What NCS and EMG measure
Nerve conduction studies assess how efficiently electrical signals travel along peripheral nerves. Surface electrodes deliver small electrical impulses and record the response at a distance from the stimulation site. Key measurements include nerve conduction velocity, amplitude and distal latency. Slowed conduction with reduced amplitude suggests axonal loss; markedly slowed conduction with preserved amplitude suggests demyelination.
Electromyography (EMG) involves a thin needle electrode inserted into muscle to record electrical activity at rest and during voluntary contraction. Abnormal spontaneous activity (fibrillations, positive sharp waves) indicates active denervation; reduced recruitment patterns suggest motor unit loss. Together, NCS and EMG localise the lesion, quantify severity, distinguish axonal from demyelinating pathology, and guide prognosis and treatment planning.
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What to expect during the test
NCS produces a brief, sharp sensation during each electrical impulse — similar to a static electricity shock. The intensity is adjustable and most patients tolerate it well. EMG needle insertion causes brief discomfort; some patients experience mild soreness for a day afterward. The study typically takes 30–60 minutes depending on the number of nerves and muscles tested.
No special preparation is usually required. Patients should inform the clinician of any anticoagulant medications, bleeding disorders or pacemaker presence. Bringing a list of current medications and prior test results helps contextualise findings. The clinician interprets results alongside clinical history and examination — NCS/EMG findings are not interpreted in isolation.
When NCS/EMG is ordered
NCS/EMG is ordered when clinical evaluation suggests a specific nerve or muscle condition and the results would change management. Common indications include suspected peripheral neuropathy (diabetic, nutritional, autoimmune), carpal tunnel syndrome or other entrapment neuropathies, radiculopathy, motor neuron disease, neuromuscular junction disorders (myasthenia gravis, Lambert-Eaton), and myopathy.
The tests are not ordered as screening tools for vague symptoms. Results are most informative when symptoms have been present for at least 2–3 weeks (allowing denervation changes to appear on EMG) and when clinical findings already suggest a specific localisation. Dr. Jitendra Prasad Yadav (NMC 8029) discusses the rationale for testing at Kathmandu Neurology Clinic & Cognitive Center, Durbar Marg, Opposite of Yak & Yeti Hotel, ensuring patients understand what the tests can and cannot show.
- Peripheral neuropathy — axonal vs demyelinating classification
- Entrapment neuropathies — carpal tunnel, ulnar neuropathy
- Radiculopathy — root-level denervation patterns
- Motor neuron disease — fasciculations, denervation
- Neuromuscular junction — repetitive nerve stimulation
- Myopathy — brief, early recruitment, myopathic potentials