What is the role of electromyography (EMG) in the diagnosis of peroneal mononeuropathy?

Updated: Jun 08, 2018
  • Author: Shaheen E Lakhan, MD, PhD, MS, MEd; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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EMG is useful to localize the lesion. It can be helpful in determining which nerve is involved primarily—the common peroneal nerve at the knee or one of its two branches, the superficial or deep peroneal nerve. The tibialis anterior or extensor hallucis longus muscles (ie, innervated by the deep peroneal) and the peroneus longus or brevis muscles (ie, innervated by the superficial peroneal) are useful to study for this purpose.

EMG also is helpful in determining if the foot drop is due to an L5 radiculopathy or a sciatic lesion. In an L5 radiculopathy, the tibialis posterior, which is a foot inverter, and the lumbosacral paraspinous muscles are involved.

Involvement of the peroneal division of the sciatic nerve in the thigh or hip area is more difficult to determine clinically. In the thigh, the peroneal division of the sciatic nerve innervates the short head of the biceps femoris muscle, a knee flexor. As isolating this muscle clinically is difficult, EMG may be necessary to determine involvement.

If lesions in the thigh are suspected on EMG, then MRI of the thigh (evaluating for cysts or tumors) is indicated.

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