What Medications Affect Nerve Conduction Study?


What Medications Affect Nerve Conduction Study
For example, excess alcohol consumption, hypothyroidism, diabetes, systemic diseases, or neurologic medications such as muscle relaxants, opioids, or psychotropic medications can all affect the results of a nerve conduction study.
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What medications interfere with nerve conduction test?

If an EMG is requested, we ask that you be off of all muscle spasm/relaxer medications for at least 24 hours before your EMG. Common examples of these medications include baclofen, clonazepam, diazepam, alprazolam, lorazepam, and tizanadine.
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What should I avoid before nerve conduction study?

Do not smoke for 3 hours before the test. Do not eat or drink foods that contain caffeine (such as coffee, tea, cola, and chocolate) for 2 to 3 hours before the test. Wear loose-fitting clothing. You may be given a hospital gown to wear.
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Can you take pain meds before nerve conduction?

Nerve Conduction Studies (NCS) and Electromyography (EMG)

NCS and EMG are done to test muscles and nerves. It is an in-office procedure and does not require hospitalization. On average, an EMG takes anywhere between 30 minutes and 2 hours. It can be done at any time during the day. EMG is a test like an EKG or an X-ray. EMG is not a treatment.

Preparation :

Few preparations are needed on the day you have an EMG. Please notify your physician if you are taking a blood thinner (aspirin, plavix, coumadin, lovenox, etc) as there is a chance of bleeding in to your muscles during needle EMG. Please do not apply any lotion, cream or ointment on the day of test. You will be required to change into a gown for the test. You can have regular meals before the test. You can drive yourself.You can go back to work after the test. Take all your medications on the day of the test. If required, you can take pain medication (Tylenol, Motrin) before the test. No sedation is given during the test.

Procedure :

During this test, you will be lying on an examination table, next to an EMG machine (which looks like a laptop or desktop computer). The test consists of two parts. At times one may be done without the other.

Nerve Conduction Studies

The first part is called Nerve Conduction Studies. In this part brief electrical shocks are delivered to your arm or leg similar to a “funny bone feeling”, one gets when the elbow hits a hard surface. The procedure consists of stimulating a nerve and the response is recorded by the electrodes. The strength of the current varies and the electric shock at time s may be uncomfortable. As the electric stimulation is for a brief duration there is no discomfort in between stimulations and will not last long. The response is recorded on the computer and can be observed on the computer screen. As there are several nerves in a limb, the procedure is repeated to test the different nerves.


The second part of the test is called Needle electromyography. A needle is stuck into different muscles and the response is recorded on the computer screen. The needles are thin and very fine. They are thinner than the needles used to draw blood. Usually 5-6 muscles are tested in each limb and at times other muscles in the body may be tested depending on the diagnosis. No electric shocks are delivered at time of the needle EMG test.

Results : The test results will be ready later that day and will be faxed or mailed to your primary care physician and the referring physician.
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Will gabapentin affect nerve conduction study?

Introduction – The most common type of neuropathy in adults is carpal tunnel syndrome (CTS) caused by compression of the median nerve at the wrist. The prevalence of CTS in the general population, in 2012, was near 3-3.8%, A higher prevalence was reported in women and in manual workers,

Some modalities such as conservative treatment, topical injections and surgery have been used for treatment of CTS, However, the efficacy of these treatments is limited and recurrence of symptoms is common, Current literature demonstrate a trend towards recommending early surgery for CTS cases with or without median nerve denervation, although the American Academy of Orthopedic Surgeons guideline recommends early surgical treatment only for cases with denervation,

CTS affects nerve conduction studies with entrapment of the median nerve. Some modalities like local corticosteroid injection and surgical decompression can significantly improve nerve conduction studies. Hui et al. suggested that surgical decompression resulted in greater improvement in median nerve conduction velocity than a single injection of steroid,

Gabapentin is an antiepileptic drug and structurally related to Gama-Amino Butyric Acid (GABA). Gabapentin action include high affinity binding to calcium channels and alteration of neurotransmitter release and blood serotonin levels, Gabapentin is used in a variety of neuropathic pain conditions such as diabetic neuropathy, post herpetic neuralgia, and spinal cord injury,

The safety and tolerability of this drug were reported by researchers, However, the studies on effects of gabapentin on nerve conduction studies have been limited. Gabapentin may close chloride channels and open calcium channels in neural cells, as well as change ion flow by membrane channels.

