Do you order electromyography (EMG) and nerve‑conduction studies (NCS) together?

Should EMG and NCS Be Ordered Together?

Yes, EMG and nerve conduction studies (NCS) should be performed together in the same session, except in rare unique situations, as ordering NCS alone provides incomplete diagnostic information and can lead to missed diagnoses. 1

Why Combined Testing Is Essential

The American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) takes a firm position that NCS and needle EMG must be performed together because:

• NCS alone captures only part of the diagnostic picture and cannot adequately evaluate muscle, nerve root, or most nerve disorders 1
• Common diagnoses require needle EMG data combined with NCS data to reach accurate conclusions 1
• Needle EMG is necessary for diagnosing myopathy, radiculopathy, plexopathy, motor neuron disorders, peripheral neuropathies, and most individual peripheral motor nerve disorders 1
• Relying solely on NCS data is often misleading and results in important diagnoses being missed, potentially subjecting patients to incorrect or harmful treatment 1

Clinical Context Where This Matters Most

Conditions Requiring Combined Testing

For peripheral neuropathy evaluation:

• NCS shows diffuse abnormalities with relatively uniform involvement across tested nerves in polyneuropathy 2
• EMG reveals length-dependent patterns of abnormalities that confirm the diagnosis 3
• Combined testing differentiates between axonal versus demyelinating processes 4

For ICU-acquired weakness:

• Both EMG (used in 90% of studies) and NCS (used in 84% of studies) are standard diagnostic tools 2
• The positive predictive value of EMG alone for weakness diagnosis is only 50%, with negative predictive value of 89% 2

For radiculopathy:

• NCS may be completely normal in nerve root compression 5
• Needle EMG is essential to detect denervation patterns that confirm the diagnosis 5

The Rare Exceptions

When NCS alone may be sufficient:

• Classic distal symmetric diabetic neuropathy with stocking-glove distribution, reduced ankle reflexes, and known risk factors can be diagnosed clinically without any electrodiagnostic testing 3
• Carpal tunnel syndrome or other focal entrapment neuropathies where the clinical diagnosis is straightforward 4

Common Pitfalls to Avoid

Ordering NCS without EMG:

• This practice increases healthcare costs while providing inadequate diagnostic information 1
• It leads to incomplete evaluation that may miss myopathies, radiculopathies, and motor neuron diseases 1

Using electrodiagnostic studies for routine monitoring:

• For stable peripheral neuropathy (such as in polyarteritis nodosa), serial neurologic examinations are preferred over repeated EMG/NCS every 6 months 2
• Repeated EMG in patients with stable symptoms is not recommended due to its invasive nature 2
• Repeat testing is only warranted when there is uncertainty about new or worsening neurological processes 2, 3

Performing studies too early:

• Studies done within the first week of symptom onset may be normal in 30-34% of patients with active demyelinating disease 3
• Repeat testing 2-3 weeks later is essential when initial studies are normal but clinical suspicion remains high 3

Practical Implementation

The electrodiagnostic consultation should:

• Be performed by a physician with comprehensive knowledge of neuromuscular disorders who directly supervises and interprets both NCS and EMG 1
• Include a focused history and physical examination by the interpreting physician 1
• Use a study design determined by the trained neuromuscular physician based on clinical findings 1
• Integrate needle EMG findings with NCS data rather than reviewing NCS data in isolation 1

The combined study provides:

• Quantification of nerve conduction velocity and amplitude of sensory and motor potentials from NCS 4
• Detection of myopathic changes and signs of denervation from needle EMG 4
• Determination of whether damage is axonal or demyelinating, and whether distribution is generalized, multifocal, or focal 4