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

Quantitative Evaluation of Interference Patterns on Electromyography in Neuropathy

OBJECTIVE

The aim of this study was to develop a quantitative evaluation method of interference patterns on needle electromyography that is easy to apply in clinical use and to examine its usefulness. Diagnostic electrophysiological assessments are important for physiatrists, and correct diagnosis and assessment are essential for proper rehabilitation.

DESIGN

A total of 112 maximum interference patterns of upper extremity muscles suspected of being affected by neuropathy were quantitatively evaluated based on the parameters of integration values, mean amplitudes, the number of peaks, and activity. "Activity" was defined as the sum of the time during which myoelectric signals were recorded during 1 sec with maximum voluntary contraction, and it was expressed as a percentage. The relationships of the previous parameters with spontaneous pathological potentials and polyphasic motor unit potentials were examined.

RESULTS

The area under the curve of the receiver operating characteristic curve for the diagnosis of neuropathy was the highest using activity (0.917). The integral value and mean amplitude were useful for the diagnosis of cases with chronic neuropathy showing slightly decreased interference patterns.

CONCLUSIONS

The quantitative evaluation of the maximal contraction interference pattern in this study was useful for the diagnosis of neuropathy.

A strong linear relationship between Turns/Amplitude peak ratio and ratio at maximal effort

In EMG interference pattern analysis, the peak value of turns to mean amplitude ratio [peak(T/A)] is an established clinically significant marker, but its calculation requires specific software available only in few EMG apparatuses. On the contrary, the turns to mean amplitude ratio obtained at maximal muscle contraction (T/Amax) is easily calculated but less well standardized. We aimed to quantitatively assess the association between T/Amax and peak(T/A). Data were derived from 642 muscle contractions (Nc) from 270 consecutive patients (Np) who underwent EMG at our laboratory (software Dantec Keypoint, QEMG) from May 2015 to September 2016 and had interference patterns obtained from at least one of the following muscles: triceps-lateral head, brachioradialis, extensor digitorum communis and biceps. Statistics were calculated separately for normal and neurogenic muscles. Peak(T/A) was calculated by the built-in "peak ratio" function. T/Amax was calculated by the built-in Interference Pattern analysis function. The ratio with the highest amplitude was selected as T/Amax. Linear regression models provided high Pearson correlation coeffficientscoefficients (R) between peak(T/A) and T/Amax for all 4 muscles, normal or neurogenic, except a subgroup of biceps in patients aged <40y. Specifically, R were: (A) triceps normal 0.79 (Nc = 99), neurogenic 0.83 (Nc = 50) (B) brachioradialis normal 0.81 (Nc = 84), neurogenic 0.78 (Nc = 66) (C) extensor digitorum communis normal 0.72 (Nc = 92), neurogenic 0.73 (Nc = 61) (D) biceps (age > 40y) normal 0.77 (Nc = 77), neurogenic 0.67 (Nc = 62). We conclude that T/Amax has a strong linear association with peak(T/A) and, therefore, the former may be further investigated as a potentially useful quantitative diagnostic marker, especially in cases where the latter is not available.

Fasciculations in nerve and muscle disorders - A prospective study of muscle ultrasound compared to electromyography

OBJECTIVES

We examined the clinical utility of muscle ultrasound (MUS) in detecting fasciculations in patients with nerve and muscle disorders (NMD) and investigated the impact on diagnostic sensitivity when combining electromyography (EMG) and MUS.

METHODS

We included 58 consecutive patients suspected to have NMD and 38 healthy subjects (HS). Patients and HS underwent MUS in 14 skeletal and two bulbar muscles and the video recordings of the MUS were anonymised. Only patients underwent EMG.

RESULTS

The follow-up diagnoses were: 15 Amyotrophic lateral sclerosis (ALS), 15 polyneuropathy, 14 patients had other diagnoses (disease-control group) and 14 patients had no pathological findings. MUS detected more muscles with fasciculations among ALS patients compared to all other groups. In ALS patients, the dominating pattern of fasciculations was continuous (45%). More proximal muscles showed fasciculations among ALS patients compared to all other patient groups. MUS was more sensitive than EMG in detecting fasciculations (58% vs. 48%). When combining the two methods, the sensitivity in detecting fasciculations increased to 65%. Fasciculations in nine muscles could predict the ALS diagnosis with high sensitivity and specificity.

