EMG Techniques - Part II

Single proximal conduction block, significance? Top

Question

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” Top

Question

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 Top

Question

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! Top

Question

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

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???)

THANK YOU FOR READING THIS AND I WOULD APPRECIATE YOUR INSIGHT!

Answer

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

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” Top

Question

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 Top

Question

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?  Top

Question

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.

30-40% false negatives results in EMG  Top

Question

In your answer to a previous post you stated that some studies have indicated that needle EMG can give false negatives 30-40% of the time in detecting a root lesion.

Why is this? Also does this apply strictly to testing for radiculopathies or other disease processes as well?

Answer

Yes, thanks for the clarification; the 30-40% false negatives in the studies I quoted applies only to radiculopathies.

This is due to many factors, including the fact that while radiculopathies may be painful, they may actually not cause any nerve damage (which is what is picked up by the needle exam of the muscle), sampling or interpretation errors, detection error due to poor relaxation, timing of the exam etc..

Comment

Are there any general statistics in regard to false negatives or diagnostic accuracy in general for EMG? Or are there statistics for individual disease processes such as neuropathies, myopathies etc?

Answer 1

Well, generally speaking, in compression or entrapment neuropathies (such as Carpal Tunnel, Ulnar, Radial or Peroneal Neuropathies, or Bell's Palsy), the yield is pretty high (I do not have numbers) even though there are still false negatives. In root lesions, as I mentioned before, the yield drops, as it does in neuropathies and myopathies, probably again in the 30-40% area. EMG is considered to have the highest yield in entrapment/compression neuropathies.

Answer 2

I would like to tackle this point by talking about how the electrodiagnosis contribution to diagnosis of myopathies in form of false positive or false negative. First of all, it is important to keep in mind, unfortunately, that none of the abnormalities in EMG is pathognomonic or specific for any single myopathic disease. Second, EMG is important but general guide to diagnosis, but we should keep in mind again that exceptions do occur. Now, the question, could EMG be false positive in myopathies? The answer is yes, due to technical reasons (MUP measurement, over-reading), also it can be false negative, due to again technical reasons (MUP measurement, simply missing mild changes) or mistaken the changes to be due other cause. Regarding neuropathy, again, false positive can occur due to technical reasons, temperature and age. While the false negative can also be due to some technical reasons in the recording.

Best time to perform EMG  Top

Question

My physician has referred me for an EMG. He has advised that I wait until I am symptomatic. I want to be sure I schedule it at the best time. My symptoms relapse and remit lasting for about a month with a two-month downtime between. I have: numbness and tingling in extremities, my knees buckle, vision disturbance, short bouts of tremor in arms, tightness in knuckles of fingers and toes, slight difficulties with fine motor skills in fingers--hesitancy, impaired balance. Last time, I even had a brief bout with facial paralysis (around my mouth) and difficulty swallowing.

The visual and numbness/ tingling symptoms are the most constant, the others can last anywhere from a couple hours to 5 days. Which symptoms will assure the most thorough results from EMG testing?

Answer

The only time it makes a difference to be symptomatic or not for an EMG is when a doctor is suspecting diseases of neuromuscular transmission such as myasthenia gravis, because the findings do tend to vary. For other diagnosis such as peripheral neuropathy (causing the numbness or tingling) or entrapment or compression neuropathies, the general rule of thumb is that if you have a lesion there, it would be positive on EMG regardless of the timing of symptoms. So it is important to know what your doctor is suspecting before you decide to wait until symptomatic or not to have the study.

Comment

I think my doctor suspects a neuromuscular origin for my problems. Which symptoms (described earlier) would be most sensitive for testing? I.e. would a day with say vision disturbance, intermittent knee buckling and jerky pinky movements is a better day than just one with lots of tingling, balance and vision problems?

If I am experiencing newer symptoms would they show up less than symptoms that have repeated?

Answer

Yes usually neuromuscular transmission problems manifest themselves primarily in visual disturbance (double vision or droopy eyelids) and fatigability. So the days that these symptoms are worse will probably be better days to be tested.

Comment

I am experiencing my 3rd month-long attack. Will older symptoms show up better than new ones?

Answer

Probably so.

Comment

It appears after doing some checking, that having an EMG + NCS while symptomatic will be logistically impossible because they cannot be scheduled on short enough notice.

I have described my relapsing and remitting symptoms in previous posts. While I think my doctors would like to rule out problems of neuro-muscular origin, they lean much more toward CNS disorders at this time.

I have difficulty believing that if I have this testing done while I am symptom-free and my nerves are functioning normally, that the EMG will be able to pick up the problem.

How successful are the tests at recognizing difficulties like I've described?

How deep should the needle be instead in EMG? Top

Question

Is it important to insert the entire needle to the muscle?? The doctor who did my EMG told me that the active part is in the tip of the needle...

Answer

Enough part of the tip and the cannula need to be in the muscle to appropriately record the signal.