Electrodiagnostic Criteria (EFNS/PNS)

Carol L. Koski, M.D. and Richard A. Lewis, M.D., Principal Authors

Information adapted from Joint Task Force of the EFNS and the PNS, 2005

1. Definite

At least one of the following:

1. At least 50% prolongation of motor distal latency above the upper limit of normal values in two nerves, or
2. At least 30% reduction of motor conduction velocity below the lower limit of normal values in two nerves, or
3. At least 20% prolongation of F-wave latency above the upper limit of normal values in two nerves (>50% if amplitude of distal negative peak CMAP, 80% of lower limit of normal values), or v
4. Absence of F-waves in two nerves if these nerves have amplitudes of distal negative peak CMAPs at least 20% of lower limit of normal values + at least one other demyelinating parameter* in at least one other nerve, or
5. Partial motor conduction block: at least 50% amplitude reduction of the proximal negative peak CMAP relative to distal, if distal negative peak CMAP at least 20% of lower limit of normal values, in two nerves, or in one nerve + at least one other demyelinating parameter* in at least one other nerve, or
6. Abnormal temporal dispersion (>30% duration increase between the proximal and distal negative peak CMAP) in at least two nerves, or
7. Distal CMAP duration (interval between onset of the first negative peak and return to baseline of the last negative peak) of at least 9 ms in at least one nerve + at least one other demyelinating parameter* in at least one other nerve

2. Probable

At least 30% amplitude reduction of the proximal negative peak CMAP relative to distal, excluding posterior tibial nerve, if distal negative peak CMAP at least 20% of lower limit of normal values, in two nerves, or in one nerve + at least one other demyelinating parameter* in at least one other nerve

3. Possible

As in (1) but in only one nerve

CMAP, compound muscle action potential. To apply these criteria, the median, ulnar (stimulated below the elbow), peroneal (stimulated below the fibular head), and tibial nerves on one side are tested. Temperatures should be maintained at least 33° C at the palm and 30° C at the external malleolus (good practice points).

* Any nerve meeting any of the criteria (a-g).