Automatic analysis of the electromyographic interference pattern. Part I: Development of quantitative features

We have developed three new features of the electromyographic interference pattern (IP), based on the turns and amplitude of the signal, to quantitate some of the features of the IP that are usually assessed subjectively by an electromyographer. The activity measures the fullness of the IP. The upper centile amplitude (UCA) defines the upper limit of the maximum peak-to-peak amplitude of the motor unit action potentials (MUAPs) contained in the IP. The number of small segments (NSS) measures the complexity of the IP, which is a reflection of the polyphasicity of the component MUAPs. The activity and the logarithm of the UCA correlate strongly with the force of muscle contraction at which the IP is measured. The NSS initially increases with the force of contraction and becomes relatively constant at higher force levels. The normal values of these features and the interpretation of their relationships are described in companion papers.     

Turns-amplitude analysis of the electromyographic recruitment pattern disregarding force measurement. II. Findings in patients with neuromuscular disorders.

Turns-amplitude analysis of the electromyographic recruitment pattern was performed on-line in the brachial biceps muscle of 46 patients with neuromuscular disorders using the mean amplitude as an indicator of force. The parameters, peak-ratio (PR) and number of time intervals (TI) from 0 to 1.5 ms, were increased in patients with myopathy. In patients with neurogenic involvement, the characteristic pattern was a decreased PR and a decreased incidence of TI between 0 and 1.5 ms. The results indicate that the two parameters supplement each other as some of the patients were identified only by one or the other. In patients with myopathy, the method had a higher diagnostic yield than the individual motor unit action potential analysis. The method is objective, fast, and reliable.     

Automatic analysis of the electromyographic interference pattern using the turns: amplitude ratio

This study was performed to compare different techniques of analyzing the electromyographic interference pattern (IP). Recordings were made from the biceps muscle with a concentric needle electrode at different sites and at different constant levels of voluntary contraction. The number of turns per second (NT), the mean amplitude change between successive turns (MA) and NT:MA ratio were determined for epochs of 1 sec duration. Normal limits of individual epoch NT:MA ratios and the mean value of NT:MA ratio obtained from all epochs in each muscle were determined. The mean NT:MA ratio was less in normal males than in females. IP recordings were made in the biceps muscle of 69 patients with neuropathy and 54 patients with myopathy, though this muscle was not necessarily affected by the disease in all patients. The IP was abnormal by visual inspection in 82% of patients compared to 61% based on NT:MA ratio and 74% using a technique that automatically quantitates some features of the IP that are assessed subjectively by an electromyographer. All techniques demonstrated IP abnormalities in more than 80% of the muscles that were moderately to severely weak. Though measuring the NT:MA ratio without monitoring the force of contraction is not as sensitive as other IP analysis techniques, it may be useful in quantitating abnormalities when other techniques are not available.     

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part I: Turns and amplitude measurements

The electromyographic (EMG) interference pattern (IP) was simulated by adding together motor unit action potentials (MUAPs) of different sizes that had been recorded by a concentric needle EMG electrode. The number of turns (NT) of the simulated IP increased with the number of MUAP discharges. The mean amplitude (MA) difference between successive turns in the IP increased when large amplitude MUAPs were added. Our analysis demonstrates that the MA of the IP is determined mainly by the amplitude of large MUAPs in the signal and that large amplitude spikes are more likely to be generated by single large amplitude MUAPs than by summation of several small amplitude MUAPs.     

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part II: Activity, upper centile amplitude, and number of small segments

We have defined three new features of the electromyographic (EMG) interference pattern (IP): activity, upper centile amplitude (UCA), and number of small segments (NSS). These parameters were measured in simulated IPs constructed by adding together motor unit action potentials (MUAPs) recorded with a concentric needle EMG electrode. The activity increases linearly with the number of MUAP discharges to approximately 80% of its theoretical maximum value. The UCA correlates strongly with the peak-to-peak amplitude of the largest MUAP in the IP and the mean segment amplitude and does not depend on the discharge rate of the largest MUAPs. We infer that the UCA defines the upper limit of the peak-to-peak amplitude of the MUAPs contained in the IP. The NSS increases with the number of MUAP discharges, but reaches a constant value at higher MUAP discharge rates, probably because small amplitude MUAPs are masked by the large amplitude MUAPs. The potential value of these parameters in automated IP analysis is discussed.     

