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These Forums are no longer active. We have maintained some of the frequently asked questions and answers for educational purposes.

30-40% false negatives results in EMG

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

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 insterted in EMG?

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.

Sedation for infants during EMG NCV testing

My 16-month-old daughter was born with a left clubfoot, and bilateral PIP contractures of digits three and four. We were told she has distal arthrogryposis. The clubfoot did not correct completely with casting and bracing. She will be having surgery. The neurologist wants to rule out muscle and nerve disorders first. Can she be sedated for this test? Will the results be accurate?

Answer

Sedation, most often, is not needed for EMG because the test is tolerable and the muscle voluntary contraction is required which cannot be done under sedation. However, the doctor should be able to assess this need. The EMG in your child should give useful information about the status of the muscles and nerves.

Comment

Thank you for your reply. My daughter has a tremendous fear of doctors. In fact, we were unable to get x-rays of her foot, because she was so afraid of the technician and cried and climbed off the table etc...Therefore, knowing her, she won't cooperate at all. I feel the only way is to sedate her. How much of the test will be reliable if I do? Will she wake up from the sedation when the electricity goes through, or when she feels the needles? Thanks!

Answer

Thank you for your email. Usually the doctors and technicians in EMG have their own kind way of dealing with patients from all ages, even infants. Therefore, I would not expect real difficulty during the test. However, the sedation does not affect the results of nerve stimulation. If she awakens during the test, it does not affect the result, even if there is a little pain or discomfort.

What is difference between acute and chronic? And does temperature effects NCV?

Results of my EMG/NCS - Right lower extremity Temp = 33.3C Conductions. Sensory conduction velocities at the lower end of normal, but within normal in the leg with normal amplitude. Motor conductions at the lower end of normal, but within normal with normal F-waves in the lower 60's. - Needle exam Evidence of chronic low-grade denervation with increased numbers of polyphasic appearing units, but no significant giant units. Complex repetitive charges are noted in abductor hallucis and abductor digiti minimi pedis in both feet, and rare myokymia in abductor hallucis in right. No significant evidence of acute or chronic denervation is seen in more proximal musculature. Significant fasciculatory activity in seen in intrinsic foot muscles and in calf and anterior compartment muscles, slightly more prominent in the calf muscles than in the anterior compartment musculature. -Right upper extremity Temp= 33.6C Minimal slowing of sensory nerve conductions distally in the hand with conduction velocities in the low 40's. Motor conductions in the upper extremity are normal with normal F-wave latencies. I've had fascics for, probably, 15 years. No weakness at all. Docs don't have a clue except a diagnosis of a 'neuropathic process with fasciculations and minimal nerve conduction abnormality, but needle exam findings suggest a very slow and indolent motor axonal process'. I think they are referring me a Boston NM expert. A couple questions..... 1) What is difference between 'acute' and 'chronic'? 2) Were the temps in foot and hand low for this type of test? 3) I gather low temps can impact conduction velocities. Is it correct to assume that needle exam is relatively unaffected by temp. 4) Any of this look at familiar? They seem to think I was pretty unique.

Answer

In answer to your questions: 1) In needle exam terminology, acute means the presence of fibrillations and positive waves, usually indicating that the nerve injury is recent, more than 2 months and less than 2 years (these are approximations). Chronic means at least 6 months old (acute and chronic may coexist for a while) and indicates that the nerve has begun to regenerate and reinnervate the muscle. 2) The temps are within acceptable range 3) Generally speaking the needle exam is unaffected by temp except for fascics which may be decreased or altogether suppressed by low temps. 4) It is difficult to give an impression on the net. Findings such as yours can be seen in peripheral neuropathies. However such a diagnosis does not account for the fascics or the myokymias. I think a neuromuscular specialist who can put this together with the clinical symptoms would be of help.

Current Perception Threshold test

What is the current perception threshold test? Does it replace EMG

Answer 1

I am not quite sure what the Current Perception Threshold test is. It certainly does not replace an EMG. If you have more info on it, I would be happy to tell you more.

Answer 2

Perhaps this test is similar to the "Sensory Test" given at my medical institution. Ours involves testing for light touch, vibration and hot/cold sensitivity. I don't believe that our testing includes any minimal electrical current perception, but I suppose this variation may exist.

Answer 3

I think as the name implies, this technique should be able to perform "non-invasive" and provides a kind of measure of sensory function using special surface probe. By all means as pointed out, it does not replace the nerve conduction or EMG studies.