  1. Thus, these lead to decreased inhibitory post-synaptic potential and increased speed flow in neural cells.
  2. Taverner et al.
  3. Reported that after a 6-month followup of patients with CTS treated with 1800 mg/day of gabapentin, 5.3% and 26.3% patients showed improvement and normal electromyography findings, respectively,

This study aims to evaluate the efficacy of gabapentin on sensory nerve conduction velocity (SNCV) and distal motor latency (DML) in patients with mild CTS.
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What can throw off an EMG test?

About Electromyography – Electromyography measures the electrical impulses of the muscles at rest and when contracted. Electromyography is usually done with nerve conduction studies. Nerve conduction studies measure how well individual nerves transmit electrical signals to the muscles. Electromyography is done to:

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Diagnose diseases that damage muscle tissue, nerves or the points where nerve and muscle join. These disorders include a herniated disc, amyotrophic lateral sclerosis (ALS) or myasthenia gravis, Find out the cause of weakness, paralysis, involuntary muscle twitching or other symptoms. Problems in a muscle, the nerves controlling a muscle, the spinal cord or the brain can all cause these kinds of symptoms.

Electromyograms are useful in determining whether there has been pressure on a nerve or nerve root degeneration. The test involves placing small needles into the muscles. You may have mild discomfort from this. There are no major risks associated with this test. Tell your doctor if you:

Are taking any drugs. Certain drugs that act on the nervous system (such as muscle relaxants) can interfere with electromyography results. You may need to stop taking these three to six days before the test. Have had bleeding problems or are taking blood thinning drugs, such as warfarin (Coumadin®) or heparin. Have a pacemaker.

Do not smoke for at least three hours before the test. Wear loose-fitting clothing that permits access to the muscles and nerves to be tested. You may be given a hospital gown to wear. You will be asked to lie on a table or sit in a reclining chair so that the muscles being tested are relaxed and easy to reach.

Typically, the skin over the area being tested will be cleaned with an antiseptic. An electrode that combines a reference point and a needle for recording is inserted into the muscle. You will feel a brief, sharp pain when a needle electrode is inserted into the muscle. Some people find this uncomfortable.

The electrode is attached by wires to a recording machine. Once the electrodes are in place, the electrical activity in that muscle is recorded while the muscle is at rest. Then the technologist or doctor asks you to tense the muscle with gradually increasing force while the electrical activity in the muscle is recorded.

  1. The needle may be moved several times to record the electrical activity in different areas of the muscle or in different muscles.
  2. The electrical activity in the muscle shows as wavy and spiky lines on a special video monitor.
  3. It may also be heard on a loudspeaker as machine gun-like popping sounds when you contract the muscle.

The recording should show no electrical activity when the muscle is at rest. If the EMG shows electrical activity in a resting muscle, there may be a problem with the nerve supply to the muscle. This kind of activity can also be caused by inflammation or disease in the muscle.

Abnormal levels and duration of electrical discharges when a muscle contracts also suggest the presence of a muscle or nerve disorder, such as ALS, post-polio syndrome or a herniated disc. An EMG usually takes 30 to 60 minutes. Afterward, you may be given a pain reliever if you have any soreness. After EMG testing, you may feel a tingling sensation for a couple of days.

You may develop small bruises or swelling where the needle was inserted. The needles are sterilized, so there is little chance of developing an infection. If you do notice increasing pain, swelling, tenderness or pus at any of the needle insertion sites, call your doctor.
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Why was my nerve conduction study so painful?

How the Test will Feel – The impulse may feel like an electric shock. You may feel some discomfort depending on how strong the impulse is. You should feel no pain once the test is finished. Often, the nerve conduction test is followed by EMG. In this test, a needle is placed into a muscle and you are told to contract that muscle.
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What are 3 factors that may affect EMG signal?

