Peroneal Mononeuropathy Workup

Updated: May 22, 2017
  • Author: Shaheen E Lakhan, MD, PhD, MS, MEd; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Workup

Imaging Studies

The following imaging studies are useful in peroneal mononeuropathy. [24]

  • MRI of the lower thigh or popliteal fossa may be indicated if a mass lesion is suspected. Peripheral nerve nodular mass lesions and inflammatory pseudotumors of the peripheral nerves may be detected and confirmed by pathological excision. [25]
  • MRI can also detect variations in the posterior and distal extents of the biceps femoris muscle, which can produce a tunnel in which the common peroneal nerve travels causing peroneal nerve compression. [26]
  • Color duplex ultrasonography and angiography can reveal a popliteal artery pseudoaneurysm in the popliteal fossa. [27]
  • High resolution sonography of the common peroneal nerve may identify structural lesions of the peroneal nerve such as intraneural ganglion [28] and inflammatory changes in vasculitic neuropathy [29] .
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Other Tests

Nerve conduction studies and needle EMG aid in defining the location and type of lesion.

  • Nerve conductions should show isolated peroneal nerve abnormalities. If the lesion is at the knee, then conduction block or, less commonly, conduction velocity slowing over that segment of the nerve should be documented. When axonal loss occurs in direct nerve trauma or with long-standing compression, a small compound muscle action potential may be noted. If other mononeuropathies with conduction blocks are found, then consideration should be made for an underlying vasculitis causing mononeuritis multiplex or possibly for hereditary neuropathy with liability to pressure palsy. If more diffuse nerve abnormalities are noted, then a generalized neuropathy should be considered, especially chronic inflammatory demyelinating polyneuropathy.
  • 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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Histologic Findings

Peroneal neuropathy from intraneural ganglia of the peroneal nerve may have various patterns: outer (epifascicular) epineurial, inner (interfascicular) epineurial, and combined outer and inner epineurial. [30]

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