Median Nerve Lesions and Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is by far the commonest cause of median nerve damage. It is caused by compression of the nerve between the transverse carpal ligament and the flexor tendons and carpal bones. Rarely, compression of more proximal parts of the nerve can occur at the forearm or elbow. The two significant conditions are pronator teres syndrome and anterior interosseous syndrome.

A recent study by the UK General Practice Research Database (253 practices) revealed 87.8 men and 192.8 women with new presentations per 100,000 population.¹ The commonest seen patients were in women aged 45-54. Other compression conditions, e.g. pronator syndrome, are much less common and tend to be seen in specific groups of workers.²

Carpal tunnel syndrome³

Vocational activities are often involved, but many other factors play a part. There is also a theory that patients who use their hands and wrists a lot are simply more aware of the symptoms.

Risk factors include:

• Genetic - square-shaped wrist, short stature, family history, hereditary neuropathy
• Secondary causes
  • Post-Colles fracture
  • Flexion/extension injury of wrist
  • Conditions encroaching on the space within the carpal tunnel (e.g. aneurysm, neurofibroma, haemangioma, lipoma, ganglion, xanthoma and gouty tophi)
  • Diabetes
  • Thyroid disorders (mainly myxoedema)
  • Menopause (including surgically-induced)
  • Inflammatory arthritides of the wrist
  • Acromegaly
  • Renal dialysis
  • Amyloidosis
• Vocational or leisure activities involving prolonged extreme posture of the wrist, high amounts of repetitive movement or exposure to vibration and/or cold are all associated with CTS
• Other factors - pregnancy, lactation, lack of aerobic exercise, use of walking aids

Other median nerve lesions

The main risk factor is occupational, e.g. dentists and shipyard workers using high-powered vibrating tools^4,5

Carpal tunnel syndrome³

Common symptoms include aching, burning, tingling or sensation of numbness in the first 3 digits, lateral aspect of the 4th digit and occasionally plantar aspect of the hand. Symptoms are typically worse at night, the offending hand being hung out of the bed at odd angles to try and revive it, and following strenuous wrist movement. Pain may become more persistent, and may radiate to the forearm, elbow, arm and shoulder.

Weakness may be noted in hand grip and opposition of the thumb. Phalen's sign – maintaining wrist at maximum flexion for 30-60 seconds or Tinel's sign - tapping the medium nerve at the level of the carpal creases, should reproduce paraesthesiae but are less reliable than clinical symptoms.

Other median nerve lesions

Nerve damaged at the elbow or forearm causes inability to flex the index finger and distal phalanx of the thumb with weak flexion of the middle finger and defective opposition of the thumb.⁶ This has been described as 'simian'. There may be significant sensory loss over palm and some fingers with skin becoming dry reddened and atrophic. With partial lesions, causalgia may develop hours or days later with dry scaly skin.⁷

Carpal tunnel syndrome⁸

Other conditions which should be considered include other median nerve compression syndromes, cervical radiculopathy, shoulder bursitis, thoracic outlet syndrome, TIA, myocardial ischaemia, tendonitis, fibrositis or lateral epicondylitis.

Other median nerve lesions

The list of differential diagnoses is similar to carpal tunnel. In addition, pronator syndrome and anterior interosseous syndrome need to be differentiated from CTS and from each other.

These are useful in patients whose clinical features yield a high index of suspicion for CTS but who fail to respond to first-line treatment.⁹

Carpal tunnel syndrome³

• Electroneurography (ENG) - nerve conduction studies have an 85% sensitivity and specificity greater than 95% for diagnosing CTS.The median nerve is stimulated proximal to the carpal ligament and compound muscle action potential is picked up over the thenar eminence.
• Electromyography (EMG) - this is useful in some cases but is not as sensitive as ENG.
• Ultrasonography - this is being increasingly used as a confirmatory test. Enthusiasts cite its wide availability, lower cost, non-invasiveness, and shorter examination time than electrophysiological studies. Ultrasound views of the median nerve show widening at the inlet of the carpal tunnel or flattening along the length of the tunnel was observed.¹⁰
• MRI - this can be used as an alternative to ultrasonography and when electrophysiological studies are ambiguous.

Other median nerve lesions

As with CTS, electrophysiology is the main investigation, but ultrasonography and MRI may be contributory where the findings are ambiguous.⁶

Carpal tunnel syndrome

Apart from the risk factors outlined above, CTS may also be associated with pyridoxine deficiency, obesity and chondromalacia.^11,12,13

Carpal tunnel syndrome³

Non-Surgical: A Cochrane meta-analysis did not support the use of non-steroidal anti-inflammatories, diuretics, or pyridoxine.¹⁴ A more recent systematic review found strong evidence for the use of local and oral steroids. There was moderate evidence that pyridoxine was ineffective but that splints were effective. The evidence for NSAIDs, diuretics, yoga, laser and ultrasound was limited or inconclusive. Exercise therapy and botulinum toxin B injection were found to be ineffective.¹⁵

Surgical: Carpal tunnel release may be performed by the open method or endoscopically. Trials suggest the effectiveness is similar in both methods, but there is a shorter recovery time after endoscopy.¹⁶ There is as yet insufficient evidence to state definitively whether surgical treatment is better than conservative therapy.¹⁷ Good results have recently been achieved using a specially-developed tool (the Knifelight) and minimally-invasive techniques.¹⁸

Other median nerve lesions

Rest and anti-inflammatories may be helpful. Decompressive surgery is sometimes required.⁶

Carpal tunnel syndrome

Definitive statements about prognosis are difficult because 'treatment failures' may sometimes be due to mis-diagnosis.¹⁹ Studies suggest that some patients do get better over time without treatment.²⁰ Severe symptoms seem to predict a more prolonged course.²⁰

Other median nerve lesions

Spontaneous improvement occurs rarely.¹⁷ There is a good response to surgical treatment, particularly where patients are selected on the basis of detailed investigation.²¹