Electrical noise and factors affecting EMG signal – The amplitude range of EMG signal is 0-10 mV (+5 to -5) prior to amplification. EMG signals acquire noise while traveling through different tissue. It is important to understand the characteristics of the electrical noise. Electrical noise, which will affect EMG signals, can be categorized into the following types:

  1. Inherent noise in electronics equipment : All electronics equipment generate noise. This noise cannot be eliminated; using high quality electronic components can only reduce it.
  2. Ambient noise: Electromagnetic radiation is the source of this kind of noise. The surfaces of our bodies are constantly inundated with electric-magnetic radiation and it is virtually impossible to avoid exposure to it on the surface of earth. The ambient noise may have amplitude that is one to three orders of magnitude greater than the EMG signal.
  3. Motion artifact: When motion artifact is introduced to the system, the information is skewed. Motion artifact causes irregularities in the data. There are two main sources for motion artifact: 1) electrode interface and 2) electrode cable. Motion artifact can be reduced by proper design of the electronics circuitry and set-up.
  4. Inherent instability of signal : The amplitude of EMG is random in nature. EMG signal is affected by the firing rate of the motor units, which, in most conditions, fire in the frequency region of 0 to 20 Hz. This kind of noise is considered as unwanted and the removal of the noise is important.

The factors that mainly affect the EMG signal can also be classified. This kind of classification is set so that EMG signal analysis algorithms can be optimized and equipments can be designed in a consistent manner. Factors affecting EMG signal falls into three basic categories:

  1. Causative Factors: This is the direct affect on signals. Causative factors can be divided into two classes:
    1. Extrinsic : This is due to electrode structure and placement. Factors like area of the detection surface, shape of electrode, distance between electrode detection surface, location of electrode with respect to the motor points in the muscle, location of the muscle electrode on the muscle surface with respect to the lateral edge of the muscle, orientation of the detection surfaces with respect to the muscle fibers mainly have an effect on EMG signal.
    2. Intrinsic : Physiological, anatomical, biochemical factors take place due to number of active motor units, fiber type composition, blood flow, fiber diameter, depth and location of active fibers and amount of tissue between surface of the muscle and the electrode.
  2. Intermediate Factors: Intermediate factors are physical and physiological phenomena influenced by one or more causative factors. Reasons behind this can be the band-pass filtering aspects of the electrode alone with its detection volume, superposition of action potentials in the detected EMG signal, conduction velocity of the action potential that propagate along the muscle fiber membrane. Even crosstalk from nearby muscle can cause Intermediate Factors.
  3. Deterministic Factors : These are influenced by Intermediate Factors. The number of active motor units, motor firing rate, and mechanical interaction between muscle fibers have a direct bearing on the information in the EMG signal and the recorded force. Amplitude, duration, and shape of the motor unit action potential can also be responsible.
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The maximization of the quality of EMG signal can be done by the following ways:

  1. The signal-to-noise ratio should contain the highest amount of information from EMG signal as possible and minimum amount of noise contamination.
  2. The distortion of EMG signal must be as minimal as possible with no unnecessary filtering and distortion of signal peaks and notch filters are not recommended.

During the EMG signal processing, only positive values are analyzed. When half-wave rectification is performed, all negative data is discarded and positive data is kept. The absolute value of each data point is used during full-wave rectification. Usually for rectification, full-wave rectification is preferred.
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Does magnesium affect nerve conduction?

Abstract – Divalent cations, such as calcium and magnesium, are constantly present in extracellular compartment of most organisms. Modification of extracellular concentrations of divalent ions causes changes in physiologic functions, such as excitability and conduction of the nerves.

  1. The present study was designed to investigate and compare the effects of calcium and magnesium on nerve conduction and lidocaine-induced nerve conduction block.
  2. The aim of our study was to contribute to better understanding of physiological and pharmacological roles of divalent cations.
  3. Experiments were conducted on the sciatic nerves by using the sucrose-gap recording technique.

We evaluated the effects of test solutions containing different calcium or magnesium concentrations, prepared with or without lidocaine, on compound action potentials to determine physiological and pharmacological roles of these cations. After the control recordings, the nerve was exposed to Ringer’s solution containing 0, 1.9, 3.8 mM Ca2+ and 1.9 and 3.8 mM Mg2+ with or without 1 mM lidocaine.

Decreasing the Ca2+ concentrations in Ringer’s solution with or without lidocaine enhanced both tonic and phasic blocks. However, increased Mg2+ concentration did not change the tonic blocks but increased the phasic blocks. In conclusion, the results suggested but not prove that Ca2+ and Mg2+ may have different mechanisms of action on peripheral nerves.

While Ca2+ directly affects the gating of Na+ channels, action of Mg2+ can be explained by surface charge theory.
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What improves nerve conduction speed?

