The carpal tunnel is a bony trough sealed with the flexor retinaculum, containing the median nerve and nine tendons.
The median nerve supplies sensation to the thumb, index and middle fingers, part of the ring finger, and the thenar eminence muscles. Any swelling in the tunnel easily compresses the median nerve.
The syndrome occurs more commonly in women and has a variety of causes.
These include fluid retention (often from pregnancy), synovial thickening secondary to rheumatoid arthritis or Colles' fractures, myxoedema, acromegaly, amyloidosis, diabetes and obesity. Local ganglions or lipomas can also contribute.
The condition can be induced by activities involving repetitive wrist flexion causing tendon sheath inflammation.
The first symptoms usually appear at night. The patient wakes a few hours after falling asleep with burning and numbness of the hand. Typically, the little finger is spared (supplied by the ulnar nerve), and also the lateral palm (the median nerve palmar cutaneous branch passes outside the tunnel).
Symptoms may worsen after repetitive wrist activity, and patients may also experience diminished manual dexterity such as difficulty buttoning clothes. In time, paraesthesia is replaced by pain, which can radiate up the arm. Eventually numbness occurs.
Early on there may be no signs, but in time thenar eminence wasting and reduced sensation may be found.
Two provocation tests aid diagnosis: Tinel's (tapping) test and Phalen's (flexing) test. Tinel's test aims to reproduce symptoms by percussing the median nerve at the wrist. Phalen's test is more reliable - holding the wrist hyperflexed for one or two minutes to elevate tunnel pressure reproduces the symptoms.
Because carpal tunnel syndrome is so common, alternative diagnoses are easily overlooked. These include peripheral neuropathy, mononeuritis, cervical spondylosis or thoracic inlet tumours involving the brachial plexus.
Care should be taken not to confuse this syndrome with symptoms of a herniated cervical disc. Examination should include the upper limb and neck. If there is doubt, consider nerve conduction studies in conjunction with clinical findings.
In mild cases, a wrist splint may help, particularly for nocturnal symptoms. This is appropriate for pregnancy-associated symptoms, which usually resolve on delivery.
Other conservative treatments include diuretics, NSAIDs and hydrocortisone injections. Care should be taken not to inject into the median nerve.
If the patient is still troubled after three injections, surgical decompression is recommended. Surgical decompression increases tunnel volume and is also indicated when signs and symptoms are persistent and progressive, especially if thenar atrophy is noted.
The operation divides the flexor retinaculum through a longitudinal incision.
Care is needed to avoid injuring the palmar sensory branch of the median nerve, which may develop a painful neuroma if it is accidentally severed.
The hand should be used as soon as possible after surgery, but the dependent position avoided.
After surgery, numbness may remain for a time, but recurrence is unusual.
Persistent unrelieved symptoms may result from incomplete flexor retinaculum resection or an error in diagnosis.
- Dr Lackey is a GP in Killingworth, Tyne and Wear, and Mr Sutton is a consultant orthopaedic surgeon in Northumberland
- Carpal tunnel syndrome should not be left untreated because it can eventually cause nerve damage.
- Tinel's test and Phalen's test help diagnosis.
- Failed conservative management or progressive symptoms, especially with thenar muscle atrophy, are indications for surgical treatment.
- Consider an error in diagnosis if there is a poor response to treatment.