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Electronic EMG Manual®
Peripheral Nerves Anatomy
General Muscles Anatomy
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Needle EMG Anatomy Atlas
Patient Education Series (FAQ)
Nerve Entrapment Guide
  Evidence of Re-Innervation in EMG findings  
  In terms of reinnervation findings of EMG, including increased recruitment, instability of MUP, increased Amplitude of MUP (?), etc, which of these features are reliable to predict the true re-innervation in morphology? The reasoning process of EMG physiology is not specific to predict morphological changes.  
  Answer 1 One of the first things to appear after denervation is fibrillations and positive waves of course. Following that (in about 2 months) the first signs of reinnervation are an increase in the number of phases of a motor unit, polyphasic potentials (check out: http://www.teleEMG.com/jbr120.htm Neurogenic Motor Unit), and increased instability of the MUAP (high jiggle) with decreased recruitment followed by an increase in the amplitude.
  Answer 2 Further comment on evidence of reinnervation in addition to concentric EMG findings. The Fiber Density (FD) increases after reinnervation due to collateral sprouting. The increase of FD indicates that muscle fibers increased for the same motor unit. The FD therefore, is a most sensitive method to quantify reinnervation, and therefore, the local organization of motor unit (morphology!). Also, FD corresponds to type grouping in pathology.
  EMG Technique (fasciculations)  
  Is there a way to distinguish between benign and malignant fasciculations ELECTROMYOGRAPHICALLY and most of all CLINICALLY? Is it true that rhythmic fasciculations tend to be benign while a singular big thumps tends to be malignant? is it true that brief fasciculations tend to be benign. Is it true that coarse fasciculation are usually benign while the malignant ones are very fine ones? What of all that is true and how it reflects in EMG.  
  Answer 1 This is a very common concern and generally no single answer is satisfactory because almost every single rule you make to define a benign versus malignant fasciculation has an exception. Generally speaking though I can tell you that Neurologists rely on far more than the presence (or absence) of fasciculation potentials to make the diagnosis of ALS. If fasciculations become worrisome to a patient, I generally recommend they seek a qualified neurologist's opinion to ease their fears, because the worst thing they can do is to self diagnose them with the disease.
  Answer 2 The best measure of benign versus malignant fasciculation potentials comes from the EMG needle exam by the company they keep...in other words... if fibrillation potentials and positive sharp waves are present with large motor unit potentials and polyphasic waveforms with poor recruitment...along with fasciculations...this would tend to suggest a more ominous potential...A good history and physical exam is a priority...remember an EMG exam is only an extension of our physical examination.
  Single Fiber Amplifier Settings  
  I am having a minor debate on Amplifier settings for SFEMG. (I believe the Filters were changed on my system.) What are the recommended settings and have there been any recent changes in them? Specifically, I am concerned about the Low Frequency Filter Setting. What would be the upper limit? What is the typical setting?  
  Answer The recommended or typical filter settings are LFF 500 Hz and HFF 10 KHz. I may use LFF 1KHz (narrower settings). This LFF setting would reduce the disturbing distant muscle fibers. This setting, however, affects the shape of the single fiber potential. But it should not affect the jitter value or fiber density reading. I am not aware of recent changes. However, if detailed measurement is needed for the shape of action potential, then use more open filter settings LFF 2 Hz and HFF 20 KHz.
  Theoretical guidelines vs. practical for thoroughness of EMG studies  
  Having read the guidelines in the online EMG manual for the thoroughness of the study of a muscle (i.e. testing 20-25 units for both spontaneous and voluntary activity, calculating average amplitude phase etc.) I am curious why it seems these guidelines aren't followed more often. Having had a number of EMGs in the past year in both local and university settings and in all cases only 3-4 units (1 insertion 3-4 directions) was sampled. One of these EMGs was overseen by a very renowned name in Electromyography (no names, but odds are you have one of his books on your shelf,) and even then 1 needle insertion per muscle. In a dialog with a doctor who does follow these guidelines, I was told many of the patients he performs EMG on tell him that his study is far more thorough than that done by their own neurologist. I fully understand the reasoning behind the 20-25 MUP guideline if for no other reason than to increase diagnostic accuracy. My questions then are twofold. Do most Electromyographers routinely follow these guidelines or are they followed only when the situation/case dictates. Secondly, how much diagnostic accuracy is there when only 3-4 units per muscle are tested, for example during a MND workup, and no abnormalities are found?  
  Answer I agree not all EMGers follow these guidelines, although I do catch myself sampling less frequently in follow-up studies when I am only looking for changes.