Temperature – In general, the conduction velocities of most motor and sensory nerves are positively and linearly associated with body temperature (low temperatures slow nerve conduction velocity and higher temperatures increase conduction velocity). Conduction velocities in the Sural nerve seem to exhibit an especially strong correlation with the local temperature of the nerve.
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Can I drink caffeine before EMG?

Before the procedure: –

Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure. Generally, no fasting or sedation is required prior to the procedure. Notify your doctor of all medications (prescribed and over-the-counter) and herbal supplements that you are taking. Dress in clothes that permit access to the area to be tested or that are easily removed. Stop using lotions or oils on your skin for a few days before your procedure, or at least stop using them on the day of the exam. Based on your medical condition, your doctor may request other specific preparation.

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Can you eat and drink before a nerve conduction study?

∎ Please avoid using moisturising creams or gels on your skin on the day of the test as they can interfere with the test. ∎ Please remove any jewellery or watches before the test (a wedding band is fine). ∎ You can eat, drink and take any medicine as usual. ∎ Please bring a list of medicines you may be on.
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Why was my EMG so painful?

The Pain of an EMG – Pain is the most common complication of EMG 2 causing some level of discomfort in all patients either from the nerve conduction portion or the needle examination. Most surveys find pain more common in the needle portion.3 The study is typically well tolerated but for some patients it is nearly unbearable.

It is crucial to discuss and understand a patient’s pain before referring to EMG because stopping midstudy because of pain sacrifices patients’ resources, adds to their discomfort, and creates the challenge of interpretation from limited data for the electromyographer. Patients who report higher pretest pain and anxiety typically report more pain during the procedure.4 There have been attempts to alleviate pain during EMG with pharmacologic interventions (eg, skin sprays or oral analgesics) and with nonpharmacologic interventions (eg, calming music and/or providing preprocedure information about the test to alleviate anxiety).5 Patients have varied levels of understanding and perceptions of EMG.

In a study of new patients at an EMG lab, 52.1% of patients had either no information or incorrect information about EMG, and only 28.2% were considered informed.6 Giving information before the test may be helpful. Some studies have found women having nerve conduction studies perceived less pain when they were given informational handouts prior to the study, although this did not apply to the needle portion of the exam and the effect was not seen in men.

Women have more pain during EMG or at least acknowledge and report it.3 Accurate muscle selection is an important and modifiable aspect of the pain caused by EMG, making it crucial that electromyographers perform accurate muscle selection.7 Although the procedure may induce pain, it is important to note that it is not a severely painful experience for most patients.

A study found that 82% of patients said the test was “not as bad as they expected,” and most patients noted only mild pain.8 It is important that referrals include clear descriptions of symptoms and a thoughtful diagnostic question for the electromyographer to evaluate (Box). Alternatives to Needle EMG Electrodiagnostic tests that are painless may also be considered for diagnosing neuromuscular diseases including surface EMG (sEMG), which can complement a nerve conduction study and/or needle examination. Muscle signals are examined with surface electrodes in sEMG rather than through the traditional needle electrode.

Currently, sEMG is mostly used to evaluate nonneurologic diagnoses. An evidence-based review from the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) suggests there is class C evidence that sEMG may be helpful in diagnosing neuromuscular diseases; it is rarely used for this purpose, and that is likely to remain so until further studies are done.10 A more frequently used “pain-free” electrodiagnostic test is neuromuscular ultrasound, which is used to diagnose neuropathies and focal deficits and monitor muscle health.

Neuromuscular ultrasound is accurate for diagnosis of median neuropathy at the wrist, and level A evidence suggests it may be offered for this diagnosis.11 For patients in pain caused by median neuropathies, or for example from wrist arthritis leading to the compression, an accurate pain-free study may be quite helpful.
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What should you not take before an EMG?

Do not take any Excedrin (which contains Aspirin), over-the-counter anti-inflammatory medications (such as Advil, Aleve, Aspirin, etc.), or prescription NSAID’s (naproxen, motrin, etc.) for at least 5 days prior to the procedure.
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Does MS show up on nerve conduction study?

Visual evoked potential test – This test screens for damage to the optic nerve and is considered the most common nerve conduction study used in an MS diagnosis. The technologist places electrodes on key areas of your face and scalp, then sits you in front of a monitor to stare at a bizarre checkerboard test pattern that moves while they test each eye separately.
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Can anxiety affect EMG results?

Abstract – Experience of stress may lead to increased electromyography (EMG) activity in specific muscles compared to a non-stressful situation. The main aim of this study was to develop and validate a stress-EMG paradigm in which a single uncontrollable and unpredictable nociceptive stimulus was presented.

