2026 Workshop Handout Bundle-W123B - Basic NCS

W123B - Basic NCS - Hayat

Pdf Summary

Nerve conduction studies (NCSs), usually performed alongside electromyography, help evaluate focal and generalized neuropathies and distinguish peripheral nerve disorders from conditions such as radiculopathy or motor neuron disease. Routine NCSs assess large, fast-conducting fibers; suspected small-fiber neuropathy may require skin biopsy.<br /><br />In an NCS, a peripheral nerve is electrically stimulated and the resulting response is recorded from a muscle or sensory nerve. Reliable results depend on correct electrode placement, adequate supramaximal stimulation, accurate distance measurement, appropriate instrument settings, stable electrodes, and warmed limbs. Motor studies commonly assess median, ulnar, tibial, and peroneal nerves; sensory studies record sensory nerve action potentials (SNAPs).<br /><br />Key measurements include response amplitude, duration, area, and latency. Motor conduction velocity is calculated from the distance between stimulation sites divided by the difference in their latencies. F-waves provide information about more proximal nerve segments. Sensory response amplitude and morphology vary with electrode type, stimulation direction, distance, and skin temperature.<br /><br />Interpretation must account for age, height, sex, nerve segment, and especially temperature. Common technical errors include stimulus spread, inadequate stimulation, inaccurate distance measurements, poor recording-electrode placement, shock artifact, unstable electrodes, and anomalous nerve connections. Ultrasound guidance can improve stimulation of certain deep or difficult-to-localize nerves and may reduce discomfort.<br /><br />NCS patterns help characterize disorders. Focal compression often prolongs distal latencies; demyelinating neuropathy slows conduction, while axonal neuropathy chiefly reduces response amplitudes. Absent or delayed F-waves may suggest acute polyradiculopathy. A missing SNAP, after technical causes are excluded, can indicate sensory neuronopathy. However, normal NCS results do not rule out early neuropathy, small-fiber or autonomic neuropathy, radiculopathy, neuromuscular-junction disorders, or myopathy.

Keywords

nerve conduction studies

ncs

electromyography

EMG

peripheral neuropathy

radiculopathy

motor neuron disease

MND

small-fiber neuropathy

sensory nerve action potentials

F-waves

demyelinating neuropathy

axonal neuropathy