CONCLUSIONS

MUS is a sensitive tool in detecting fasciculations in patients with NMD and performs well compared to EMG in diagnosing ALS.

SIGNIFICANCE

MUS may add valuable information in the clinic, especially in diagnosing ALS.

Implications of Synkinesis in Unilateral Vocal Fold Paralysis

Objectives

In patients with unilateral vocal fold paralysis (UVFP), laryngeal electromyography (LEMG) occasionally observes synkinesis in laryngeal muscles, a condition that could impair vocal fold mobility and voice control. This study aims to evaluate the impact of synkinesis on UVFP patients.

Study Design

A retrospective case-control study.

Setting

Medical center.

Subjects and Methods

Patients with UVFP onset >6 months were recruited (N = 104). The outcome measurements included LEMG, quantitative LEMG analysis of thyroarytenoid–lateral cricoarytenoid (TA-LCA) muscle complex, glottal gap measured by videolaryngostroboscopy, voice-related quality of life, and voice acoustic analysis.

Results

According to the LEMG analysis, 8 patients (8%) had synkinesis, and 96 (92%) did not. In the synkinesis group, TA-LCA turn frequency in the lesioned side was comparable to that in the healthy side ( P = .52). Patients in the synkinesis group had higher TA-LCA turn frequency ( P = .001), higher probability of cricothyroid muscle dysfunction ( P = .04), and better voice-related quality of life ( P = .01) but objective voice outcomes comparable to those in the nonsynkinesis group.

Conclusions

Patients with synkinesis will have near-complete restoration in TA-LCA turn frequency but still experience voice impairment, a finding that is compatible with the mechanism of aberrant reinnervation. However, patients with synkinesis have better disease-related quality of life than do those without synkinesis.

Neurophysiological approach to disorders of peripheral nerve

Disorders of the peripheral nerve system (PNS) are heterogeneous and may involve motor fibers, sensory fibers, small myelinated and unmyelinated fibers and autonomic nerve fibers, with variable anatomical distribution (single nerves, several different nerves, symmetrical affection of all nerves, plexus, or root lesions). Furthermore pathological processes may result in either demyelination, axonal degeneration or both. In order to reach an exact diagnosis of any neuropathy electrophysiological studies are crucial to obtain information about these variables. Conventional electrophysiological methods including nerve conduction studies and electromyography used in the study of patients suspected of having a neuropathy and the significance of the findings are discussed in detail and more novel and experimental methods are mentioned. Diagnostic considerations are based on a flow chart classifying neuropathies into eight categories based on mode of onset, distribution, and electrophysiological findings, and the electrophysiological characteristics in each type of neuropathy are discussed.

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.

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.

Influence of spontaneous activity on peak-ratio analysis

OBJECTIVES

To prove or disprove this assumption that in neuropathy patients with abundant spontaneous activity, peak-ratio interference pattern analysis may lead to false negative results.

METHODS

Spontaneous activity >100 microV, automatically analysed by turn/amplitude analysis and expressed as (turns/second)/2 ((T/S)/2), and interference patterns, analysed by the peak-ratio technique, were recorded, one after the other, from the right anterior tibial muscle of 21 patients with neuropathy, aged 36-87 years.

RESULTS

The mean number of spontaneous discharges ((T/S)/2) was 12.3 (range 5.5-26) and its mean amplitude 261 microV (range 146-478 microV). Despite this abundant spontaneous activity, peak-ratio analysis was neurogenic in 81% of the patients. All peak-ratio parameters were independent on the amount and amplitude of spontaneous discharges.

CONCLUSIONS

Spontaneous discharges >100 microV could be adequately assessed by means of the turn/amplitude analysis and did not influence peak-ratio analysis in neuropathies.

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.

Needle EMG of the tongue: motor unit action potential versus peak ratio analysis in limb and bulbar onset amyotrophic lateral sclerosis

OBJECTIVES

To find out if conventional and automatic needle EMG of the tongue can be helpful in the diagnosis and differentiation of limb and bulbar onset amyotrophic lateral sclerosis.

METHODS

Motor unit action potential (MUAP) analysis and peak ratio interference pattern analysis were performed in the right genioglossus muscle of 30 healthy subjects aged 30-81 years, 10 patients aged 49-73 years with limb onset amyotrophic lateral sclerosis, and eight patients aged 52-75 years with bulbar onset amyotrophic lateral sclerosis. Electrical activity was sampled via standard concentric needle electrodes with a commercially available EMG recorder.