Peak-ratio interference pattern analysis in the detection of neuromuscular disorders

Peak-ratio interference pattern analysis (peak-ratio method) is said to have a high sensitivity and to be independent of sex and age. This study was carried out to prove or disprove these findings. The peak-ratio method and qualitative motor unit action potential (MUAP) analysis were applied to the right brachial biceps and anterior tibial muscles of 44 healthy subjects, aged 23–87 years, 25 neuropathy patients, aged 21–83 years, and 29 myopathy patients, aged 19–70 years. Peak-ratio parameters were independent of sex and age. They tended to be lower in the anterior tibial muscle than in the brachial biceps muscle. Neuropathy patients typically showed decreased peak-ratio, short time intervals and increased amplitude/turn. Myopathy patients typically showed increased peak-ratio, turns/s and short time intervals. The sensitivity of the peak-ratio method was 72% for neuropathy patients and 59% for myopathy patients. The sensitivity of the peak-ratio method was similar to that of the MUAP analysis in neuropathy patients and higher than that of the MUAP analysis in myopathy patients. The specificity of the peak-ratio method was 80%. The peak-ratio method proved to be a valuable, supplementary electromyographic tool for the detection of neuromuscular disorders.     

Turns-amplitude analysis of the electromyographic recruitment pattern disregarding force measurement. I. Method and reference values in healthy subjects.

We used turns-amplitude analysis to characterize the EMG recruitment pattern disregarding force measurement. The electrical muscle pattern of the brachial biceps (BB), abductor pollicis brevis (APB), medial vastus (MV), and anterior tibial (AT) muscles was analyzed during progressive increase in force from rest to maximum using the mean amplitude as an indicator of the force of the muscle. The following parameters were obtained on-line: the maximal ratio of turns to mean amplitude (peak-ratio, PR), the mean amplitude, and the number of time intervals (TI) between turns at PR and at near maximum force (NMF). The highest PR values were obtained in BB, the lowest in MV. Analysis of the distribution of the TI between turns at different degrees of voluntary contraction showed fewer spikes with short duration and small amplitude at high force compared with low force.     

Automatic analysis of heart rate variation: II. Findings in patients attending an EMG laboratory

An automatic method was used to measure the heart rate variation with breathing in patients with different neuromuscular conditions attending a laboratory of electromyography (EMG). The objective was to determine the frequency of abnormalities in various conditions and the relationship between R-R variation and different nerve conduction parameters. The percentages of reduced R-R variation were 73% in diabetics, 35% in Guillain-Barré syndrome, 22% in amyotrophic lateral sclerosis, and 50% in amyloidosis. R-R variation in diabetics was significantly correlated to most parameters of nerve conduction. In Guillain-Barré syndrome it correlated significantly with the ulnar and median M-response amplitudes. Most patients with myopathies showed normal R-R variation.     

Molecular diagnosis of inheritable neuromuscular disorders. Part II: Application of genetic testing in neuromuscular disease

Molecular genetic advances have led to refinements in the classification of inherited neuromuscular disease, and to methods of molecular testing useful for diagnosis and management of selected patients. Testing should be performed as targeted studies, sometimes sequentially, but not as wasteful panels of multiple genetic tests performed simultaneously. Accurate diagnosis through molecular testing is available for the vast majority of patients with inherited neuropathies, resulting from mutations in three genes (PMP22, MPZ, and GJB1); the most common types of muscular dystrophies (Duchenne and Becker, facioscapulohumeral, and myotonic dystrophies); the inherited motor neuron disorders (spinal muscular atrophy, Kennedy's disease, and SOD1 related amyotrophic lateral sclerosis); and many other neuromuscular disorders. The role of potential multiple genetic influences on the development of acquired neuromuscular diseases is an increasingly active area of research.     

Immunosuppressive and immunomodulatory therapies for neuromuscular diseases. Part I: Traditional agents

Immunosuppressive and immunomodulatory therapies have had a major effect on the treatment of immune-mediated neuromuscular diseases. After the landmark introduction of synthetic corticosteroids, other therapies have become available, including plasma exchange (PLEX), immunoglobulin G (IgG), and steroid-sparing immunosuppressive drugs. More recently, novel biologically derived and antigen-specific pharmaceuticals have entered neuromuscular practice. Various levels of evidence guide the use of these treatments. This article reviews current immune-based therapies in neuromuscular diseases and is divided into two parts. Part I provides an update on the evidence and use of traditional therapies, such as corticosteroids, PLEX, intravenously delivered IgG (IVIG), and steroid-sparing immunosuppressive drugs. Part II focuses on the recently US Food and Drug Administration–approved therapies eculizumab and subcutaneous IgG (SCIG), the current indications for rituximab in neuromuscular disease, and on novel immunosuppressive therapeutic approaches under development.     

