Nerve conduction · Advanced
Conduction block and temporal dispersion
Conduction block & temporal dispersion
Compare amplitude, area and duration when assessing proximal and distal responses.
01Two distinct concepts
- Conduction block means some motor axons fail to conduct across a segment.
- Temporal dispersion reflects increased differences in conduction time. The CMAP broadens and phase cancellation can lower amplitude.
02Exclude confounders
- Confirm proximal supramaximal stimulation, stable electrodes, distance, co-stimulation and anatomical communications.
- Not every proximal amplitude drop is pathological block. Proximal tibial responses need particular care.
03Apply the appropriate criteria
- Choose criteria for the disease, nerve, segment and distal CMAP size.
- Retain waveforms and measurements, documenting dispersion and interpretive limitations.
Related nerves
Pause and explain
Explain in your own words: “Block is a physiological inference, not a diagnosis from one amplitude percentage.” Then think of a situation in which it could be misinterpreted.
Show a review prompt
Do not mix criteria for CIDP, MMN and focal entrapment neuropathies.
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References and further reading
- EAN/PNS guideline on diagnosis and treatment of CIDP, second revision (2021) ↗EAN / PNS · Clinical guideline · Link accessed 2026-09-08
- Pitfalls in Using Electrophysiological Studies to Diagnose Neuromuscular Disorders (2012) ↗Journal of Clinical Neurology · Peer-reviewed review · Link accessed 2026-09-08
- Mid-palm recording technique, a new electrodiagnostic approach in Martin–Gruber anastomosis (2020) ↗Clinical Neurophysiology Practice · Original case research · Link accessed 2026-09-08
Educational synthesis; independent neuromuscular specialist review is pending. Publication dates and compilation dates are distinct. This is an original teaching synthesis; consult the source for complete methods and criteria.