) muscles. At the same session, 20 jitter values were obtained from each subject with each electrode. For EDC (during voluntary contraction), mean jitter values with SFE and CNE were 23.4 +/- 8 micros and 23.3 +/- 8 micros in 10 normals; and 56.8 +/- 28 micros and 57.4 +/- 33 micros in 10 myasthenics. For OOc (during electrical stimulation), mean jitter values with SFE and CNE were 17.9 +/- 5 micros and 16.3 +/- 4 micros in 11 normal subjects, and 41.2 +/- 29 micros and 36.7 +/- 27 micros in 10 myasthenics. For both muscles, the numbers of individual abnormal jitter values with SFE and CNE were highly comparable. Both needles labeled the same patients as having "normal" or "abnormal" neuromuscular transmission. CNE may be an alternative to SFE in neuromuscular jitter analysis.

Single fiber electromyography of extraocular muscles: a sensitive method for the diagnosis of ocular myasthenia gravis.

We performed single fiber electromyography (SFEMG) in the superior rectus and levator palpebralis (SR-LP) muscles of 17 patients with pure ocular myasthenia gravis (MG) and 9 controls. Thirteen patients were also assessed with SFEMG in the orbicularis oculi (OO) muscle. All the MG patients but none of the control subjects showed abnormal SFEMG jitter in the SR-LP muscles. On the other hand, only 62% of the MG patients had abnormal SFEMG jitter in the OO muscle. The procedure was well tolerated by the patients, and complications were minor. We conclude that SFEMG of the SR-LP muscles is a safe and highly sensitive technique for the diagnosis of ocular MG.

Involvement of the external anal sphincter in amyotrophick lateral sclerosis

In amyotrophic lateral sclerosis the striated pelvic floor sphincter muscles are functionally uninvolved, and pathological studies have confirmed the relative resistance of the Onuf nucleus motor neurons. We have evaluated the external anal sphincter (EAS) muscle in 16 patients with ALS using single fiber EMG, and compared the results with the findings in the semimembranosus-semitendinosus (SM-ST) muscles that have innervation from the L-5, S-1, and S-2 segments. The results were compared with a group of controls matched for age and sex. None of the patients or controls had symptomatic sphincter involvement and none of the 4 women studied were parous. Eight patients with ALS showed an increased fiber density in the EAS; 6 had an abnormal neuromuscular jitter. In 1 there was fibrillation in the EAS. In the SM-ST muscle 11 patients showed an increased fiber density, and 7 had an abnormal neuromuscular jitter. In 3 patients with ALS in whom there were abnormal findings in the EAS the bulbocavernosus reflex and pudendal nerve evoked potentials were normal. Neurogenic change was more marked in the SM-ST than in the EAS muscle. These findings show that the EAS is not normal in ALS. However, the relative resistance of the EAS to ALS is sufficient to prevent incontinence, even in the longer-surviving older patients.

Arthrogryposis multiplex congenita due to congenital myasthenic syndrome

Two children, now 5 1 2 and 6 years of age, presented as neonates with hypotonia, multiple joint contractures, ptosis, extraocular weakness, bulbar symptoms, and respiratory distress. Fluctuations and episodic exacerbations of weakness necessitated respiratory support. Both children are developmentally delayed and cannot walk independently, although one child underwent bilateral tenotomies. Biochemical investigations and electromyography, including slow-rate, repetitive nerve stimulation, were normal. Acetylcholine receptor antibodies in serum were absent. Single-fiber electromyography with axonal stimulation revealed prolonged mean jitter in the tibialis anterior and extensor digitorum muscles, with more than 2 abnormal individual jitter values in each muscle. Muscle biopsy demonstrated normal pattern and morphology of muscle fibers; immunohistochemical staining for cholinesterase was positive. Electron microscopy revealed abnormalities in motor endplates: atrophy, flattening of primary synaptic clefts, and paucity of side branches. These findings represent one of the postsynaptic abnormalities (i.e., acetylcholine receptor deficiency or paucity of synaptic folds). Both children improved clinically on pyridostigmine therapy. Arthrogryposis congenital multiplex due to congenital myasthenic syndrome, as diagnosed in our patients, has been reported once before. The diagnosis can be established by clinical history, neurologic examination, and electrophysiologic and pathologic findings. Clinical improvement can be achieved with high-dose anticholinesterase therapy.