RESULTS

Normal mean (2SD) MUAP duration was 6.6 (1.5) ms. Normal mean (2SD) MUAP amplitude was 224 (97.4) microV. Normal mean (2SD) peak ratio (PR), turns/second (T/s), amplitude/turn (A/T), and time intervals (TI1, TI2, TI3) were 1.68 (0.56), 732 (303.9), 446 (180.3) microV, 2.62 (0.34), 2.31 (0.14), and 1.01 (0.50) respectively. Mean MUAP duration and amplitude were significantly increased in limb onset (P=0.0001 and P=0.013) and bulbar onset amyotrophic lateral sclerosis (P=0.0001 and P=0.017). Peak ratio indices stayed unchanged in limb onset amyotrophic lateral sclerosis but were significantly decreased (PR, T/s, A/T, TI1, and TI2) or increased (TI3) in bulbar onset disease. The sensitivity of the MUAP analysis was 70% in limb and 75% in bulbar onset amyotrophic lateral sclerosis. The sensitivity of the peak ratio interference pattern analysis was 20% in limb and 100% in bulbar onset amyotrophic lateral sclerosis. Subclinical involvement of the tongue was found in 20% of the patients with limb onset amyotrophic lateral sclerosis and could be more accurately assessed with MUAP analysis than with automatic EMG.

CONCLUSIONS

Both conventional and automatic needle EMG of the tongue are valuable electrophysiological devices to assess the clinical and subclinical involvement of the tongue in patients with limb and bulbar onset amyotrophic lateral sclerosis.

Electromyography in myopathy

Electromyography (EMG) is the most common procedure for screening patients with myopathies and remains the most important technique for assessing the course of the disease over time. Fibrillation potentials, positive sharp waves, myotonic or complex repetitive discharge, as well as polyphasic potentials are non specific and can occur in both myopathic and neurogenic lesions. The most sensitive and specific parameter for myopathy in conventional EMG is the decreased duration of motor unit potentials (MUP), but this can also be seen in disorders of the terminal motor fibers or the neuromuscular junction. More advanced techniques such as single fiber EMG, macro EMG, scanning EMG and turns/amplitude analysis have opened additional possibilities for analysis of the motor unit and the interference pattern, by which both the sensitivity to early changes and specificity for myopathic alterations is increased. The importance of combining different techniques to improve diagnostic yield and specificity is stressed.

Turns-amplitude analysis assessment of myopathies in HIV-infected patients

Electromyographic interference patterns during a gradual increase in force were studied by means of the turns-amplitude analysis in a series of HIV-infected patients with and without clinical, biological and histological signs of myopathy. Different parameters were evaluated to determine their sensitivity for the diagnosis of the myopathies that occur in this context. The studied parameters were the number of turns (NT), the mean amplitude of the turns (MA) and the ratio NT/MA (RTA). For each parameter, we compared the interest of mean values, calculated at moderate contraction, to that of peak values. In addition, the shape of the cloud of MA plotted versus NT data points was analyzed. The sensitivity of the turns-amplitude analysis was 95% for the diagnosis of myopathy when NT, MA and RTA were taken together into account, versus 80% in the cloud studies. Peak values were the most sensitive criteria, but mean values abnormalities were observed in some cases of zidovudine myopathy, indicating a potential usefulness of this quantitative EMG method in the differential diagnosis among myopathies in HIV-infected patients.

Neural network analysis of the EMG interference pattern

This paper investigates the performance of artificial neural networks for analysing and classifying EMG signals from healthy subjects and patients with myopathic and neuropathic disorders. EMG interference patterns (IP) were recorded under maximum voluntary contraction from the right biceps of a total of 50 subjects. Parameters were obtained from the signals using recognized quantification techniques including turns analysis, small segments analysis and frequency analysis. Supervised networks examined were an improved backpropagation network (IBPN), a radial basis network (RBN), and a learning vector quantization network (INQ). Supervised networks using different combinations of parameters from turns analysis and small segments analysis gave diagnostic yields of 60-80%. Combinations using frequency analysis parameters produced similar results. The performance of unsupervised Self-Organising Feature Maps (SOFM) was generally lower than that of the supervised networks. Including personal data (sex and age) did not improve the overall performance.