What Medications Affect Nerve Conduction Study?

A nerve conduction study (NCS) is a medical test that measures the function and speed of electrical signals in the nerves. It can help diagnose various nerve disorders, such as carpal tunnel syndrome, peripheral neuropathy, and Guillain-Barré syndrome. NCS involves stimulating a nerve with a small electric shock and recording the response from a muscle or a sensory receptor. The response is measured by parameters such as amplitude, latency, and conduction velocity.

NCS is usually performed along with needle electromyography (EMG), which measures the electrical activity of muscles at rest and during contraction. EMG can provide additional information about the location and severity of nerve or muscle damage.

NCS and EMG are generally safe and well-tolerated procedures, but some factors can affect their accuracy and reliability. One of these factors is medication use. Some medications can interfere with nerve or muscle function and alter the results of NCS and EMG. Therefore, it is important to inform your doctor about any medications you are taking before undergoing these tests.

Medications that can affect NCS and EMG

The following is a list of some common medications that can affect NCS and EMG, along with their possible effects and recommendations:

Anticholinesterase drugs: These drugs inhibit the enzyme that breaks down acetylcholine, a neurotransmitter that stimulates muscle contraction. Examples include pyridostigmine, neostigmine, edrophonium, and donepezil. These drugs can increase the amplitude and duration of the compound muscle action potential (CMAP), which is the response recorded from a muscle during NCS. They can also reduce the decremental response seen in myasthenia gravis, a condition that causes muscle weakness due to impaired neuromuscular transmission. Therefore, these drugs should be discontinued at least 12 hours before NCS and EMG, unless otherwise instructed by your doctor.

Aminoglycoside antibiotics: These drugs are used to treat serious bacterial infections. Examples include gentamicin, amikacin, tobramycin, and streptomycin. These drugs can block the neuromuscular junction and cause muscle weakness or paralysis. They can also reduce the amplitude of the CMAP and the sensory nerve action potential (SNAP), which is the response recorded from a sensory receptor during NCS. Therefore, these drugs should be avoided or used with caution before NCS and EMG, especially in patients with pre-existing neuromuscular disorders.

Lithium: This drug is used to treat bipolar disorder and other mood disorders. It can affect nerve conduction velocity (NCV), which is the speed of electrical signals in the nerves. Lithium can cause either slowing or speeding of the NCV, depending on the dose and duration of use. Therefore, lithium levels should be monitored before NCS and EMG, and the results should be interpreted with caution.

Phenytoin: This drug is used to treat epilepsy and other seizure disorders. It can affect the NCV by causing either slowing or speeding, depending on the dose and duration of use. It can also reduce the amplitude of the CMAP and SNAP. Therefore, phenytoin levels should be monitored before NCS and EMG, and the results should be interpreted with caution.

Statins: These drugs are used to lower cholesterol levels and prevent cardiovascular diseases. Examples include atorvastatin, simvastatin, rosuvastatin, and pravastatin. These drugs can cause muscle damage or inflammation (myopathy or myositis), which can affect the EMG results by showing abnormal spontaneous activity or reduced recruitment of muscle fibers during contraction. Therefore, statins should be discontinued if there are signs or symptoms of muscle toxicity before NCS and EMG.

Corticosteroids: These drugs are used to treat various inflammatory conditions, such as asthma, rheumatoid arthritis, lupus, and multiple sclerosis. Examples include prednisone, methylprednisolone, dexamethasone, and hydrocortisone. These drugs can affect the EMG results by causing false-negative findings in patients with myopathy or myositis due to their anti-inflammatory effects. They can also cause false-positive findings in patients with neuropathy due to their immunosuppressive effects. Therefore, corticosteroids should be used with caution before NCS and EMG, and their dosage should be adjusted according to the clinical condition.

Indications for Nerve Conduction Study:

1. Evaluation of peripheral nerve disorders such as carpal tunnel syndrome, neuropathy, or radiculopathy.
2. Assessment of nerve injuries or compression.
3. Diagnosis of neuromuscular disorders like myasthenia gravis or muscular dystrophy.
4. Monitoring disease progression or treatment efficacy in conditions like diabetic neuropathy.
5. Identification of nerve involvement in conditions such as Guillain-Barré syndrome or multiple sclerosis.
6. Pre-operative assessment for nerve-related surgeries.

Contraindications for Nerve Conduction Study:

1. Active skin infection or open wounds at the electrode placement sites.
2. Allergy or sensitivity to the electrode gel or other materials used during the study.
3. Presence of a cardiac pacemaker or implantable defibrillator in the area being tested (specific to certain nerve conduction study techniques).
4. Uncontrolled bleeding disorder or anticoagulant use in some cases (precautions may be taken).

CPT Code for Nerve Conduction Study:

The CPT code commonly used for Nerve Conduction Studies is 95900 (Nerve conduction studies; 1-2 studies). However, specific circumstances and requirements may warrant the use of different codes such as 95903 (Nerve conduction studies; 3-4 studies) or other relevant codes. It is important to consult with the healthcare provider or medical coding specialist for accurate coding based on the specific clinical scenario and requirements.

Conclusion

NCS and EMG are useful tests to evaluate the function of the nerves and muscles, but they can be affected by various medications that can alter the electrical signals or the neuromuscular transmission. Therefore, it is important to inform your doctor about any medications you are taking before undergoing these tests and follow their instructions regarding discontinuation or adjustment of the dosage. This can help ensure the accuracy and reliability of the test results and avoid potential complications.