Recurrence quantification analysis of surface electromyographic signal: sensitivity to potentiation and neuromuscular fatigue

This study aimed to assess the capacity of recurrence quantification analysis (RQA) to detect potentiation and to determine the fatigue components to which RQA is sensitive. Fifteen men were divided in two groups [8 endurance-trained athletes (END) and 7 power-trained athletes (POW)]. They performed a 10-min intermittent (5s contraction, 5s rest) knee extension exercise at 50% of their maximal voluntary isometric contraction. Muscular fatigue and potentiation were evaluated with neurostimulation technique. Mechanical (peak torque, Pt) and electrophysiological (M-wave) responses following electrical stimulation of the femoral nerve were measured at rest and every 10s throughout exercise. Vastus lateralis muscle activity (root mean square, RMS) was recorded during each contraction, and RMS was normalized to M-wave area (RMS/M). During contraction, muscle activity was analyzed with RQA to obtain the percentage of determinism (%Det). At the beginning of exercise, a significant Pt increase (+52%, P<0.001) was observed in both groups, indicating potentiation. At this time, %Det remained constant in both groups, indicating that RQA did not detect potentiation. Thereafter, Pt decreased in POW from 5min 30s of exercise (-30%, P<0.001), reflecting impairment in excitation-contraction coupling, and %Det increased from 3min 30s (P<0.01). In END, Pt remained high and %Det was unchanged. These two results indicated that RQA detected the peripheral component of fatigue. Conversely, RQA did not detect central adaptation to fatigue since %Det remained constant when a significant increase in RMS/M (P<0.01) appeared in END.     

Notes on the history of the prion diseases. Part II

The protein-only theory of transmission of the prion diseases remains controversial. Other mechanisms such as the virus, virino, and viroid hypotheses are still under consideration. All these fit in the concept of 'slow' infections that had been proposed in 1954 by Bjorn Sigurdsson, an Icelandic pathologist. Regardless of the exact mode of infection, the presence of prions in the brain has served to unite Creutzfeldt-Jakob disease (CJD), the Gerstmann-Str?ussler-Scheinker syndrome and fatal familial insomnia, as well as scrapie and a number of other animal diseases, into a single pathological entity, the transmissible spongiform encephalopathies. The appearance of bovine spongiform encephalopathy in the United Kingdom and its putative relationship to new variant CJD, have put a new and unpredictable light on these unusual and uncommon diseases.     

Autoimmune diseases in the pedigrees of schizophrenic and control subjects

Autoimmune diseases aggregate in individuals and within pedigrees, and it has been postulated that autoimmune mechanisms may account for a proportion of schizophrenia. Structured questionnaires were used to interview the mothers of 121 DSM-III-R schizophrenic patients and the mothers of 116 controls in order to determine the prevalence of schizophrenia and of autoimmune diseases in their pedigrees. Patients with a schizophrenic first degree relative were significantly more likely to also have a parent or sibling with an autoimmune disease (60% vs. 20%, OR=6.1, 95% CI=2.3−16.5, p=0.0003). A significant excess of insulin dependent diabetes mellitus (IDDM) was present in the parents and siblings of schizophrenic patients (OR=9.65, 95% CI=1.3−429.2, p=0.009). These findings suggest that autoimmune mechanisms may play a role in the aetiology of schizophrenia, particularly familial schizophrenia. Associations have been established between autoimmune diseases and the HLA encoding genes of the major histocompatibility complex on chromosome six, and it may be that some of the genetic liability to schizophrenia involves these genes.     

Family model and mental anorexia. Part II. Intergenerational pattern of relationships

Concepts analysing intergenerational transmission in families of anorectic patients are presented. The researches indicate that the problems associated with the autonomy process in patients with anorexia nervosa may be rooted in experiences of former generations and connected with specific patterns of family relationships. From among these, mourning and suffering bonds, sense of justice, value of sacrifice philosophy and particular delegations addressed to daughters seem essential. Such a selection emphasises co-evolutional character of separation-individuation process and justifies the place of family therapy in therapeutic process.     

Expression of class I and class II MHC antigens in neuromuscular diseases

The distribution of HLA class I and class II antigens has been investigated in cryostat sections of a series of 200 skeletal muscle biopsy specimens from patients with various neuromuscular disorders. Normal muscle fibres expressed no detectable class I antigens, whereas muscle fibres of patients with inflammatory myopathies and Duchenne (DMD) and Becker (BMD) muscular dystrophy showed consistently strong expression. In other neuromuscular diseases expression of class I antigens was more variable. No expression of class I antigens was observed on muscle fibres in samples from fetuses "at risk" for DMD and BMD or from female carriers of these disorders. The immunocytochemical assessment of HLA class I antigen expression was confirmed by a quantitative radioimmunoassay which demonstrated a 3-fold increase in the level of expression in muscle samples from patients with DMD and juvenile dermatomyositis. Class II antigen expression was never observed on muscle fibres in biopsies from normal individuals or any of the neuromuscular disorders. However, these antigens were expressed by endothelial cells present in these samples. Muscle specimens from fetuses and early in postnatal life showed very limited expression of class II antigens. They were expressed at a reduced level by about 3 months of age, but strong expression of class II antigens was not observed until about 1 year of age. The mechanism of induction of class I antigen expression in diseased muscle is not known. The appearance of class I antigens on diseased muscle may make the affected tissue a target for cytotoxic T cells and may thus have a role in muscle fibre damage in inflammatory myopathies and the X-linked muscular dystrophies.