Single fibre EMG studies in chronic fatigue syndrome: a reappraisal.

Single fibre EMG studies were carried out on the right extensor digitorum communis muscle in 30 subjects with chronic fatigue syndrome and in 30 age and sex matched controls. Abnormal jitter was seen in five patients with chronic fatigue syndrome. Slight but significant differences between the mean consecutive differences in the remainder of the chronic fatigue subjects and the control subjects were recorded. Overall the differences were so minor that it seems unlikely that a disturbance of neuromuscular function as reflected by jitter measurement has a pathogenetic role. It is suggested that the increased jitter seen may be explained by the effects of the variability of motor unit firing rates on the myogenic component of the jitter.

Remission of myasthenia gravis: clinical, electrophysiological and immunological studies.

The prognosis of 142 patients with myasthenia gravis (MG) was clinically investigated. Forty-nine (35%) had clinical remission (CR) and 23 (16%) good improvement (GI), while 70 (49%) remained in poor condition. Favorable clinical factors for CR were the onset of MG before the age of 20 years, a pre-thymectomy period of less than one year, and a post-thymectomy period of six years or more. Single-fiber electromyography (SFEMG) showed abnormal jitter in nine (47%) of the 19 CR patients, while abnormal jitter was shown in 13 (81%) of the 16 GI patients. Abnormal jitter in CR patients was correlated with the following clinical factors: complication with the thymoma, a period of three or more years from thymectomy to remission, and a remission period of less than six years. An anti-acetylcholine receptor (anti-AChR) antibody was positive in 12 CR patients (63%) as well as in 13 GI patients (81%). Based upon these facts, we point out that true remission seldom occurs in MG patients, and that there exist clinical features that may favorably induce clinical remission. We would like to postulate that electrophysiological and immunological follow-up is indispensable even in CR patients to predict recurrence.

Single fiber EMG in a congenital myasthenic syndrome associated with facial malformations

Six patients with a newly described genetic syndrome in Iraqi and Iranian Jews of congenital myasthenia associated with facial malformations were studied with voluntary and stimulation single fiber EMG (SFEMG). Voluntary SFEMG revealed abnormal jitter in all patients in both extensor digitorum communis (EDC) and orbicularis oculi (OOC) muscles, though much smaller in the clinically unaffected EDC. SFEMG study of OOC muscle by axonal stimulation at rates from 1 to 48 Hz showed the most increased jitter at the highest stimulation frequencies in the majority of end-plates, one-third of which showed maximal jitter at intermediate rates. These results may suggest a postsynaptic abnormality as the underlying cause for the neuromuscular transmission defect, and demonstrate the usefulness of SFEMG in the diagnosis of congenital myasthenia.

Single-fiber electromyography of extraocular muscles in myasthenia gravis

The jitter phenomenon of extraocular muscles (EOMs) was investigated in 11 healthy controls and 42 patients with diplopia and/or blepharoptosis using single fiber electromyography (SFEMG). The authors compared the usefulness of SFEMG of EOMs with two other diagnostic techniques (Tensilon test and the titers of anti-acetylcholine receptor antibodies: Anti-AChR ABs) in the differential diagnosis of myasthenia gravis (MG). The Tensilon test was positive in 72.7% of MG patients. Anti-AChR ABs were detected in 100% of generalized MG patients and in 63.6% of ocular MG patients. SFEMG demonstrated an abnormal jitter phenomenon in all MG patients. The authors conclude that SFEMG of EOMs is the most decisive examination in the differential diagnosis of ocular MG, and recommend its use when the etiology of fluctuating diplopia and blepharoptosis cannot otherwise be established.

Electrophysiologic changes in lumbar spinal cord after cervical cord injury.

