27th June 2023

Mononeuropathies

Mononeuropathy refers to a lesion of a single nerve. The most common causes being compression or vascular. Common mononeuropathies include carpal tunnel syndrome and common peroneal palsy.

Common nerve palsies

Median nerve compression

Carpal Tunnel Syndrome is the most common upper extremity mononeuropathy. Compression of the median nerve at the carpal tunnel leads to symptoms of pain and paraesthesia of the lateral three and a half fingers. In severe cases it can also cause weakness in thumb abduction and wasting of the thenar eminence.

• Phalen’s sign: flex the wrist for about one minute, this will cause traction of the median nerve. A positive test will elicit pain and/or paraesthesia in the innervated fingers.
• Tinel’s sign: tap on top of the carpal tunnel, a positive test will elicit pain and /or paraesthesia of the innervated fingers.

The anterior interosseous nerve is the largest branch of the median nerve, originating distal to the lateral epicondyle. Palsy here can lead to inability of thumb and index finger opposition.

Common peroneal nerve palsy

The common peroneal nerve is motor to tibialis anterior and peronei muscles (peroneus longus, brevis and tertius). Neuropathy here, therefore, will result in foot drop (weakness of dorsiflexion) and weakness of foot eversion. Patients may also have sensory loss of the dorsum of the foot. Over time there will be wasting of the anterior tibial and peroneal muscles. The most common cause is the entrapment of the nerve at its origin, the fibular neck.

Other mononeuropathies