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Nerve conduction studies: essentials and pitfalls in practice
  1. A Mallik,
  2. A I Weir
  1. Department of Clinical Neurophysiology, Institute of Neurological Sciences, Southern General Hospital, Glasgow, UK
  1. Correspondence to:
 Dr Arup Mallik
 Department of Clinical Neurophysiology, Institute of Neurological Sciences, Southern General Hospital, Glasgow G51 4TF, UK;

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A neurologist has sent a patient for nerve conduction studies (NCS) and has received the report, but what does it mean? We hope to remove some of the mysteries that may surround NCS. The techniques and how they are affected by disease are described in general terms. These principles can be applied to specific conditions discussed elsewhere. We also discuss the numerous pitfalls that may be encountered with NCS. Understanding these basic concepts will allow you to get the most from your clinical neurophysiology department.

NCS are only part of a complete peripheral neurophysiological examination (PNE) and are frequently accompanied by a needle electromyogram (EMG). The combination of both techniques and those detailed in other articles in this issue are often required for a complete diagnostic study. The process of choosing the appropriate tests is the responsibility of the clinical neurophysiologist (CN) and not the referring doctor and is planned as a dynamic series of steps designed to answer specific questions about nervous system function raised by the clinical picture.


Clinical neurophysiologists can employ a confusing number of terms and abbreviations. Box 1 lists the ones we use frequently.

Box 1: List of abbreviations and terminology used

  • ACh: acetylcholine

  • AIDP: acute inflammatory demyelinating polyneuropathy

  • AMAN: acute motor axonal neuropathy

  • CMAP: compound muscle action potential

  • CN: clinical neurophysiologist

  • DRG: dorsal root ganglion

  • EMG: electromyogram

  • LEMS: Lambert-Eaton myasthenic syndrome

  • MG: myasthenia gravis

  • NAP: nerve action potential

  • NCS: nerve conduction studies

  • NMTD: neuromuscular transmission disorders

  • PNE: peripheral neurophysiological examination

  • PNS: peripheral nervous system

  • RNS: repetitive nerve stimulation

  • SNAP: sensory nerve action potential

  • TMS: transcranial magnetic stimulation

  • Conduction block: A reduction of proximal CMAP area/amplitude of at least 20% (usually > 50%) compared with distal CMAP area/amplitude. The duration of the proximal CMAP should not increase by > 20% (see temporal dispersion)

  • Temporal dispersion: …

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