Which electrodiagnostic studies are indicated in the evaluation of tarsal tunnel syndrome?

Updated: Oct 15, 2019
  • Author: Minoo Hadjari Hollis, MD; Chief Editor: Thomas M DeBerardino, MD  more...
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Kaplan and Kernahan reported that reduced amplitude and increased duration of the motor response are more sensitive indicators of tarsal tunnel syndrome than distal motor latency is. [41] Sensory action potentials may be affected in earlier stages than motor fibers are; therefore, changes may also be identified before any motor abnormalities. This is because sensory fibers are more susceptible to injury.

In addition, Kaplan and Kernahan believed that the lateral plantar branch of the posterior tibial nerve probably is affected earlier than the nerve’s medial plantar branch is. Sensory studies are, therefore, considered to be the most sensitive studies for tibial nerve entrapment.

Galardi et al reported that after stimulation of the plantar nerves, the accuracy of the sensory-nerve action potential (SNAP) and the mixed-nerve action potential (MNAP) are almost the same. SNAPs are more sensitive and less specific, whereas MNAPs are less sensitive and more specific. Galardi et al concluded that the coexistence of MNAP and SNAP abnormalities, especially if asymmetric, is highly indicative of tarsal tunnel syndrome. The mixed-response test is technically much easier to perform and is better tolerated by many patients.

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