Spontaneous activity on the EMG examination is traditionally ascribed to disease of the lower motor neuron when present in muscles well below the level of para- or quadriplegia despite the absence of any detectable peripheral nerve injury. It is uncertain whether it reflects transient paralysis of transmission (related to clinical spinal shock) or irreversible postsynaptic damage. We performed serial EMG studies of lower extremities and paraspinal muscles on eight young, previously healthy adults, commencing 2 to 9 weeks after acute cervical cord injury. All had stimulated single-fiber EMG (SFEMG) studies at 6-month intervals to determine whether irreversible postsynaptic damage of the anterior horn cell had occurred. MRI and nerve conduction excluded patients with evidence of distal cord injury or peripheral neuropathy. All patients had spontaneous activity in all muscles tested, persisting after spinal shock had resolved. Jitter was present on SFEMG in three of eight patients 6 months after injury. Four of five patients retested 12 months after injury had abnormal jitter, including three who initially had normal SFEMG studies. We conclude that there is electrophysiologic evidence of trans-synaptic distal cord dysfunction following acute spinal cord injury. SFEMG studies suggest that anterior horn cell dropout occurs during the 1st year after injury.

Electrophysiological spectrum of inclusion body myositis

We present electrodiagnostic data on 30 patients with inclusion body myositis (IBM) in order to better delineate its electrophysiological features. Comprehensive electromyography (EMG) and nerve conduction studies (NCS) were performed in all cases. Twelve patients had single fiber electromyography (SFEMG). EMG showed abundant short-small motor unit potentials (MUP) with fibrillations and positive sharp waves in 56.6% of patients, and a mixed pattern of large and small MUP in 36.7%. In 6.7%, only "neurogenic" features were seen. NCS were slow in 33.3%. SFEMG revealed a mildly abnormal jitter and a slightly increased fiber density. IBM demonstrates a heterogeneous EMG profile. A pattern of large and small MUP is highly suggestive of IBM but is seen in only about one third of cases.

Fasciculations in motor neuron disease: discharge rate reflects extent and recency of collateral sprouting.

Single fibre EMG recordings were made from 152 fasciculating motor units in 17 patients with motor neuron disease. All recordings showed abnormal jitter, many (75%) displayed intermittent blocking, and most had abnormal fibre density (mean 4.3), demonstrating considerable degrees of collateral sprouting supported by the fasciculating motor units, and varying degrees of functional immaturity of the new axonal twigs and the motor end plates. The SFEMG abnormalities reflecting both the degree and the recency of collateral reinnervation correlated with the mean interdischarge interval, suggesting that the properties of the generator site depend on the functional state of the fasciculating motor unit as a whole.

Adult-onset centronuclear myopathy: evidence against a neurogenic pathology

A case of sporadic adult-onset centronuclear myopathy is presented. EMG was myopathic and nerve conduction study entirely normal. Single-fiber electromyography showed a normal percentage of potential pairs with abnormal jitter, slightly increased mean jitter value, no blocking and normal fiber density. Somatosensory and motor evoked potentials were within the normal limits. While it is still a subject of debate whether centronuclear myopathy is neuropathic or myopathic in origin, our findings are against peripheral nerve and CNS involvement.

The single-fiber EMG in chronic demyelinating neuropathy.

Various parameters of single- fiber electromyography (SFEMG) were studied in 19 patients with electrophysiologically and histologically proven chronic demyelinating neuropathy. The mean duration of disease at the time of testing was four years. Motor nerve conduction in the median nerve was abnormal in all patients, whereas sensory nerve conduction was abnormal in all but one. Needle EMG in the extensor digitorum communis (EDC) muscle showed rare fibrillations and fasciculations and some abnormal motor unit potentials in most of patients. SFEMG in the EDC muscle showed an increased fiber density in seven cases (37%) and minimally abnormal jitter in 14 cases (74%). Single-fiber action potentials were stable, whereas blocking was rare. Fiber density was significantly increased in patients with fibrillation in the conventional needle EMG. Our study showed that the SFEMG is mildly abnormal in many patients with demyelinating neuropathy and that this test is useful in detecting and quantitating axonal degeneration in demyelinating neuropathy.

Post-viral fatigue syndrome: evidence for underlying organic disturbance in the muscle fibre.

Ten patients with post-viral fatigue syndrome and abnormal serological, virological, immunological and histological studies were examined by the single-fibre electromyographic (EMG) technique after excluding concurrent problems in the neuromuscular system. No abnormality of fibre density was noted but all patients had abnormal jitter values. Very high jitter values were not associated with impulse or concomitant blocking. The findings confirm the organic nature of the disease. A muscle membrane disorder probably arising from defective myogenic enzymes is the likely mechanism for the fatigue and the single-fibre EMG abnormalities. This muscle membrane defect may be due to the effects of a persistent viral infection.