Lower Extremity Neuropathies

, Ali T. Ghouse² and Raghav Govindarajan³

(1)

Parkinson’s Clinic of Eastern Toronto and Movement Disorders Centre, Toronto, ON, Canada

(2)

McMaster University Department of Medicine, Hamilton, ON, Canada

(3)

Department of Neurology, University of Missouri, Columbia, MO, USA

Sciatic Neuropathy

Sciatic neuropathies typically present with weakness and sensory loss in the sciatic nerve distribution over a lower extremity. It is not unusual for the peroneal distribution to be affected much more than the tibial division, because the peroneal division has few large fascicles with relatively little intervening fibrous tissue and the tibial division has many small fascicles cushioned by a large amount of fibrous tissue [2]. Sciatic neuropathy can result from hip surgery and may also result from injections in the gluteal muscles. Piriformis syndrome is another possible etiology of sciatic neuropathy, as in about 6 % of cadaver specimens the sciatic nerve passes within the piriformis muscle [1]. An important differential diagnosis is an injury to the L5, S1 roots, or a lumbar plexus lesion see Fig. 16.1.

Diagnostic Studies

1.

Motor nerve conduction studies of the peroneal and the tibial nerves are likely to show reduced compound muscle action potentials (CMAPs) compared with those obtained from the corresponding distal muscles. This helps in determining the degree of axonal loss but is not good in localizing the lesion. Similarly, late responses such as F-waves or the H-reflex can help to determine whether both the tibial and the peroneal branches are affected. Direct stimulation of the sciatic nerve at the gluteal fold is not a reliable technique for localizing sciatic neuropathy.
2.

Sensory nerve action potentials (SNAPs) of the sural and superficial peroneal nerves are useful to distinguish a postganglionic lesion (example: sciatic nerve or lumbosacral plexus) from a preganglionic lesion (example: root or cauda equina).
3.

Needle electromyography is useful for evaluating denervation or reinnervation after complete or very severe lesions. Muscles distal to the lesion such as the hamstrings, where the hamstring muscles could be examined, as well as the muscles innervated by the posterior tibial nerve and the common peroneal nerve. In a sciatic lesion, the gluteal muscles are generally spared and so also are the paravertebral muscles.

Case Study

A 58-year-old man sustained an injury to his right hip during a motor vehicle accident, with radiographs revealing an acetabular fracture treated with open reduction internal fixation (ORIF). Following the surgery, the patient woke up with a right foot drop.

Only gold members can continue reading. Log In or Register to continue