References

(1) Nerve conduction study – Wikipedia.
(2) Nerve conduction studies: Basic concepts – PubMed.

FAQs

What are NCS and EMG?

NCS and EMG are medical tests that measure the function and speed of electrical signals in the nerves and muscles. They can help diagnose various nerve and muscle disorders, such as carpal tunnel syndrome, peripheral neuropathy, and myasthenia gravis.

How are NCS and EMG performed?

NCS involves stimulating a nerve with a small electric shock and recording the response from a muscle or a sensory receptor. EMG involves inserting a thin needle electrode into a muscle and recording the electrical activity at rest and during contraction. Both tests are usually done by a neurologist or a physiatrist who specializes in electrodiagnostic medicine.

Are NCS and EMG painful?

NCS may cause a mild tingling or twitching sensation when the nerve is stimulated. EMG may cause some discomfort or pain when the needle is inserted into the muscle. However, both tests are generally well-tolerated and last for about 30 to 60 minutes.

What are the risks or complications of NCS and EMG?

NCS and EMG are generally safe and have minimal risks or complications. However, some possible side effects include:

• Bruising, bleeding, or infection at the needle insertion site
• Allergic reaction to the electrode gel or tape
• Muscle soreness or cramps after the test
• Aggravation of existing nerve or muscle symptoms
• Interference with implanted electrical devices, such as pacemakers or defibrillators

How should I prepare for NCS and EMG?

Before undergoing NCS and EMG, you should:

• Inform your doctor about any medications you are taking, especially those that can affect nerve or muscle function, such as anticholinesterase drugs, aminoglycoside antibiotics, lithium, phenytoin, statins, or corticosteroids. You may need to stop or adjust the dosage of some medications before the test.
• Inform your doctor about any medical conditions you have, especially those that can affect nerve or muscle function, such as diabetes, kidney disease, thyroid disease, blood disorders, infections, or neuromuscular disorders. You may need to have some blood tests or other investigations before the test.
• Inform your doctor if you have any implanted electrical devices, such as pacemakers or defibrillators. You may need to have them turned off or adjusted before the test.
• Avoid using any creams, lotions, oils, or powders on your skin before the test. They can interfere with the electrical signals or the electrode attachment.
• Wear loose-fitting and comfortable clothing that allows easy access to the areas to be tested. You may need to remove some clothing or jewelry during the test.
• Avoid smoking, drinking caffeine, or exercising for at least three hours before the test. They can affect nerve or muscle function.

How should I care for myself after NCS and EMG?

After undergoing NCS and EMG, you should:

• Apply ice packs or take over-the-counter pain relievers if you have any bruising, bleeding, soreness, or cramps at the needle insertion site. Avoid rubbing or scratching the area.
• Keep the needle insertion site clean and dry. Cover it with a bandage if needed. Watch for any signs of infection, such as redness, swelling, warmth, pus, or fever. Contact your doctor if you notice any of these signs.
• Resume your normal activities and medications as instructed by your doctor. Avoid any strenuous activities that may aggravate your nerve or muscle symptoms for at least 24 hours after the test.
• Follow up with your doctor to discuss the results of the test and the next steps in your treatment plan.

Q: Which medications can affect nerve conduction study results?

A: Certain medications such as muscle relaxants, anti-seizure drugs, and certain antidepressants can potentially impact nerve conduction study outcomes.

Q: Do specific medications interfere with the accuracy of nerve conduction studies?

A: Yes, some medications can interfere with nerve conduction study accuracy by affecting nerve signals or muscle responses.

Q: What prescription drugs should be avoided before a nerve conduction study?

A: It is recommended to inform your healthcare provider about all prescription medications you are taking before a nerve conduction study to ensure accurate results.

Q: Can over-the-counter medications influence the results of a nerve conduction study?

A: Some over-the-counter medications, particularly those that affect muscle relaxation or nerve function, can potentially impact nerve conduction study outcomes.

Q: What should I discuss with my healthcare provider regarding medications before a nerve conduction study?

A: It is important to inform your healthcare provider about all medications you are taking, including prescription drugs, over-the-counter medications, and supplements, to assess their potential impact on the study.

Q: How long should I stop taking certain medications before a nerve conduction study?

A: The duration for stopping specific medications before a nerve conduction study varies. Your healthcare provider will provide instructions based on the medications you are taking.

Q: Are there alternative testing options if I’m taking medications that affect nerve conduction study?

A: In some cases, alternative testing options or adjustments may be available if certain medications interfere with nerve conduction study results. Consult with your healthcare provider to explore suitable alternatives.

Q: What are the potential effects of medication interference on nerve conduction study interpretation?

A: Medications that influence nerve conduction study results can potentially affect the accuracy of the test, leading to misinterpretation of nerve function or muscle responses.

Q: Should I inform my doctor about all medications, including supplements, before a nerve conduction study?

A: Yes, it is crucial to inform your doctor about all medications and supplements you are taking as they can potentially impact the nerve conduction study results.

Q: How can I ensure accurate nerve conduction study results when considering medications?

A: To ensure accurate results, it is recommended to have a thorough discussion with your healthcare provider about all medications, including prescription drugs, over-the-counter medications, and supplements, prior to the nerve conduction study.