Added value of electromyography in the diagnosis of myopathy: A consensus exercise.

OBJECTIVE: Currently, neurologists may primarily rely on blood biomarkers, muscle biopsy, MRI, and genetics in the diagnostic work-up of suspected myopathy. Using expert consensus as diagnostic reference standard, this study addressed the added value of electrodiagnostic medicine (EDX) in diagnosis of myopathies. METHODS: One hundred ninety-four EDX evaluations of patients with a peer-review consensus diagnosis of myopathy were collected by seven European centres. Each patient was given three different consensus diagnoses: (1) the EDX diagnosis solely based on EDX results, (2) the pure clinical diagnosis based on all available information except EDX results, and (3) the final diagnosis including EDX and all additional information. The myopathies were grouped as muscular dystrophy (45), inflammatory myopathy (46), other aetiology (36) or unknown aetiology (67). RESULTS: Higher diagnostic probabilities for myopathy were seen in the final diagnosis compared to the pure clinical diagnosis (p<0.001). Adding EDX information increased the diagnostic probability of myopathy in 67 patients (34.4%). The greatest increase was seen for myopathies of unknown aetiology. CONCLUSIONS: EDX has a major impact in the diagnosis of myopathies of unknown aetiology. In genetically or biopsy proven myopathies, EDX generally supports the diagnosis. SIGNIFICANCE: EDX is still a useful tool in the diagnostic work-up of most patients with suspected myopathy.

[Phenotypic heterogeneity and phenotype-genotype correlations in dystrophinopathies: Contribution of genetic and clinical databases]. / Variabilité phénotypique et corrélations génotype-phénotype des dystrophinopathies : contribution des banques de données.

The objective of this work was to study the natural history of dystrophinopathies and the genotype-phenotype correlations made possible by the development of the clinical part of the French DMD database. The collection of 70,000 clinical data for 600 patients with an average longitudinal follow-up of 12years enabled clarification of the natural history of Duchenne and Becker muscular dystrophies and clinical presentations in symptomatic females. We were able to specify the phenotypic heterogeneity of motor, orthopedic and respiratory involvements (severe, standard and intermediary form), of the cardiac disorder (severe, standard or absent cardiomyopathy, absence of correlation between motor and cardiac involvements), and of brain function (mental deficiency in the patients with Becker muscular dystrophy, psychopathological disorders in dystrophinopathies). Phenotypic variability did not correlate with a specific mutational spectrum. We propose a model of phenotypic analysis based on the presence or not of muscular and cardiac involvements (described by age at onset and rate of progression) and brain involvement (described by the type and the severity of the cognitive impairment and of the psychological disorders). The methodology developed for the DMD gene can be generalized and used for other databases dedicated to genetic diseases. Application of this model of phenotypic analysis for each patient and further development of the database should contribute substantially to clinical research providing useful tools for future clinical trials.

Generalised sensory system abnormalities in amyotrophic lateral sclerosis: a European multicentre study.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is defined as a disease of the motor neurones, although several studies indicate involvement of the sensory nervous system. AIM: To evaluate the sensory nerve conduction studies (NCS) in 88 patients with ALS as part of a European multicentre study. METHODS: Seven European clinical neurophysiologists examined consecutive series of ALS patients. The examinations were peer reviewed, and the diagnosis of ALS was confirmed clinically. RESULTS: 20 (22.7%) patients with ALS had sensory NCS abnormalities in at least one nerve. Of those, 11 (12.5% of all patients) obtained an additional peer review diagnosis of electrophysiological polyneuropathy. There was no difference between the subgroups of patients with normal versus abnormal sensory NCS findings with respect to age, duration and region of onset. CONCLUSION: The findings support previous reports of sensory involvement in ALS, and raise the question of whether patients with ALS with sensory nerve abnormalities represent a variant of ALS. ALS associated with generalised sensory system abnormalities may be consistent with degeneration of motor neurones and dorsal root ganglion cells.

Amplitude, area and duration of the compound muscle action potential change in different ways over the length of the ulnar nerve.

OBJECTIVE: To study physiological changes of the compound muscle action potential (CMAP) obtained from stimulation at different sites over the full length of a motor nerve and to study possible effects of anthropometrical factors. METHODS: Multicentre study of ulnar motor nerve conduction in five segments to Erb's point performed bilaterally on 100 healthy subjects aged 17-83 years. RESULTS: CMAP amplitude decreased linearly with conduction distance (0.31%/cm) from wrist to Erb's point. CMAP area decreased with the square of conduction distance. Decrease in area was smaller than decrease in amplitude especially distally. CMAP duration increased linearly (0.17%/cm). Amplitude decay correlated with age, height and BMI and dispersion correlated with age and height. There were no correlations between area decay and anthropometrical factors. There was no significant inter-examiner variation. CONCLUSIONS: Area decay may be preferred to amplitude decay in the evaluation of conduction block over short segments due to smaller physiological changes and independence of anthropometrical factors. The absence of inter-examiner variation indicates that the results are robust and may be used by other laboratories. SIGNIFICANCE: This study provides knowledge of physiological changes of CMAP parameters that may be of importance in the evaluation of nerve pathology, in particular conduction block.

[Assessment of muscle function in pathology with surface electrode EMG]. / Electromyographie de surface et fonction musculaire en pathologie.

