Nerve conduction studies and EMG: axonal loss versus demyelination
What CMAP and SNAP amplitude, latency, conduction velocity, F waves and repetitive stimulation measure, how they separate axonal loss from demyelination and pre- from postganglionic lesions, and how needle EMG distinguishes neurogenic from myopathic disease.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Nerve conduction studies (NCS) stimulate a nerve and record a compound muscle action potential (CMAP) from muscle or a sensory nerve action potential (SNAP) from the nerve.
- Amplitude counts working axons. Latency and velocity measure the speed of the fastest myelinated fibres.
- Axonal loss lowers amplitude. Demyelination slows conduction and causes conduction block.
Loading the rest of the note…
Finished reading?
Sources
- Principles of Neural Science (6th ed.)McGraw Hill (Kandel, Koester, Mack and Siegelbaum, 2021), 2021
- Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic-Ultrasound Correlations (4th ed.)Elsevier (Preston and Shapiro, 2020), 2020
- Van den Bergh PYK et al. European Academy of Neurology/Peripheral Nerve Society guideline on diagnosis and treatment of chronic inflammatory demyelinating polyradiculoneuropathy: report of a joint task force, second revision. Eur J Neurol 2021;28:3556-83European Journal of Neurology, 2021
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Turnstile bot check on sign-in and signed-out feedback