eMedicine Specialties > Neurology > Electromyography and Nerve Conduction Studies

Median Neuropathy

Author: Charles Tuen, MD, Consulting Staff, Department of Internal Medicine, Section of Neurology, Methodist Medical Center
Contributor Information and Disclosures

Updated: Mar 27, 2007

Introduction

Background

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy in the upper extremity. The condition is usually bilateral, although the dominant hand tends to be more severely affected.

Pathophysiology

The median nerve crosses from the distal forearm to the hand through the carpal tunnel. The floor of the carpal tunnel is formed by the carpal bones and the roof by the transverse carpal ligament. Compression of the median nerve by the transverse carpal ligament (flexor retinaculum) can occur.

The palmar cutaneous branch of the median nerve leaves the main trunk 5-8 cm proximal to the wrist crease. It provides sensation to the thenar eminence and does not traverse the carpal tunnel. Loss of sensation over the thenar eminence is not part of CTS but suggests a lesion proximal to the wrist.

Frequency

United States

In Rochester, Minnesota, prevalence was estimated to be 125 per 100,000 during the period from 1976-1980. Most cases are idiopathic.

Other studies estimated the prevalence rates for CTS to be 1-5% in the general population and 5-15% in the industrial setting, but the rate is dependent on how CTS is defined.

Epidemiologic studies have demonstrated that the highest incidence of CTS tends to be in poultry processors and meat packing workers, followed by garment workers and automobile assembly workers.

Race

Findings of the 1988 National Health Interview survey indicate that CTS is 1.8 times more prevalent in whites than nonwhites.

Sex

Women are affected more than men. Phalen's series (1970) included 280 women and 96 men (female-to-male ratio 3:1).

Age

Of the patients in Phalen's series (1970), 58% were adults aged 40-60 years.

Clinical

History

CTS patients describe diffuse, poorly localized aching that can involve the entire hand and forearm.

• Many patients report that the entire hand falls asleep; if they are asked to note whether the little finger is involved, they subsequently note that the little finger is spared.
• Some patients also describe weakness, clumsiness, dry skin, coldness, swelling, and/or color changes in the hand. Nocturnal paresthesias may awaken the patient from sleep.
• Provocative factors: Symptoms are more common during a flexed or extended wrist posture. Discomfort may be provoked by driving or by holding the phone, a book, or a newspaper.
• Alleviating factors: Symptoms are relieved partially by changes in hand posture or shaking the hand.

Physical

Examination may be normal.

• Provocative tests: The Tinel sign, Phalen maneuver, and direct compression test are sometimes useful.
  • Tinel sign: Paresthesias are provoked by tapping over the median nerve at the wrist in 26-73% of patients with CTS and 6-45% of controls.
  • Phalen test: While holding the wrist flexed, paresthesia occurs within 1-2 minutes in 74% of patients with CTS and 25% of controls.
• Motor examination
  • Inspect the hand and check for muscle atrophy.
  • Test the strength of thumb abduction and opposition.
    • Isolating the muscle action of abductor pollicis brevis is difficult, since thumb abduction also may be performed by the abductor pollicis longus (ie, radial nerve).
    • A similar situation occurs with opponens pollicis since thumb opposition also may be produced by a combination of the flexor pollicis brevis (ie, deep head - ulnar nerve) and the flexor pollicis longus (ie, anterior interosseous nerve).
• Sensory examination
  • Two-point discrimination may be affected before pain and temperature sensation.
  • Even in severe cases of CTS, sensation over the thenar area usually is spared, as it is innervated by the palmar cutaneous sensory branch (a median nerve branch that arises proximal to but does not pass through the carpal tunnel).
• Dry skin may be seen on digits I-III.

Causes

• Most cases are idiopathic, but some cases may be caused by excessive and repetitive hand movements.
  • Highly repetitive wrist and finger use is a greater risk factor than forceful hand use.
  • The combination of finger flexion with repetitive wrist motion is probably the most provocative stressor.
  • The classic concept of repetitive motion-induced chronic tenosynovitis resulting in CTS has been questioned.
  • Keyboard data entry has not been established as a cause of CTS.
  • The relationship between carpal canal size and CTS risk remains controversial.
• The following list includes some underlying diseases and conditions associated with CTS:
  • Congenital - Persistent median artery, congenital small carpal tunnel, anomalous muscles (palmaris longus, flexor digitorum sublimis)
  • Connective tissue disease - Rheumatoid arthritis
  • Endocrine - Acromegaly, diabetes, hypothyroidism
  • Infectious/inflammatory - Histoplasmosis, Lyme disease, sarcoid, septic arthritis
  • Miscellaneous - Spasticity, especially with persistent wrist flexion, renal disease, hemodialysis, amyloidosis (familial and acquired), pregnancy, any other condition that increases edema or total body fluid
  • Trauma - Wrist fracture (particularly Colles fracture), hemorrhage (including anticoagulation)
  • Tumors - Ganglion, hemangioma, lipoma, neurofibroma, schwannoma
• Other diagnostic considerations
  • CTS versus C6 radiculopathy
    • The 2 conditions can coexist.
    • C6 radiculopathy usually causes neck and shoulder pain, weakness in C6 innervated muscles, and sensory loss restricted to the thumb.
    • Absence of nocturnal paresthesias and reproduction of the paresthesias with root compression maneuvers help to differentiate these 2 conditions.
  • CTS versus proximal median nerve problem
    • Flexor pollicis longus is innervated by the anterior interosseus nerve.
    • This muscle flexes the distal phalanx of the thumb and is not involved in CTS.
    • Even in severe CTS, sensation over the thenar area is spared, as it is innervated by the palmar cutaneous sensory branch (which arises proximal to and does not pass through the carpal tunnel).
  • CTS versus de Quervain tenosynovitis syndrome
    • Tenosynovitis develops in the abductor pollicis longus and extensor pollicis brevis tendons, which are held in a groove of the radius by a firm segment of the extensor retinaculum.
    • Signs and symptoms include the following: (1) pain in the radial aspect of the wrist and thumb that is aggravated by movement of the wrist and thumb; (2) pain and paresthesias radiating into the thumb, dorsum of the hand, and index finger due to irritation of the radial nerve by severe inflammation; and (3) pain when the thumb is flexed into the palm while the examiner deviates the wrist in the ulnar direction (ie, Finkelstein test).
  • CTS versus median neuropathy at the elbow and brachial plexopathy
    • Both median neuropathy and brachial plexopathy are rare.
    • The following findings may suggest a more proximal involvement of the median nerve: (1) sensory loss or paresthesia over the thenar eminence, in addition to the usual distribution of sensory disturbance in the fingers; (2) weakness of median innervated muscles proximal to the wrist, especially distal thumb flexion (flexor pollicis longus), arm pronation (pronator teres and pronator quadratus), and wrist flexion (flexor carpi radialis).
• Other risk factors for the development of CTS include ergonomic stressors, history of a median mononeuropathy, higher body mass index (BMI), history of diabetes, and rheumatoid arthritis.

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