A comparison of concentric needle electromyography, quantitative EMG and single fibre EMG in the diagnosis of neuromuscular diseases

Can Wavelet Denoising Improve Motor Unit Potential Template Estimation?

Background:

Electromyographic (EMG) signals obtained from a contracted muscle contain valuable information on its activity and health status. Much of this information lies in motor unit potentials (MUPs) of its motor units (MUs), collected during the muscle contraction. Hence, accurate estimation of a MUP template for each MU is crucial.

Objective:

To investigate the possibility of improving MUP template estimation using the wavelet denoising technique.

Material and Methods:

In this analytical study, several MUP template estimators were developed by combining conventional estimation methods and wavelet denoising techniques. A MUP template was initially estimated using conventional methods such as mean, median, median-trimmed mean, or mode. Thereafter, it was post-processed using the wavelet denoising technique.

Results:

Evaluation results of the studied estimators using 40 simulated EMG signals with a true template for each constituent MUP train showed that augmented wavelet- based template estimation methods are more reliable than conventional methods. However, on average, wavelet denoising was not much effective. Around 40 MUPs of a MU is sufficient to estimate its MUP template.

Conclusions:

Although wavelet techniques are effective in EMG signal analysis, here wavelet denoising did not practically improve MUP template estimation. Considering computational simplicity and estimation error, the two methods median and median-trimmed mean are practical estimators that can provide a good estimation of a MUP template for a MU when approximately 40 MUPs are available. Nevertheless, the baseline noise level in the MUP templates estimated using the median-trimmed mean method is slightly lower than that in the templates estimated using the median method.

Changes in intracellular action potential profile affect parameters used in turns/amplitude analysis

The influence of changes in the intracellular action potential (IAP) spatial profile on motor unit potentials (MUPs), number of turns per second (NTs), and mean turn amplitude were simulated and analyzed. We show why measurement of NTs was "the best indicator of neurogenic affection" and why the lower diagnostic yield of turns/amplitude analysis in myopathy could be due to changes in IAP shape caused by elevated free calcium concentration. The results explain the complications observed when interference electromyographic signals obtained during high levels of isometric contractions were analyzed. We show that, in contrast to earlier assumptions, the effect of increased IAP spike duration on NTs was stronger than that of a decrease in muscle fiber propagation velocity (MFPV). The decrease in the NTs could occur without a drop-out of MUs and/or a decrease in their firing rates, and without a change in MFPV and synchronous firing.

The role of different EMG methods in evaluating myopathy

For the diagnosis of myopathy, EMG may have an important role along with blood tests, muscle biopsies and genetic testing. This review evaluates different EMG methods in the diagnosis of myopathy. These include manual analysis of individual motor unit potentials and multi-motor unit potential analysis sampled at weak effort. At high effort, turns-amplitude analyses such as the cloud analysis and the peak ratio analysis have a high diagnostic yield. The EMG can seldom be used to differentiate between different types of myopathy. In the channelopathies, myotonia, exercise test and cooling of the muscle are helpful. Macro-EMG, single-fibre EMG and muscle fibre conduction velocity analysis have a limited role in myopathy, but provide information about the changes seen. Analysis of the firing rate of motor units, power spectrum analysis, as well as multichannel surface EMG may have diagnostic potential in the future. EMG is of great importance in the diagnosing of patients with myopathy, preferably a needle electrode and quantitative analyses should be used. A combination of a method at weak effort as well as a method at stronger effort seems optimal.

[Current trends in the development of clinical electromyography]

<zakljucak> Kombinovana primena EMG tehnika uz pomoc kompjutera i standardizovanih softvera omogucava novi pristup u sagledavanju mikrofiziologije i mikropatologije MJ: od nivoa pojedinacnih misicnih vlakana (mikro EMG), preko njihove funkcije i anatomske strukture unutar jedne MJ (standardni EMG i skenirajuci EMG) do elektrofizioloskih karakteristika celokupne teritorije MJ u ispitivanom misicu (makro EMG) (slika 13). Navedene elektrofizioloske tehnike mogu da opisu fizioloski status MJ i pojedinacnih misicnih vlakana u vise detalja nego sto je to bilo moguce ranije koriscenjem samo standardne EMG. Ove tehnike pruzaju dragocenu pomoc ne samo u dijagnostici vec i u razumevanju patofizioloskih procesa koji se desavaju u NB.