  Comment My EMGs have been done locally. I certainly understand your comment about less stringent testing when verifying a change. My main concern is with initial testing where the results are negative, no sign of any disease process. With what degree of certainty can the electromyographer state that the muscle tested is normal when only testing 3-4 units in that muscle? Are they any statistics or figures on how the number of units sampled in a muscle corresponds to diagnostic accuracy rates? I can calculate numbers based on basic probability theory but was curious if any formal studies or accepted statistics existed. Thanks again and kind regards.
  Answer Tough question to answer. I don't know of any studies of predictive statistics (for the number of muscles tested vs. diagnostic accuracy rate) That would be an interesting study. As for number of units tested, naturally if you find the abnormality in the muscle early on (with 3-4 units), you don't need to go any further. But if you don't, the general rule of thumb is to be more thorough to increase your chances.
  Answer 2 I agree it would be an interesting study. From a strictly mathematical perspective it should be fairly easy to compute the "odds" of finding abnormalities. This is a lot like the classic probability problem of given that a person throwing darts can hit the bulls eye x% of the time, how many times must they throw the dart to have a given percent chance of getting a bulls eye. In the case of EMG the "x" can be the percentage of units in the muscle involved in the disease process. The number of throws would be the number of units tested and percent chance of getting a bulls eye would correspond to the odds of hitting an involved unit. The equation for this would be: ln(a) = ( ln(i)) / (n)) In this equation the variables are: a - the percent chance of hitting an involved unit expressed as a decimal (i.e. 56% = .56) i - the percentage of units in the muscle involved in the disease process as a decimal n - the number of units sampled in the muscle I have made several assumptions in this equation. 1. The involved units are randomly distributed throughout the muscle. 2. When the needle hits an involved fiber, the pathological signs such as fibs, positive waves, polyphasic units etc. will be visible to the EMGer. 3. The insertion points will be randomly distributed across the muscle. This is not entirely accurate since there would probably only be 4-5 actual insertions through the skin and then testing in multiple directions to get the 20 units. However assuming the insertions were not all done in the same spot, the equation holds. The results of this calculation clearly show why sampling more units can yield more accurate results. Examples: Sampling 20 units in a muscle with 10% involvement gives you a 90% chance of finding an involved unit Sampling 4 units in a muscle with 10% involvement gives you a 56% chance of finding an involved unit. Sampling 20 units in a muscle with 25% involvement gives you a 93% chance of finding an involved unit. Sampling 4 units in a muscle with 25% involvement gives you a 70% chance of finding an involved unit. Sampling 20 units in a muscle with 50% involvement gives you a 97% chance of finding an involved unit. Sampling 4 units in a muscle with 50% involvement gives you an 84% chance of finding an involved unit. So sampling more units in a muscle greatly increases the chances of finding an involved unit, especially early in the disease process. Kind regards
  Answer 3 I read the interesting discussion on this point. I believe that few additional factors may influence the number of motor unit tested. Firstly, the experience of the neurologist or electromyographer. Secondly, the clinical examination of the patient. And finally, the degree of patient's cooperation during sampling. It is also, basically, the same argument could be applied to the number of F-waves should be obtained for shortest latency. My kind regards,
  Answer 4 Very interesting subject. About 4 years ago I was in Italy / Milano/. At the very famous S.R. Hospital I saw the following practice. The electromyographer there does not catch even one potential at single muscle. They say to the patient to do a slight effort, then observe moving potentials (do not record), after e period of few minutes they made conclusions e.g. MUP with growth of amplitude and area. I asked them how long of a period is needed to become proficient in this method: - 3 months  
  Single proximal conduction block, significance?  
  How significant should a single or isolated motor nerve proximal conduction block be as diagnostic sign, for instance in multifocal motor neuropathy, inflammatory demyelinating polyneuropathy or the "new entity" the multifocal inflammatory demyelinating neuropathy. Occasionally, I come across such an isolated finding, rechecked to exclude technical.  
  Answer No single "isolated" abnormality should be diagnostic for a specific lesion. What is the waveform morphology? Abnormal temporal dispersion is usually absent in MMN. "Inching" along the course of the nerve often can demonstrate if the CMAP diminishes abruptly as in MMN, or progressively as in chronic axonal loss or demyelination. What clinical signs are present upon examination? Asymmetric distal weakness generally is present in MMN versus symmetric, proximal weakness in CIDP. The presence of a single proximal conduction block across common sites of entrapment is not helpful in establishing a diagnosis of MMN.
  NCV “latency”  
  The Latency that is measured: 1.Does it depend on the distance taken by the examiner? 2.Does it depend on the amount of electric stimulation (such as the CMAP amplitude)? 3.Is it better when high or low?  
  Answer Yes, the latency depends on the distance, the greater the distance, the longer the impulse has to travel and the greater the latency. It also depends on the amount of electricity you use; if you are submaximal, you are not stimulating all the fibers and your measurement will be inaccurate. That's why in nerve conduction it is advised that you use supramaximal stimulation which is maximal stimulation + 25% over that to ensure stimulation of all the nerve fibers.
