Carpal tunnel syndrome (CTS) is caused by high pressure within the carpal tunnel which results in ischaemia of the median nerve. The resulting impaired nerve conduction causes paraesthesia and pain.
Untreated CTS can lead to permanent nerve damage.
Approximately 3-5 per cent of people have CTS. The incidence is highest in those aged between 45 and 64 years, and in this group women are three times more likely to be affected.
The cause of CTS is unknown in most cases. Occupational activities may contribute, particularly where the wrist is held in an exaggerated position for a prolonged period of time or where there is repetitive movement or vibration.
Certain risk factors exist, and can be thought of as secondary causes for CTS. The most common are rheumatoid arthritis and pregnancy. Certain individuals may be genetically predisposed to this condition.
1. Signs and symptoms
Characteristically a patient will complain of tingling, numbness or pain in the distribution of the median nerve. The patient may also complain of weakness in the hand and poor thumb grip. Pain and paraesthesia are often worse at night.
Some patients may exhibit atypical symptoms, with sensory disturbances in all fingers.
Physical examination in a patient with CTS may be normal. Wasting of the muscles in the thenar eminence and sensory loss may be found in the median nerve distribution. Opposition of the thumb may be impaired.
2. Screening tests
Phalen's test, which involves flexing the wrist for 60 seconds, leads to pain or paraesthesia in the median nerve distribution.
Tinel's sign is positive if tapping lightly over the median nerve at the wrist (volar aspect), leads to shooting pain and paraesthesia in its distribution.
The carpal tunnel compression test (Durkan test) involves applying pressure on the carpal tunnel to compress the underlying median nerve. The thumbs are applied to the proximal edge of the carpal ligament (the proximal wrist crease) and a positive test is one where the CTS symptoms are reproduced. These tests assist in the diagnosis of CTS but are not truly diagnostic.
3. Differential diagnosis
Numerous conditions are misdiagnosed as CTS. A patient with predominant pain symptoms (rather than paraesthesia) probably does not have CTS.
Cervical radiculopathy, ulnar neuropathy and other peripheral neuropathies may cause similar symptoms. The median nerve can be compressed at sites other than the carpal tunnel.
4. Confirmatory tests
Investigations are usually performed if diagnosis is uncertain, symptoms and signs are atypical, screening tests are equivocal or if first-line treatment has not worked.
Electrophysiological testing is commonly performed to establish or exclude CTS. Nerve conduction studies (electroneurography or ENG) are usually performed for diagnosis (sensitivity 85 per cent and specificity 95 per cent). Electromyography (EMG) is sometimes used but is less sensitive than ENG.
High resolution ultrasono-graphy is available in some areas as a diagnostic tool. It is increasing in popularity as it is quick, relatively cheap and non-invasive. MRI can be used when electrophysiological studies are equivocal and will precisely define the median nerve and anatomy in the carpal tunnel.
Patients with mild to moderate symptoms usually respond well to non-surgical treatments.
CTS in pregnancy improves after delivery in 68 per cent of patients. The condition may spontaneously resolve within six months in younger patients, especially if it is unilateral.
General measures to treat CTS include rest and reduction of activity. Patients should be advised to wear a wrist splint at night and to maintain the wrist in a neutral position.
Effectiveness of splints should be assessed at two months.
About 50 per cent of patients will benefit from splinting. There is no evidence for the use of NSAIDs or diuretics in CTS.
Analgesics and corticosteroid injections are used in the management of CTS, the latter where conservative measures have failed or where the symptoms are severe. Local cortico- steroid injections tend to provide short-term relief of symptoms but, beyond one month, significant effectiveness has not been demonstrated.
Surgical decompression of the carpal tunnel can be performed endoscopically or via an open approach. Endoscopic approaches tend to have shorter recovery times and fewer wound problems, thus facilitating an earlier return to daily activities. Conversely, endoscopic procedures are more likely to cause transient neurological problems such as neuropraxia, sensory impairment and paraesthesia.
In 80 per cent of cases, surgical decompression provides a complete cure.
Consider referring patients when the diagnosis is uncertain or where treatments have failed to work after three months. Refer patients with severe symptoms, especially if there is motor weakness of the thumb or persistent sensory or motor disturbance.