Mononeuropathies

Key Features

Essentials of Diagnosis

• Focal motor or sensory deficit

• Deficit is in the territory of an individual peripheral nerve

General Considerations

• An individual nerve may be injured along its course

• An individual nerve may be compressed, angulated, or stretched by neighboring anatomic structures

• Nerve may be affected at a point where it passes through a narrow space (entrapment neuropathy)

Clinical Findings

Symptoms and Signs

• Entrapment neuropathies

  • May be asymptomatic

  • Symptoms may resolve rapidly and spontaneously

  • Symptoms may become progressively more disabling and distressing

  • Precise neurologic deficit depends on the nerve involved

• Involvement of a sensory or mixed nerve commonly results in pain distal to the lesion

• Percussion of the nerve at the site of the lesion may lead to paresthesias in its distal distribution

• Pronator teres syndrome affects the anterior interosseous nerve, a motor branch of the median nerve, that arises below the elbow between the two heads of the pronator teres muscle

  • A lesion may result after trauma or from compression, eg, from a fibrous band

  • Weakness is confined to the pronator quadratus, flexor pollicis longus, and the flexor digitorum profundus to the second and third digits

• Sciatic and common peroneal (fibular) nerve palsies

  • Most common etiology for sciatic nerve palsy is probably a misplaced deep intramuscular injection

  • Trauma to the buttock, hip, or thigh may also be responsible

  • The common peroneal (fibular) nerve itself may be compressed or injured in the region of the head and neck of the fibula, eg, by sitting with crossed legs or wearing high boots

  • Common peroneal involvement causes weakness of dorsiflexion and eversion of the foot, accompanied by numbness or blunted sensation of the anterolateral aspect of the calf and dorsum of the foot

• In tarsal tunnel syndrome, compression of the posterior tibial nerve or its branches between the bony floor and ligamentous roof of the tarsal tunnel leads to

  • Pain

  • Paresthesias

  • Numbness over the bottom of the foot, especially at night, with sparing of the heel

• In facial neuropathy, an isolated facial palsy is most often idiopathic (see Bell palsy) but may occur with

  • HIV seropositivity

  • Sarcoidosis

  • Lyme disease

Diagnosis

Diagnostic Procedures

• Electromyography and nerve conduction studies can be indispensable for the accurate localization of the focal lesion

• Entrapment neuropathy may be the sole manifestation of subclinical polyneuropathy, which can be excluded by nerve conduction studies

• Peripheral nerve tumors may be distinguishable from entrapment neuropathy only by

  • Noting the presence of a mass along the course of the nerve

  • Demonstrating the precise site of the lesion with appropriate electrophysiologic studies

Treatment

Medications

• Local infiltration of the region ...