  Timing of benign vs. pathological fasciculations  
  One small question, in your electronic EMG manual you state that benign fasciculations generally occur at 8-second intervals whereas pathological ones occur at a slower rate of 3.5 seconds. In another online resource that has video files of EMG findings: http://www.med.ohio-state.edu/physmed/videos/EMGvideos.html They say the opposite, "Non-pathologic fasciculations usually recur at a very slow rate (less than 3 per 10 seconds), while pathologic fasciculations most commonly occur more frequently than 3/10sec." While I know that without other EMG findings (or lack of) it is tough to say one way or the other if fasciculations are good or bad but I am curious about these different viewpoints. Thanks again for providing such a valuable resource!  
  Answer I am aware of the discrepancy in the literature on benign vs. malignant fasciculations. Over the years, I find myself no longer regarding this as black and white but rather find myself relying more heavily on many factors such as the shape of the fasciculation potential their distribution and what else I am finding. For instance, the more complex and "polyphasic" the morphology, the more likely I am to consider them pathological (I don't like the term "malignant"). Other factors that enter my mind is their widespread distribution and the presence of other signs of ALS such as fibs and positive waves and neurogenic units. So I now rely on the "environment" in which I find the fasciculations rather than on one or two factors alone. Thanks for your kind words.
  Comment Thanks for the reply. I understand your point about what else you find being the true diagnostic criteria. I am curious though which theory is "supposed" to be correct or is there no real consensus?
Also if it isn't too complex what is the reasoning behind one being "slow" and one being "faster?"
Again thanks for taking the time to help not only me but all the people who come here with questions. With kind regards,
  Computer assisted EMG!  
  I know that some of the neurologists use computer program for the analysis of EMG needle insertion results. However, I am not sure how advanced these computer programs are! In my EMG exam I got the results within minutes after it ended (normal) and the neurologist told me that his computer program makes much of the analysis for him rapidly - for example MOTOR UNIT ANALYSIS! He said this advanced program analyzes the motor units! MY QUESTIONS ARE: 1.Does it sound possible (motor unit analysis done by a computer program? 2. some of the results of a muscle were (motor unit) (tibialis anterior) AMP (normal), Duration (normal), poly (normal) STABILITY (normal) INTERFERENCE PATTERN (normal) Is there any computer program that can analyze these features of MUP "alone" - I mean check these MUPS features for the neurologist without he analyzing it by himself? MY question refers mainly to motor unit stability (but also AMP, duration, IP and poly) - can the computer check if the MUAPs are STABLE without the neuro "doing this job", can the computer tell by "itself" the motor units are stable and not polyphasic?  
  Answer 1 It is amazing what computers can do. I think we have not seen anything yet, still more to happen in the future. I can recall an American association of EMG and Electrodiagnosis session in 1984 about role of computers in EMG by Joe Jabre and David Hampton. The Computer program was able from that time to perform MUP parameter analysis. The software is getting better. The point that the computer is willing to help but I think working experienced human brain is always needed to rectify the technical problems, for instance, quite frequently you need to correct the position of markers during MUP analysis otherwise you may end up having false prolonged polyphasic unstable MUP.
  Answer 2 Thanks for this interesting question! The truth is computers have come a long way since the early 80's and can "assist" EMGers a great deal but not make diagnosis. There are still a lot of things that an experienced EMGer can pick up that can be missed by the computer. More importantly if the recording electrode is not placed in the appropriate area of the muscle, you feed poor quality data to the computer and as the saying goes "garbage in, garbage out". So yes computers can be very helpful but no they are not smart enough to replace humans.yet.  
  Comment I know computerized EMG is of great value! Your insight on this fascinating use of computers will be highly appreciated! My question is: (using the most sophisticated computer programs) - does the computer calculates and prints out specific answers or just "normal"/"abnormal" - for example MUAP A. Stability - does its output is: "normal stability"/ "reduced stability",/"slightly reduced" or just "abnormal stability". And for B. amplitude and duration - can the computer calculate them and "decide" by its own - whether these are within normal ranges? C. And what about the IP - can it "distinguish" several levels of reduced IP or it can just decide "normal/abnormal"? * I would appreciate your insight on these 3 features of the computer analysis (stability,amp-dur and IP) * when It does this MUPS analysis by "ITS OWN" how many motor units does it check (10,20,30,40) How much time does it take for it to check this number of MUAPs (seconds???)
  Answer 1 Yes the computer does all those functions, but of course with manual help i.e. operator should accept/reject the potentials. The system can take any number of MUPs, the operator should again decide that number.  