Seronegative generalised myasthenia gravis: clinical features, antibodies, and their targets

Myasthenia gravis (MG) is a well-recognised disorder of neuromuscular transmission that can be diagnosed by the presence of antibodies to the acetylcholine receptor (AChR). However, some patients (about 15%) with generalised MG do not have detectable AChR antibodies. There is some evidence, however, that this "seronegative" MG is an antibody-mediated disorder. Plasma from patients with the disorder seems to contain various distinct humoral factors: IgG antibodies that reversibly inhibit AChR function; a non-IgG (possibly IgM) factor that indirectly inhibits AChR function; and an IgG antibody against the muscle-specific kinase (MuSK). The presence of antibodies against MuSK appears to define a subgroup of patients with seronegative MG who have predominantly localised, in many cases bulbar, muscle weaknesses (face, tongue, pharynx, etc) and reduced response to conventional immunosuppressive treatments. Moreover, muscle wasting may be present, which prevents complete response to these therapies.

Comparison of quantitative techniques in anal sphincter electromyography

Data comparing results and utility of different quantitative electromyographic (EMG) techniques are limited. In the present study, we analyzed the EMG signal from the external anal sphincter (EAS) muscle using three techniques of motor unit potential (MUP) analysis, and a technique of interference pattern (IP) analysis. We examined 56 patients with damage to the cauda equina or conus medullaris, and 64 control subjects. Using manual-MUP and multi-MUP analysis about 20 MUPs, using a single-MUP technique about 10 MUPs, and using turn/amplitude (T/A) analysis about 20 IP samples were obtained. The sensitivities of these techniques in distinguishing neuropathic from control muscles were calculated. The single-MUP technique detected 63%, manual-MUP 57%, and multi-MUP analysis 62% of neuropathic muscles, and MUP parameters obtained by each of these differed significantly from the other. The sensitivity of T/A analysis of IP was 29%. Our results confirm the need for separate MUP normative data for each of the MUP analysis techniques, and favor them over the IP analysis technique. The normative data presented for the EAS muscle should improve and promote quantitative EMG in patients.

EMG-interference pattern analysis

The EMG interference pattern, built up of single motor unit action potentials, may be analyzed subjectively, or objectively by computer aided, quantitative methods, like counting of zero-crossings, counting of spikes, amplitude measurements, integration of the area under the curve, decomposition techniques, power spectrum analysis and turn/amplitude analysis. Since the shape of the interference pattern of healthy muscles is dependent on age, sex, force, muscle, temperature, fatigue, fitness level, recording site and surrounding tissue, electrode type, sensitivity, filters, sampling frequency and threshold level, all methods of analyzing the IP have to be standardized. Quantitative methods of analyzing the EMG interference pattern may be used for monitoring botulinum toxin therapy of dystonia and spasticity, quantifying spontaneous activity, assessment of chronic muscle pain, neuro-urological and proctological function, and diagnosing neuromuscular disorders. For diagnostic purposes, the methods favored are those that use needle electrodes and do not require measurement or monitoring of muscle force. The most well-evaluated methods are those using turn/amplitude analysis, like the cloud methods and the peak-ratio analysis. Peak-ratio analysis has the advantage that reference limits are easy to obtain and that its utility is well established and confirmed by several investigations. Overall, automatic methods of EMG interference pattern analysis are powerful tools for diagnostic and non-diagnostic purposes.

The utility of interference pattern analysis

The interference pattern of the electrical activity of muscle can be quantified by amplitude measurements, different spike counting methods, and power spectrum analyses. Interference pattern analysis (IPA) methods are used to describe the degree of activation of different muscles, muscle fatigue, occupational work, muscles in chronic pain syndromes, disused muscle, and dystonic muscle treated with botulinum toxin. In patients with neuromuscular disorders, the turns/amplitude analysis is useful for diagnosis. High diagnostic yields can be obtained without force measurements, for example, by using the amplitude as an indicator of force (the peak ratio method) or plotting the amplitude against the turns (cloud analysis). The diagnostic possibilities of the power spectrum analysis and the motor unit firing rate obtained by decomposition techniques are still unclear.

AAEE minimonograph #29: automatic quantitative electromyography

The present status of different computerized methods of automatic quantitative electromyography are reviewed. Interference pattern methods-turns analysis, spectral analysis-are efficient, but the results usually cannot be directly related to the physiological properties of the motor units. Integration analysis does not currently have a major role in diagnostic electromyography. Traditional measurement of single motor unit action potentials during weak contraction can be facilitated and made more objective with computer assistance, but only the lowest-threshold motor units in the muscle are amenable to study. A new class of methodologies under development permit the decomposition of interference patterns into their constituent motor unit action potentials for measurement of configurational and behavioral properties. Patient data from these various methods can be statistically compared with normative data bases available on-line in computerized electromyographs. Both quantitative and quantitative electromyography have applications in the neuromuscular electrodiagnostic examination.