1.What is it?

Carpal tunnel syndrome is a set of signs and symptoms caused by compression of the nervus medianus (the median nerve in the arm) in the area of its passage through the carpal tunnel. This is a narrow channel formed by the small bones of the wrist and a sturdy envelope of connective tissue between the pads formed by the muscles that activate the little finger and the thumb and that are located at the root of the palm of the hand. The flexor (bending) tendons of the fingers and the nerve, which is the most delicate structure and therefore the most sensitive to pressure, run through this tunnel.

schematic drawing of the disposition of the carpal tunnel in the wrist

Illustration: On the left, a schematic drawing of the disposition of the carpal tunnel in the wrist; on the right, a cross-section of the wrist in the area of the carpal tunnel. The carpal tunnel consists of a kind of gutter (U-shaped in cross-section) formed by the wrist bones and closed off at the top by the ligamentum carpi, the transverse fibrous band holding together the bones of the root of the hand on the palm side. In carpal tunnel syndrome this channel is too narrow for its content, which consists of the flexor tendons (the tendons of the forearm which flex, or bend, the hand) and the median nerve, which becomes broadened and flattened through compression.

2.Symptoms

The symptoms are caused by the nerve becoming compressed, and consist of a tingling or painful sensation in the hand and the fingers, in particular in the area served by the median nerve, i.e. the thumb, index and middle fingers and part of the ring finger. Other symptoms include numbness of the finger tips and weakness that could result in dropping things. The pain can radiate via the forearm and the elbow into the shoulder.

The symptoms often become more severe during the night, even waking the patient. However, they can also manifest during the day, with activities as varied as driving, reading the newspaper or riding a bicycle. Symptoms may also become worse after hefty manual labour. Carpal tunnel syndrome can sometimes appear in both hands.

3. Cause

The pinching of the nerve in the narrow carpal tunnel is usually caused by a swelling of the sheathing of the tendons. Connective tissue may swell, among other reasons, due to hormonal causes. Thus the syndrome can occur in pregnancy and menopause, and is also seen, although less frequently, with hypothyroidism (a dysfunction in the operation of the thyroid gland, where it produces less hormone than would be normal) and excess production of growth hormone (acromegaly, or excessive growth of certain bones). In addition, the tendon sheath can swell through irritation, for example because of rheumatism, or after heavy manual labour. Carpal tunnel syndrome is a frequent occurrence in patients with diabetes mellitus. Sometimes there are other reasons why the carpal tunnel becomes too narrow, such as a bone anomaly (e.g. a fracture).

4. Examination

The type of symptoms will already give some indication of the appropriate diagnosis. The physical examination may detect sensitivity disorders in the thumb, index and middle fingers and the thumb muscles can seem a little thinner in places, but mostly no anomalies are found. A similar syndrome, which because of its resemblance can cause confusion as concerns the diagnosis, occurs with compression of the nerve by a cervical hernia, due to arthritis (wear and tear) of the cervical vertebrae, or with narrow spatial relationships in the shoulder area. The neurological examination must rule out these causes if appropriate, as they would naturally require a different type of treatment. A blood test may be made to determine causes; if a skeletal cause is suspected, an X-ray may be taken. A muscle examination called electromyography or EMG (a test that measures muscle response and which will show a delayed response of the electrical nerve activity in the area of the median nerve that is located within the carpal tunnel if present) can be used to confirm the diagnosis. This examination will primarily tell the neurosurgeon whether there really is a compression of the median nerve or whether the problem is caused by another compressed nerve, mostly in the neck.

5. Treatment

Once the diagnosis is certain to be carpal tunnel syndrome, the neurosurgeon will discuss the treatment options with the patient. Sometimes no treatment is necessary, or it is possible to wait if the symptoms are mild and of a temporary nature (for example, during pregnancy).Also, a small plastic splint may be appropriate to provide some rest to the wrist and enable symptoms to subside. An injection into the wrist with cortisone, a hormone produced by the cortex of the suprarenal glands (located just above the kidneys) and a local anaesthetic can be fairly effective for quite a while. Often the treatment of choice will be surgery, and in this case the splint can provide relief while bridging the waiting period.

6.Surgery

Anticoagulants (blood thinning medicine) must be stopped before the operation in consultation with the doctor. Usually, local anaesthesia will be used on the patient's hand and forearm. Once the anaesthesia has taken effect, the procedure will not cause pain. Sensitivity in the fingers often remains, but no pain is felt. The connection between the muscles for the thumb and the little finger, that is the roof of the carpal tunnel, is cut through, releasing its contents, in particular the soft nerve, from the compression inside the tunnel. Some surgeons prefer to carry out this procedure as an endoscopic operation (with a viewing device inside the wrist). The operation takes approximately a quarter of an hour. After bandaging the hand sometimes the arm is put in a sling.

7. After the operation

After a few hours the anaesthesia will wear off and any post-operative pain can be relieved with paracetamol, potentially combined with codeine (Dafalgan/Dafalgan codeine). It is advisable to keep the fingers moving normally, but the palm of the hand should be allowed to rest, and leverage-type movements such as wringing should be avoided for a few weeks. This type of rest is necessary for the wound to heal undisturbed, as otherwise it could open up again once the stitches are removed. Because the use of the hand that was operated on is seriously impaired during this two-week period, in patients who have carpal tunnel syndrome in both hands the procedure is usually only carried out on one hand at a time and not on both simultaneously. The wound must be kept dry. The bandage can be removed after one week and the stitches will be removed after ten days to two weeks.

8. Consequences of the operation

The tingling in the fingers usually disappears quickly, but can also take longer to fade away. This certainly applies to cases where there was some loss of sensation in the fingers before the operation ; this will sometimes remain. The scar in the palm can remain sensitive for a few months, and it can take even longer until the patient regains the full strength of his or her hand.

9. Complications

As is the case with any operation, a carpal tunnel syndrome operation can also lead to unexpected complications. However, such complications seldom occur. They consist primarily of post-operative bleeding and infection. Patients should contact their neurosurgeon in case of excessive pain or discharge from the wound.

Sometimes a small nerve branch running to a number of small muscles at the base of the thumb can become damaged because it branches off from the area in which the procedure on the median nerve takes place. This does not usually lead to noticeable symptoms, but sometimes movement in the thumb can be impaired. In rare cases the operation does not work and must be repeated.

A serious, but luckily very rare complication following an operation and which cannot really be foreseen is hand dystrophy (weakness and wasting). With this condition, the entire hand will swell up and be painful, especially with movement, and colour will vary from red under warm conditions to pale white or blue with cold.