Surface electromyography (SEMG) had been and is still widely used in kinesiology and fatigue studies. Its use in routine clinical neurophysiology remains limited. Patients are requiring non-invasive EMG, which could also benefit to physicians and health care system looking for tools to evaluate muscle function in neuromuscular diseases as well as for therapeutic trials. This is the aim of our clinical studies. We apply SEMG envelope signal analysis acquired from maximal voluntary contractions, and the related compound muscle action potential (CMAP). These unspecific parameters cannot be used for neuromuscular diseases diagnosis, objective under study by many research teams. In nerve lesions follow-up studies, our SEMG procedure is related to motor clinical progression. We are currently evaluating it in chronic neuromuscular diseases. The respective contribution in neuromuscular disorders of the different neurophysiology techniques has still to be confirmed, and compared to force measurement by manual or quantitative testing, dynamometry, other suggested techniques (spectroscopy, imaging) as well as functional scales.

[Surface electromyography procedure]. / Stratégie d'utilisation de l'EMG de surface.

Surface electromyography (SEMG) is not yet able to substitute needle EMG for diagnosing neuromuscular diseases in our current clinical neurophysiological practice. Several research groups have been working to reach this goal. Thus, we already have available, though imperfect and open to criticism, tools to apply SEMG to follow-up studies of neuromuscular diseases. There are enough scientific data to integrate validated tools into EMG equipment, to provide recommended electrodes and developed techniques and methods for recording and analysing all SEMG components, so that we could study the suggested standardised parameters in our clinical routine context. Independently of the accuracy of clinical indications for the chosen methods, the requirements of sensitivity, specificity and reproducibility should be as substantial for ENG as for needle or surface EMG. They suppose an equal demanding procedure in doing exams and interpreting results. The respective contribution of ENG and needle or surface EMG is still to be confirmed. Respective value and limitations of the force measurements by manual or quantitative testing, functional scales, SEMG or motor unit number counting are not yet evaluated in follow-up studies of neuromuscular diseases.

Variation in the classification of polyneuropathies among European physicians.

OBJECTIVE: Considerable debate still exists regarding the classification of polyneuropathies (PNPs) into predominantly demyelinating, predominantly axonal loss, mixed or unclassified. This study was designed to determine the variation among physicians in the classification of PNPs by using the European Standardized Telematic tool to Evaluate Electromyography knowledge-based systems and Methods (ESTEEM) multicenter database. METHODS: Seven physicians from 6 laboratories in Europe sent a total of 156 prospectively collected cases of PNP with electromyography (EMG) data including diagnosis (examination diagnosis) to the database. Each physician interpreted the electrophysiological data from all cases (interpretation diagnosis) and a final diagnosis was given at the consensus meetings of the group (consensus diagnosis). RESULTS: Comparison of each physician's examination diagnosis with his/her interpretation diagnosis, i.e. intra-physician variation, showed a change towards less classified PNPs (P < 0.05). Interpretation diagnoses showed large inter-physician variation in the classification of PNPs. The consensus group was more cautious than individual physicians in classifying PNPs as mixed and axonal. The probability of the consensus diagnosis increased with increasing number of abnormal motor and sensory segments tested. CONCLUSIONS: Recognition of variation in classification of PNP as shown in this study and suggesting standards of good clinical practice developed by a consensus group may increase the quality of EMG practice.

Charcot-Marie-Tooth disease and sleep apnoea syndrome: a family study.

BACKGROUND: Charcot-Marie-Tooth (CMT) disease is a genetically heterogeneous group of hereditary motor and sensory polyneuropathies in which sleep apnoea has rarely been reported and no causal relation shown. We looked for an association between the most common subtype of CMT disease (CMT1A) and sleep apnoea syndrome. METHODS: Having diagnosed sleep apnoea and CMT in one family member (index case), we prospectively investigated 13 further members not previously suspected of having neuropathy or apnoeas. All had a neurological examination, electroneuromyography, polysomnography, and genetic testing for CMT disease. FINDINGS: 11 of the 14 family members had the autosomal dominant demyelinating form of CMT disease with PMP22 gene duplication on chromosome 17. Whatever their neurological disability, all 11 individuals had sleep apnoea syndrome with a mean (SD) apnoea-hypopnoea index of 46.6/h (28.5) of sleep (normal value <15/h). The remaining three family members were free from neuropathy and sleep apnoea syndrome. Sleep apnoea and neuropathy severity were highly correlated; the compound muscle action potential (CMAP) amplitude of the median nerve was inversely correlated with the apnoea-hypopnoea index (r=-0.69, p=0.029). The severity of neuropathy and sleep apnoea were higher in male CMT individuals and were correlated with age and body mass index. No wake or sleep diaphragmatic dysfunction was shown. INTERPRETATION: We think that sleep apnoea syndrome is related to a pharyngeal neuropathy. Upper airway dysfunction, previously described in the CMT2C subtype, might be a clinical expression of the CMT1A subtype, to which familial susceptibility could predispose.

Exercise test in muscle channelopathies and other muscle disorders.

We studied the percentage change in compound muscle action potential (CMAP) amplitude and area during and after a 5-min maximal contraction of the muscle. The exercise test (ET) was performed on 64 patients with different muscle disorders and on 46 normal controls. The range of normal ET values was defined as the mean + 2 SD of the control values. The mean sensitivity of the test was 63% in the whole group with ion channel muscle disorders, the highest sensitivity being seen in primary periodic paralysis (81%) and the lowest in chloride channelopathies (17%). In thyrotoxic periodic paralysis, the ET was abnormal in the three of the four patients studied. In patients with myotonic dystrophy, a smaller than normal increase in CMAP amplitude occurred during and after exercise, whereas in proximal myotonic myopathy a normal initial increase in CMAP amplitude was followed by an abnormal decrement. We conclude that the ET can be of use in confirming abnormal muscle membrane excitability in patients with calcium and sodium channelopathies and thyrotoxic periodic paralysis. In chloride channelopathy, the test may also be abnormal, but shows no, or only a small, increase in amplitude or area in the immediate postexercise period. The test may also be abnormal in proximal myotonic myopathy, but is normal in myotonic dystrophy.