  Answer 2 This is a very general question as you can gather and different machines have different programs for different tests so it is impossible to answer this in a "wholesale" fashion. However, as far as motor unit analysis is concerned, most programs used usually give printouts of measures (numbers) for amplitude, duration and number of phases and some do firing rate analysis. Some do Turns and Amplitudes analysis. Some of these numbers are generated as numbers and some are plotted against a "cloud" of normal reference values and those, which fall outside the cloud, are called abnormal. Generally speaking, and realistically, only 5-6 different motor units can be properly analyzed from one needle location, because, as more motor units are recruited, the tracing becomes too complex for the program to analyze and the data generated less reliable. Most programs today on commercially available equipment can reasonably follow a contraction up to 30% of maximum and after that they become unreliable. To do a reasonable computerized motor unit analysis, it usually takes anywhere between 30-45" or up to a minute per insertion.
  Comment It was pleasure for me to have your insight on the computer assisted EMG issue. You said you do not know what program did he use: well, He said this "is the most sophisticated EMG program and that it is able to do mups analysis almost alone!
Yet; another question. What about positive waves and fibrillations- Is the program capable of detecting (distinguish them from other activity) and count them and at last print How many of them there were? (I think HE said it can)
The output of the computer was: (all the insertions) fibs -0/10 PSW- 0/10
What DO these numbers mean? Is there any computer, which can pick up fibs/PSW by its own, distinguish them, count them and print their number without the examiner doing that?
  Answer Sorry, I cannot comment on all the specifics as these vary greatly from system to system and EMGer to EMGer  
  Comment My question is again about the use of computers in a regular EMG test. Is there any computer program nowadays that can pick up fibrillations, count them and distinguish each one of them by its own. And then output for example: "3 fibrillations"? I know that each fibrillation has its own rhythm so that is why I am asking if there is ANY computer program that is able of distinguishing each one of them and of course, recognizing a fibrillation and distinguishing it from any other activity and all by its own?????? (MY main question is about the ability of any computer program to identify and recognize a fibrillation and distinguish it from any activity)  
  Answer 1 In the ones I am familiar with it is the doctor that picks the number of fibrillations he or she sees in the muscle and enters them into a report generation software in the computer which then prints it  
  Answer 2 Although there is none at present time but it sounds like a potentially possible idea to make a computer program to do such fibrillation and PSW detection and counting, similar to spike detection in EEG. Perhaps, it is a matter of time  
  EMG “Interference & recruitment”  
  What about the interference pattern and motor units recruitment?? Is There any computer programs that can "decide"" if the IP was full? What is the output normal/abnormal or it can also distinguish different levels of poor recruitment?? and motor unit stability? What is the output in this case? (stable/unstable or various degrees)? * In my EMG the neurologist told me the computer does mups analysis all by its self within less than a minute per insertion The results were: "stability: normal, IP: normal" and he told me his new computer program can decide and check these two parameters by its own. Is it possible (regarding these two parameters)? And what would be the output (the question above)  
  Answer Again not knowing the specifics I can only answer this question in general terms:

The IP is (usually) studied with a program called the Turns and Amplitudes analysis. This is pretty rapid and can give an idea of the interference pattern. It usually plots the data inside a normal population cloud. If your data is inside the cloud the IP is OK, if it's outside it is not. So the output here is graphic.

Stability is decided upon by what is called a "jitter" between the various components of the motor units, and again, since motor units are only adequately analyzed at a 30% level of maximum, only those which could be appropriately analyzed can be called stable or unstable. So the output here essentially is text

  60 Hz Electric interference  
  When putting the needle (in my EMG) in left triceps, there was a very steady wavy line instead of the normal straight normal line my neurologist just could not reach the desirable wavy line. (I think there was not any sound) - during voluntary activity everything was normal. IT was a steady ("sine like" or "snake like" wave) - I think It was not fibs- because there was no sound and fibs look more like spikes - mine were very very wide "tall", "fat" regular steady waves. They were upward negative (thus, not PSW). And it was so steady. I think I recall He said It was nothing pathological, but an electric disturbance from the background. Does my description sound like such known electric disturbance from the background? What else could it be? And if it is an electric disturbance from the background - Does it have ANYTHING to do with the condition of one's muscle (poorly relaxed for example) because it was normal straight line in the right triceps.  
  Answer What you describe sounds like pure 60 Hz interference from nearby devices or a poorly attached ground. None of that is pathological, just electrical artifact.
  Can EMG test flexibility?  
  Could anyone advice me if EMG can test flexibility and if so are there any references you could give me.  
  Answer 1 Certainly the muscle flexibility is important in sports and athletics. It generally would reduce injuries. In "routine" or the conventional EMG, we do not measure or test for muscle flexibility.
  Answer 2 Routine EMGs cannot assess the flexibility of the muscles rather it is only a diagnostic tool. Flexibility is best measured clinically.  
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