Breathlessness encountered after EMG test

I would love to hear an opinion on a situation my mother recently encountered after having an EMG Test/NCT. She has had difficulty breathing since the day she had her test. This has continued for about one week now. She says she is experiencing "breathlessness". It started the evening after the test. I would appreciate any feedback on this situation.

Answer

I am assuming that EMG/NCS was performed for extremity nerves. In this case the test by itself does not cause "breathlessness". Therefore, my advice to see internist for her symptoms.

Comment

Thanks very much for responding. It was performed for persistent neck, back and leg pain.

Epileptic fits started after EMG test

I had a needle EMG to see if I had carpal tunnel syndrome and ulnar nerve entrapment, The test was very painful. I felt terrible shocks through out the test. I told the dr. how painful it was and he said we were almost done, well the last needle was inserted in the back of my head, very near the top of my spine, well the shock felt like I was being electrocuted. Immediately after that I was unable to speak without stuttering for at least one month. When it finally stopped my body was like having terrible convulsions. Finally that stopped and I started having seizures. Grand mal type. Now three years late I am diagnosed with epilepsy and I must take tegretol xr 6 times a day. What I need to know is if anyone heard of this happening before. I see a neurologist every 4 to 6 months and he said he doesn't know. I never had seizures before this and they are not in my family also I didn't sustain any other injury, except for getting my hand crushed months earlier. Please help me find out.

Answer

Seizures are caused by injuries (trauma, congenital, vascular etc..) to the central nervous system or can be due to metabolic disorders. EMGs come nowhere near any of the above and seizures are not known complications of an EMG exam. The timing of your episodes and the EMG exam is understandably curious, but the connection between the two can't be made because of what I described above.

Is it necessary to move the needle inside the muscle during EMG exam?

I had needle EMG today. The Dr performing it, after every needle stick, moved the needle around roughly causing a lot of discomfort, is this something done with every stick; he also had me flex my foot when he was sticking my leg. I do understand that the nerve pain is at the insertion of the needle but to continually move the needle around after insertion, is that necessary. At times he scraped the needle back and forth after he inserted it, is this normal for this procedure. I thought when you are testing the activity of the muscle you have to have the needle still after insertion. I have had EMG before and it was nothing like this one. I ask the Dr. if I could see the results on the screen and he said he did not save any of it and showed me another pt's results that was positive for nerve damage. He told me not to pursue nerve damage any further. Thank You

Answer

It is part of needle EMG to move the electrode inside the muscle, also to ask the patient to activate the muscle against resistance. This is quite normal procedure. However, the test is varies between the examiners and type of request for the test. However, the pain is short lasting and leaves no squeal.

EMG Procedure?

I am new to the world of EMG's but have been ordered by my doctor to have one after an epidural went bad. How long do they normally take? Is there a physical before? Would I need to bring any information? How many needle insertions are normally in each leg, (which I am having done, lower leg nerve damage) and what other procedures are done along with it? I was freaked after the epidural went wrong, so this would all help to calm my fears.

Answer

The time of the EMG is variable depends on the patient but usually 30 minutes. You do not need to do physical activity before. The number of insertions again variable, the electromyographer decides that. The study consists of two parts, the nerve conduction studies, you would feel some electrical impulses stimulating the nerves causing movement of the muscle, it causes little but variable discomfort. Then the second part is the insertion of the needle electrode into the muscles (feeling of little prick). Both tests are put together to see whether your nerves are affected and how much. It is very useful and sensitive tests.

Thigh pain after EMG

I just had an EMG done, and ever since then, I have had some moderate to severe pain in my left thigh. I had no pain there before the test, which was quite painful. The doctor who performed the test doesn't know why I would have this pain. Is this a common side effect of the EMG? If so, how long can I expect it to last? Any help you can give is greatly appreciated, and I look forward to hearing from you.

Answer

The pain or discomfort at the site of EMG insertion may last minutes and up to few hours and very rarely up to 24 hours. If it is longer or moderate to severe, another cause should be looked for. However, you did not mention how long you have this pain following EMG and why, to start with, EMG was performed?

EMG and Plaquenil

I am scheduled to have an EMG. I am currently on Plaquenil from a former doctor. The Rheumatologist told me to stop taking the Plaquenil because it could interfere with the EMG results. Is this true? I asked this question on the neurology forum and the doctor said they never heard of such a thing.

Answer

It is true that Plaquenil (Chloroquine) has neuromuscular side effects; muscular weakness or neuropathy, usually with long-term treatment, among other complications. The point, I do not know why EMG was requested?, perhaps, to check that this drug is not affecting your nervous system. If affecting, then you should discuss it with your doctor to discontinue or give alternative medication. Please update me if you wish.