Median nerve neuropathy

Last updated: June 14, 2023

Summary

The median nerve is a peripheral nerve originating in the cervical roots C₅–T₁ of the brachial plexus. It supplies motor innervation to the anterior forearm flexors, the thenar muscles, and the two lateral lumbricals as well as sensory innervation to the lateral palm and anterior, lateral three and a half fingers. Motor and sensory deficits depend on whether the lesion is proximal (above the elbow) or distal (below the elbow). While proximal lesions present with the “hand of benediction,” distal lesions present with either the “pinch sign” (anterior interosseous nerve syndrome) or, in the case of carpal tunnel syndrome, with mildly impaired thumb and index finger motion. Both proximal lesions and carpal tunnel syndrome result in reduced sensation in the area of the thumb, index and middle finger. Anterior interosseus nerve syndrome does not cause any sensory deficits. Chronic injuries to the nerve result in atrophy of median nerve innervated muscles while acute injuries do not have this feature. Treatment is mostly conservative and focuses on rest and immobilization.

Etiology

Traumatic: e.g., fractures (humerus fracture causing proximal lesion), carpal bone dislocations, or penetrating injuries (gunshots, lacerations )
Chronic compression: : e.g., in the carpal tunnel (see carpal tunnel syndrome; ) or between the forearm muscles (anterior interosseous nerve syndrome) or by a nerve sheath tumor (schwannoma of the median nerve)

Neuroma (schwannoma) of the median nerve

References:^[1]

Clinical features

Course of the median nerve

Runs from the axilla to the elbow, in the medial side of the arm in the medial bicipital groove
Enters the forearm through the two heads of the pronator teres muscle
After branching off into a motor nerve (anterior interosseous nerve), courses distally between the superficial and deep layers of the forearm's flexor compartment
At the wrist, branches off into a sensory nerve (the palmar cutaneous branch of the median nerve)
Enters the hand through the carpal tunnel
For more information, see peripheral nerve injuries.

Median nerve

Lesions of the median nerve

Clinical features of median nerve lesions
Location of lesion	Motor deficit	Sensory deficit
Proximal (above anterior interosseous nerve origin)	Hand of benediction: when asked to make a fist, the patient can only flex the ring finger and the little finger due to Loss of thumb opposition and abduction Loss of index and middle finger flexion Impaired wrist pronation and flexion Thenar muscle atrophy (chronic injury)	Thumb Index and middle finger Radial side of ring finger
Distal (affecting anterior interosseous nerve)	Anterior interosseous nerve syndrome: loss of flexion in distal joints of the thumb and index finger, leading to an inability to pinch small objects (pinch sign) or form the “OK sign”	None
Distal (below anterior interosseous nerve origin)	Recurrent branch of median nerve Innervates muscles of the thenar eminence Damaged with lacerations of the radial-sided wrist and proximal palm Results in loss of thumb flexion, opposition, and abduction without sensory or other motor deficits Median claw: Distal median nerve injury causes palsy of the lumbricals I and II with preserved function of extrinsic flexors. This imbalance leads to permanent flexion of the index finger and the middle finger (aggravated when trying to extend the fingers). Ape hand: inability to oppose and abduct the thumb due to injury of the proximal or distal median nerves impairing the thenar muscles' functions Palmar cutaneous nerve Purely sensory nerve arising from median nerve proximal to the carpal tunnel Provides sensation to the palm	Thumb Index and middle finger Radial side of ring finger
Distal (within wrist)	Carpal tunnel syndrome Mild impairment of flexion of index finger, long finger, and thumb (less severe than in other median nerve lesions) Thenar muscle atrophy (in chronic injury)	Thumb Index and middle finger Radial side of ring finger

The hand of benediction only occurs in proximal median nerve injuries.

Proximal and distal median nerve lesions Pinch sign (anterior interosseous syndrome) Carpal tunnel syndrome Thenar muscle atrophy Sensory innervation areas of the peripheral nerves (arm, ventral view) Laceration of the hand

References:^[1]^[2]

Diagnosis

Physical examination
- Bottle sign
- In the case of carpal tunnel syndrome, the following signs are also present:
  - Tinel's sign
  - Phalen's sign
Diagnostic procedures
- Nerve conduction study
- Electromyography (EMG)

References:^[3]

Treatment

Avoid repetitive wrist activities
See treatment for carpal tunnel syndrome

References:^[2]

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