EMG activity of the trapezius muscles was the response of interest. In addition to linear time effects, non-linear EMG time courses were also examined. Taking into account the hierarchical structure of the dataset, a multilevel random regression model was applied. The stress paradigm, executed in N = 70 subjects, consisted of a 3-minute baseline measurement, a 3-minute pre-stimulus stress period and a 2-minute post-stimulus phase.

Subjects were unaware of the precise moment of stimulus delivery and its intensity level. EMG activity during the entire experiment was conform a priori expectations: the pre-stimulus phase showed a significantly higher mean EMG activity level compared to the other two phases, and an immediate EMG response to the stimulus was demonstrated.

In addition, the analyses revealed significant non-linear EMG time courses in all three phases. Linear and quadratic EMG time courses were significantly modified by subjective anticipatory stress level, measured just before the start of the stress task. Linking subjective anticipatory stress to EMG stress reactivity revealed that subjects with a high anticipatory stress level responded with more EMG activity during the pre-stimulus stress phase, whereas subjects with a low stress level showed an inverse effect.

Results suggest that the stress paradigm presented here is a valid test to quantify individual differences in stress susceptibility. Further studies with this paradigm are required to demonstrate its potential use in mechanistic clinical studies.
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Can a fatigued muscle still produce an EMG?

Abstract – Muscle fatigue can be identified by a decrease in the frequency components of the EMG signal, typically represented by a fall in the center frequency (fc). In addition, changes in muscle length have been demonstrated to independently alter the EMG fc.

What remains unknown is the interaction between muscle fatigue and muscle length changes on the EMG fc. To address this question, a human biceps model of muscle fatigue, consisting of repetitive non-isometric contractions until task failure was studied. EMG signals from the biceps brachii were acquired via surface electrodes, and muscle length was determined by recording elbow angle.

Five subjects developed biceps fatigue by repeating contractions of 50% maximal force until task failure. Fatigue produced a decrease in EMG fc at all muscle lengths. For the first three quarters of fatigue development there was a similar degree of reduction in EMG fc at all muscle lengths.

But as task failure approached, there was a greater reduction in EMG fc at the shortest muscle length relative to the longest muscle length (41% reduction from baseline versus 30% reduction from baseline, respectively). The effect of muscle length independent of fatigue was such that a 20% increase in length would result in approximately an 18% fall in EMG fc.

In conclusion, during fatigue development muscle length significantly influences the EMG fc, and it may be an important factor to consider when utilizing the EMG fc to detect muscle fatigue.
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Is a nerve conduction test worth it?

What are they used for? – EMG and nerve conduction studies are used to help diagnose a variety of muscle and nerve disorders. An EMG test helps find out if muscles are responding the right way to nerve signals. Nerve conduction studies help diagnose nerve damage or disease.
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Is nerve conduction test harmful?

1. Basic considerations – It is widely recognized in the literature that electrodiagnostic studies are generally well tolerated ( Dumitru et al., 2002, Preston and Shapiro, 2013,). On the other hand transient mild procedural pain and discomfort are very common, and in fact the most frequent “undesired effect” that patients will experience. The discomfort, or mild pain experienced by some patients, following the application of electrical stimulation during nerve conduction studies (NCS) is transient and self-limiting and will not initiate or aggravate pre-existing symptoms beyond the duration of the actual investigation. Adverse events such as self-limiting mild tenderness and/or bruising commonly follow an ‘uncomplicated’ needle electromyography (EMG) examination. Some patients might be unable to cooperate with or even tolerate supramaximal electrical stimulation or needle examination, especially when patients have been sensitized previously. In the context of consent patients need to be advised that this might limit the diagnostic yield and sensitivity of the investigation, but could be informed about potential alternative diagnostic tests (e.g. Magnetic Resonance Imaging in the investigation of radiculopathy). We recommend documenting this in the final report. Presyncope and even syncope are well known to Electromyographers, albeit relatively uncommon (<1/100). View complete answer

What improves nerve conduction speed?

Temperature – In general, the conduction velocities of most motor and sensory nerves are positively and linearly associated with body temperature (low temperatures slow nerve conduction velocity and higher temperatures increase conduction velocity). Conduction velocities in the Sural nerve seem to exhibit an especially strong correlation with the local temperature of the nerve.
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